Ostracoda

Chapter 19

Ostracoda Alison J. Smith

L. Denis Delorme

Department of Geology, Kent State University, Kent, Ohio

621 Auburn Crescent, Burlington, Ontario, Canada

I.  INTRODUCTION

Contents I.  INTRODUCTION 725 II.  MORPHOLOGY AND PHYSIOLOGY A.  External Shell Morphology 726 B.  Internal Shell Morphology 727 C.  Body and Appendage Morphology D.  Internal Anatomy and Physiology E.  Life History 730

726

727 729

2.  Amphimixis and Parthenogenesis 731 3.  The Egg

732

4.  Hatching and Seasonality 732 5.  Molting

733

III.  ECOLOGY AND BEHAVIOR

734

1.  Benthic Swimmers 734 2.  Benthic Nonswimmers

734

3.  Lakes, Ponds, and Stream Habitats 734 4.  Aquifer Habitats 735

Ecology and Classification of North American Freshwater Invertebrates Copyright © 2010, 2010 Elsevier Inc. All rights reserved.

Ostracodes are common microscopic crustaceans found in almost all aquatic habitats and some terrestrial habitats as well. They provide valuable information concerning many aspects of environmental conditions, biological activities, and ecological processes. As more and more links are forged between environmental, genomic, and ecological subdisciplines, the value of Ostracoda as biological and geochemical indicators will continue to increase. The class Ostracoda within the subphylum Crustacea contains both marine and nonmarine forms; however, the focus of this chapter is upon the order Podocopida, which contains the extant nonmarine ostracode taxa (including strictly freshwater species) within the superfamilies Cypridoidea, Darwinuloidea, and Cytheroidea. Ostracodes are perhaps best known in field collections for the bivalved shell (carapace), thinly or heavily calcified by low-magnesium calcite, which is molted and replaced on average eight times as the animal grows to adulthood. Their valves are distinct from those of the conchostracan order Spinicaudata (see Chapter 20, this volume) in being much smaller (average length about 0.5 mm) and having no growth lines (Fig. 19.1). Ostracodes are free-living except for the Entocytheridae[120,237], which are commensal upon other crustaceans. Free-living ostracodes can be easily observed at the sediment-water interface or among subaquatic vegetation, and can be collected and reared in cultures without much difficulty. Indeed, the naturalist G.O. Sars studied ostracodes from many localities around the world by rearing cultures derived from dried pond mud that was sent to him[222]. This chapter will concentrate on nonmarine ostracode genera found in North America, with a special focus on some commonly distributed species likely to be encountered in routine aquatic sampling. At last count, there were 56 genera and about 420 species identified for this continent[70,172]. Ongoing studies of North American fauna in groundwater indicate that these numbers are increasing with increased sampling efforts, especially in

725

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Ecology and Classification of North American Freshwater Invertebrates

Figure 19.1  Size, color, and ornamentation vary considerably within the nonmarine ostracode superfamilies. Here is a selection of species from California springs, wetlands, streams, and lakes showing ranges in carapace length (0.5 to 2 mm), pigmentation (greens, blues, browns, and white, sometimes mottled or striped), and ornamentation (smooth to reticulated, occasionally with small spines). Specimens courtesy of Mark Angelos, Natural History Museum of Los Angeles County.

hypogean environments[2,236]. For additional and comprehensive information beyond the coverage presented in this chapter concerning the biology and ecology of extant nonmarine ostracodes, the reader is encouraged to seek out Maddocks[158], Martens[165], Meisch[186], and Holmes and Chivas[122], and the taxonomic bibliography of Kempf[134].

II.  MORPHOLOGY AND PHYSIOLOGY In general, adult ostracodes collected in North America range in size from about 0.4 mm to a little over 1 mm, with most less than 1 mm, although one genus, Cypriconcha, reaching lengths of 3–4 mm (Fig. 19.1). This small size necessitates microscopic analysis, and detailed shell or appendage analysis entails the use of a scanning electron microscope (SEM) or environmental SEM (ESEM). However, identification to the species level of many commonly distributed taxa can be achieved with a good binocular microscope with magnification power to about 200, using basic features of the ostracode carapace and appendages, and this chapter is written with this goal in mind.

A.  External Shell Morphology The ostracode body, or visceral mass, is completely encased within a chitinous and a low-magnesium calcite bivalved shell (carapace). The only exception is the entocytherid group of ostracodes which lacks calcium in the exoskeleton. Although molted, discarded, and replaced seven or eight times as growth proceeds, the calcite shell

is actually only part of a continuous chitinous cuticle[158] (Fig. 19.2). The exterior surface of the cuticle (exoskeleton) is made up of chitin[110]. The outer chitinous coating of the epidermis is the only covering over the calcitic shell. The soft epidermal tissue lining the interior part of the carapace is composed of the inner and outer epidermis. The epidermal cells of the outer lamella are larger and more irregular in shape than the inner epidermal cells. Subdermal cells occur between the inner and outer epidermal cells, as do the liver, ovaries, and testes. The epidermis is contained within a thin chitinous lining. When the ostracode molts, the complete exoskeleton is shed, leaving only the visceral mass and the soft tissue or epidermis. The epidermis is continuous with the visceral mass in the dorsal region of the body. Once the ostracode molts, the space between the epidermal cells of the outer and inner layer is empty. The shells are then secreted by the cells of the outer lamellae[261]. According to Turpen and Angell[261], calcium dissolved in water is the source of calcium for the shell. The necessary bicarbonate comes from the surrounding water. They used dissolved 45Ca as a tracer (pH 7.4, 23°C) to show that calcium is not resorbed from the shells prior to molting and that ostracodes do not store calcium in their bodies. In this characteristic, ostracodes are unlike many other crustaceans, such as decapods for example, which store a small percentage of calcium from the previous shell that is then reused in the new shell[199]. Chivas et al.[37] ran laboratory experiments on the Australian Mytilocypris henricae and found that temperature influenced the rate of shell calcification. Roca and Wansard[212] also found the rate of development to be linked to temperature. Using Herpetocypris brevicaudata, they showed that below 15°C the Ca content of valves is strongly diminished and the length of time for calcification was longer (17 days). The optimum temperature was 23°C with the fastest rate of calcification (3–7 days). Bodergat[20] demonstrated with microprobes that phosphorus was an integral part of freshwater ostracode shells. She further noted a significant positive correlation between the amount of shell phosphorus and the habitat temperature of the ostracode. The calcareous shell is the most obvious structure when the organism is viewed under a microscope. The shell is divided into two parts, the outer lamella and the duplicature (Fig. 19.2). The outer lamella is the major part of the shell, whereas the duplicature is the calcified part of the inner lamella bordering the posterior, ventral, and anterior margin. It forms a part of the free margin and projects toward the center of the carapace. The outer lamella may contain pores through which project setae, which are sensitive to touch. The duplicature is welded to the outer lamella around the margins, by a strip of chitin, which joins with the chitin coating and the chitin lining. This juncture is referred to as the line of concrescence or the distal line of adhesive strip (Fig. 19.2). Within the

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(outer lamella) (inner lamella) subdermal cell pigment body epidermal cell of inner layer chitin lining of epidermis supporting fibers inner margin CaCO3

nerve cell

middle cell accessory cell septa selvage groove list

epidermal cell of outer layer scolopoide body teminal filament chitin coating of epidermis distal cell normal pore canal

bulbous base of seta

flange

selvage duplicature

chitin coating of calcareous layer radial pore canal

and ­ environmental reasons. Genetic drift in localized ­populations may play a role in morphologic ­ variability, as will the supply of calcium in the water, which will influence the extent of calcification. For example, Limnocythere itasca has short recurved alae on its lateral surfaces. The individuals identified from Canada[62] and northern Minnesota[92] appear to be characteristic of this species. R. M. Forester (personal communication) identified L. itasca from the Laguna de Texcoco, Mexico, which have very long and delicate recurved spines or alae. Intermediate forms have yet to be recovered. In another example, the caudal process of the posteroventral portion of the right valve of the female Fabaeformiscandona caudata may be blunt[66] or sharp (C. novacaudata[15]). Both forms and intermediate morphs are found in Lake Erie. As a final example, Fabaeformiscandona rawsoni has a pronounced caudal process on the left valve of the female, and this shows considerable variability in size, leading to some taxonomic confusion. The many intermediate forms in the case of this species suggest ecophenotypic variation[245].

distal line of adhesive strip

Figure 19.2  Diagrammatic cross section of the shell and the enclosing dermal layers, vestibule located between the outer lamella and the shell portion of the inner lamella in the anterior portion of the shell. (Figure redrawn by J.L. Delorme from Kesling[135,136].)

chitinous strip, radial or marginal pore canals are found. These are very fine tubes through which setae pass. The inner free margin of the duplicature is referred to as the inner margin (Fig. 19.2). When the duplicature extends beyond the line of concrescence toward the center of the shell, a shelf is formed. The space between the shelf and the outer lamella is referred to as the vestibule (Fig. 19.2). Several structures are found on the duplicature which are very important in taxonomy down to the species level[249]. Pustules, teeth, or crenulations (Fig. 19.17d) may appear on the outer margin of the duplicature. A combination of septa, lists, and grooves are found on the duplicature. Some of these are shown in Fig. 19.2[135,136]. The shell may contain additional structures on the outer lamella such as lateral depressions called sulci. Raised areas variously termed alae, knobs, bosses, papillae, or pustules, depending on their shape, size, and orientation, may also be found on the shell surface. The surface of the shell may also be pitted, punctate, wrinkled, or have a reticulate surface. These ancillary structures of the shell are very often used for generic and specific identification[250]. Some authors, notably Benson[13,14], have discussed the roles of ornamentation, form, function, and architecture of the ostracode shell. Intraspecific morphological diversity of the shell may be pronounced. The reader should expect to see some variability in ornamentation on the valves for genetic

B.  Internal Shell Morphology Structures on the internal surface of the shell may also be used in ostracode systematics. Many ostracode muscles are attached directly to the calcareous shells because the chitinous exoskeleton does not provide sufficient rigidity to anchor many of the muscles. The points of attachment of these muscles leave scars as raised or depressed areas on the interior of the shell. For example, the closing or adductor muscles form a distinctive pattern of scars (Fig. 19.3) as do the mandibular muscles[12,15,239]. Traces of the ovaries and testes can also be seen in the posterior of the shell. Collectively, these scars commonly provide a good diagnostic tool with which the aquatic biologist can determine the superfamily and gender.

C.  Body and Appendage Morphology Ostracodes have their body (visceral mass and appendages) suspended from the dorsal region in an elongate, chitinous pouch. The ostracode has a shortened body with a slight constriction in the midregion that separates the head from the thorax[135]. There is no abdomen. Instead, the posterior of the body tapers off bluntly and ends in a pair of preanal furcae. The head region contains four pairs of appendages which are used for swimming, walking, and feeding. The thoracic region features two pairs (three pairs of some authors) of appendages used or adapted for feeding, creeping, and cleaning of the shells[27]. There is some debate as to whether the maxilla are cephalic or thoracic appendage[185]. Ancillary cuticular structures such as setae, claws, and pseudochaetae, found on most limbs, are ­ recognized

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Ecology and Classification of North American Freshwater Invertebrates

0.1

0

0.1

0.2 mm.

closing muscle scar

Zenker’s organ third thoracic leg

seminal vesicle

mandibular palp eye first antennae

penis

furca

maxilla

second antennae

branchial plate

A

prehensile palp of first thoracic leg

second thoracic leg

closing muscle scar mandibular palp first antennae

Figure 19.3  Central muscle scar (adductor) patterns (arrows point toward anterior of carapace): (A) Cytheroidea—note the vertical stack of 4–5 scars; (B) Darwinuloidea—note the circular rosette of approximately 10–12 segments; (C) Cypridoidea—note elongate scars, openly arranged appearance; (D) Cypridoidea—family Candonidae—note the more tightly arranged “pawprint.”

as important in functional morphology and systematics[27]. Appendages are shown in Figs. 19.4–19.7. The head region is composed of the forehead, the upper lip, and the hypostome. The four pairs of appendages in the head region are the first antennae (antennules), second antennae (antennae), mandibles, and maxillae. When the distal four podomeres of the first antennae have very long, plumose setae, the ostracode is a good swimmer (e.g., Cypridopsis vidua). The first antennae are curved up and backward. If these setae are absent, as in the darwinulids (Fig. 19.5) and the limnocytherids (Fig. 19.6), the ostracode cannot swim. The second antennae extend down and curve backward. These appendages are robustly constructed and have a strong claw for walking and climbing. Swimming setae may be present on the first podomere of the endopodite. These structures are used for rowing when the ostracode is swimming. Ostracodes that swim maintain a sustained motion. The swimming setae of the first antennae used in propelling the animal forward must be in constant motion or the animal will sink to the substratum. Observation of the swimming motion, using a binocular microscope, shows the swimming setae moving in a pattern similar to a handheld eggbeater directed upward. Because swimming is energetically quite expensive, ostracodes can only swim short distances (usually between adjacent plants).

0.1

0.2 mm.

eye

maxilla

B

third thoracic leg uterus 0.1 0

second antennae

branchial plate first thoracic leg

furca second thoracic leg

Figure 19.4  Sketch of the internal morphology of (A) male and (B) female Candona suburbana Hoff (Cyprididae) from Kesling[135]. First thoracic leg is referred to as the maxilla or maxillar endopodite and the second and third thoracic legs as the first and second thoracic legs in the text. (Figure redrawn by J.L. Delorme.) mandibular palp closing muscle scar eye first antennae

second antennae 0.1

0

egg

maxilla first thoracic leg branchial plate second thoracic leg 0.1

third thoracic leg

0.2 mm.

Figure 19.5  Sketch of the internal morphology of a female Darwinula stevensoni (Brady and Robertson) (Darwinulidae) from Kesling[135]. First thoracic leg is referred to as the maxilla or maxillar endopodite and the second and third thoracic legs as the first and second thoracic legs in the text. (Figure redrawn by J.L. Delorme.)

In most species, well-developed mandibles occur between the upper lip and the hypostome. The dorsal tips of the mandibular palps are attached to the interior of the shell by muscles. The ventral portion of the palps ­terminate

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mandibular palp first antennae

eye

0.1

closing muscle scar

0

branchial plate

0.1

0.2 mm.

penis

maxilla second antennae

first thoracic leg second thoracic leg

third thoracic leg

Figure 19.6  Sketch of the internal morphology of a male Limnocythere sanctipatricii (Brady and Robertson) (Cytheridae) from Kesling[135]. First thoracic leg is referred to as the maxilla or maxillar endopodite and the second and third thoracic legs as the first and second thoracic legs in the text. (Figure redrawn by J.L. Delorme.) mandibular palp eye first antennae

penis branchial plate

maxilla

second antennae

first thoracic leg third thoracic leg second thoracic leg

Figure 19.7  Generalized sketch of the internal morphology of a male entocytherid (Cytheridae) from Hart and Hart[111]. First thoracic leg is referred to as the maxilla or maxillar endopodite and the second and third thoracic legs as the first and second thoracic legs in the text. (Figure redrawn by J.L. Delorme.)

in heavily toothed mandibles: these teeth grind the food before it is ingested. A respiratory (branchial) plate extends from the mandibular palp. On the ventral portion of the head is located a keel-shaped structure called the hypostome, which forms the mouth. Rake-shaped organs are situated at the rear of the mouth. They consist of chitin shafts with terminal toothed structures and are used for straining and feeding. The fourth and final set of cephalic appendages is the maxillae. The maxillae, located on either side of the hypostome posterior of the mandibles, are made up of several cylindrical masticatory processes (maxillula). The maxillae pass the small particles toward the mouth. What were previously referred to as the first thoracic legs of most cyprids are now referred to as part of the maxillae. In other groups, this part of the maxillae (formerly the

first thoracic legs) are modified in male ostracodes into ­prehensile palps (Fig. 19.4a) used in grasping the female shell during copulation. There are two pairs of thoracic appendages. The first thoracic legs (previously called the second thoracic legs) are robustly developed and used for walking, climbing, and clinging onto surfaces. The second thoracic legs (formerly called the third thoracic legs), or cleaning legs, are the most flexible and well-muscled appendages. The end of these legs, in most ostracodes, are modified pinchers used to grasp and remove foreign objects from between the shells. In the entocytherid group, the modified maxillae and the two pairs of thoracic legs (Fig. 19.7) are modified terminally as hooks to hold onto the gills of the host crayfish[111]. Morphological diversity can be seen in the first thoracic legs. These can be modified for feeding, for use during copulation (prehensile palps), or for walking. The commensal entocytherids have modified the maxillae and two thoracic legs for grasping onto the gills of the host. Paired hemipenes are found in syngamic species behind the third thoracic legs on the ventral side of the thorax. Paired uterine openings lie behind and inside the vaginal openings of sexual and asexual females. The distal part of the thorax terminates in paired furcae. In some species, these are whip-shaped structures, while in others they are well developed and armed at the end with long, serrated claws. Rome[215] and Triebel[258] considered the furcal attachment to be an important biocharacter to be used in systematics. Meisch[187] argued that the furca evolved from uropodal plates and are best termed uropodal rami in the Podocopida. Sexual dimorphism is common in ostracodes, and can often be quite pronounced in external shell features, as in the limnocytherids and candonids. Gender in most cases can be determined visually with a microscope. This is done by observing the presence/absence of testes and traces of the testes on the inner surface of the shell, Zenker’s organs (see Section II.D), modification of the male maxillae (formerly called the first thoracic leg) into prehensile palps, hemipenes, and ovaries. For many species, it is necessary to separate the valves to view these organs. Generally, the male is larger than the female, although this is not always the case. In candonids, only the male has an anteroventral notch on the shell.

D.  Internal Anatomy and Physiology The circulatory system of freshwater ostracodes lacks both heart and gills. Gaseous exchange is through the entire surface of the body and particularly through the membranous inner lamella of the exoskeleton. The respiratory plates of some appendages move and renew oxygenated water past the inner surfaces of the organisms. Large respiratory cells are known to occur in the inner lamella, forming a ­respiratory epithelium over the valve cavity which forms a blood sinus[18].

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The digestive system of ostracodes consists of the mouth, esophagus, stomach, intestine, rear gut, and anus. The mouth is a large opening with the large teeth of the mandibular palps on either side. A gland, probably a salivary gland, opens into the mouth. The esophagus is very muscular and leads into the distended stomach. The hepatopancreas (liver) is found in the epidermal layers next to the shells and empties into the anterior part of the stomach. Most of the digestion takes place in the stomach where the food is formed into balls, which pass from the stomach through the rear gut for absorption of the nutrients and exit the anus as fecal pellets. Approximately eight excretory glands, including the liver, have been identified in freshwater ostracodes. McGregor[176] showed that for Chlamydotheca arcuata some food particles pass through the hepatopancreas, aiding in the digestion of food. Most glands have been studied in considerable detail[17,29,82,139,214,224]. The nervous system of the ostracode is composed of a cerebrum (protocerebrum, deutocerebrum, and tritocerebrum[108,260,271]), circumesophageal ganglion, and a ventral chain of fused ganglia[135]. The first and second antennae, mandibular palps, and maxillae have small ganglia which connect to the central nervous system. The ostracode has a single median eye made up of three optic cups each containing lenses. The number of cells composing a lens is variable[196,214]. The black opaque eye lies in the anterior part of the body just below the rim of the shells. When the shells are open, the animal can detect shapes and motion; however, when the shells are closed it can only distinguish light intensity. Subterranean-interstitial (hypogean) ostracodes are blind[45]. The ovaries are found in the epidermis next to the shell as a continuous sequence of gametes. The ova are fairly large in the last instar of many species, forcing the chitin coating of the epidermis into the space normally occupied by the shell. When the new shell is secreted, a trace of the ovaries is commonly seen as part of the shell’s inner structure, as in the Candoninae. The testes are similarly placed and appear as traces on the inner and posterior region of the shell, as in the Candoninae. For some genera (e.g., Bradleystrandesia) the testes form a spiral around the inner edge of the shell rather than being confined to the posterior area. The testes of Cyprididae change into the vasa deferentia as they leave the epidermis and enter the body cavity. The vas deferens joins up with the ejaculation ducts or Zenker’s organs (Fig. 19.4a). These large organs are made up of longitudinal muscles in the shape of a tube on which are found radiating bristles and are covered in a chitinous sheath. The alternate contraction and expansion of these paired organs forces the sperm into the hemipenes during copulation. Zenker’s organs lie in a nearly ­horizontal position in the posterior part of the body cavity and are visible in many live specimens. The hemipenes are very complex structurally. The ostracode must rotate them

before copulation can take place[43,138,139,178,179]. Zenker’s organs are absent in the Cytheridae and Darwinulidae: in the Cytheridae, the testes and ovaries are found next to the intestine. For further details on the anatomy and physiology, refer to Maddocks[157,158].

E.  Life History 1.  Reproduction Broadly speaking, ostracodes develop from eggs, pass through eight molt stages (ecdysis), and reach sexual or asexual adulthood in the final molt within a few months to over 1 year (life spans of up to 4 years have been recorded for Darwinula stevensoni[209] ). Ecdysis ends in the adult stage. However, there is considerable variability in the details of how reproduction, egg development, and life cycle processes proceed. Nonmarine ostracodes reproduce both sexually (amphimixis) and asexually (apomictic parthenogenesis). Four reproductive modes have been identified in nonmarine taxa: fully sexual reproduction, mixed reproduction, fully parthenogenetic reproduction among populations with sexually reproducing congeneric relatives, and ancient parthenogens[186]. Sexual reproduction is common. A tally of extant North American ostracode species indicates that of those examined, 80 species are asexual and 111 are sexual[10,115]. A full discussion of ostracode reproductive modes can be found in Meisch[186] and in Martens[165]. Ostracodes have paired reproductive organs in both sexes, and in many taxa, especially among the Candonidae and the Limnocytheridae, there are gender-specific carapace shell shape and size characteristics. This sexual dimorphism in the carapace often leads to males and females being identified mistakenly as two different species, but this problem can be averted by close examination of appendages and certain shell features. In particular, the observer should note the presence/absence of testes and traces of the testes on the inner surface of the shell, Zenker’s organs, hemipenes, ovaries, and modification of the male maxillae into prehensile palps. For many species, it is necessary to separate the valves to view these organs, although the trace of the testes and the presence of the Zenker’s organ are typically observable through the shell wall. In candonids, an added clue can be found in that only the male has an anteroventral notch on the shell. Certain physiological accommodations occur in the arrangement of the reproductive organs in ostracodes that make the group somewhat unusual. The reproductive organs in males and females take up a lot of space within the carapace: up to one-third of the volume of the entire animal[49]. In females of the Cytheroidea and Darwinuloidea, the gonads are located inside the body, whereas in the Cypridoidean females, the gonads are located in the space between the inner and outer ­lamellae

Chapter  |  19  Ostracoda

of the shell. For the observer, traces of the gonads can be seen marking the inside of the Cypridoidean shell when viewed in transmitted light. In males of the Cytheroidea (and the recently observed rare males of the Darwinuloidea), the gonads are also housed inside the animal (near the intestine) and there is no Zenker’s organ, but instead there is an internal sperm pump[186,238]. In Cypridoidean males, the gonads are located partly between the valve lamellae but also extend along the inside of the shell, and these traces as well as a Zenker’s organ can be clearly observed in transmitted light. The sperm of ostracodes is among the largest produced in the animal kingdom[156] (exceeded only by certain species of Drosophila[200]), and in many cases the spermatozoa exceed the length of the ostracode carapace. For example, Meisch[186] reported that for Cyclocypris ovum (carapace length of 0.5–0.7 mm), the sperm length is 6 mm, approximately 10 times the length of the animal! For males, the production and presentation of such large sperm results in extensive coiling of the testes, and in the occurrence of paired ejaculation ducts or Zenker’s organs, as is the case for Cypridoidea, or internal sperm pumps, as in the Cytheroidea. Both hemipenes function during copulation, and multiple sperm are delivered, as has been observed in dissection of Eucypris virens[262]. Although some questions occur in the early literature as to whether ostracode sperm are functional[156], genotypic frequencies in populations with males examined electrophoretically are in close agreement with those expected in a randomly ­mating sexual population[115]. Chaplin[31] demonstrated successful karyogamy in Candonocypris novaezelandiae, and Matzke-Karasz[173] demonstrated that fertilization occurs in Pseudocandona marchica and that paternal mitochondrial derivates are present in the egg after fertilization. The female ostracode has paired vaginal openings, oviducts, and ovaries housed in the genital lobes. For sexually reproducing females, the spermatozoa are received into the seminal receptacles housed in the genital lobes. In transmitted light, the sperm are often visible within the seminal receptacle and are identifiable by a spiraled, coiled line[173]. Some podocopid lineages exhibit brood care, with females having distinct brood chambers, as seen in Cytheridella ilosvayi. Brood care is common in the Darwinuloidea and Cytheroidea but absent in the Cypridoidea. In the cases of brood care, eggs are retained within the posterior portion of the female carapace until hatching and often through the first two or three instars. Far more typical, however, are those that do not brood, and instead place and glue eggs onto a suitably firm surface, such as shells or sand grains, and then abandon them[124].

2.  Amphimixis and Parthenogenesis Chaplin et al.[33] reviewed the sex mechanisms for freshwater ostracodes. Although males are the heterogamic sex,

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some species have XO or XY sex determination systems. They determined that a case of multi-X systems is found in Heterocypris incongruens where the females have six pairs of X chromosomes and the males have six X and a Y chromosome. Further, they report that males of this species produce two types of sperms, one with five and the other with 10 chromosomes. Lécher et al.[152] found that some parthenogenetic ostracodes have supernumerary chromosomes, and that they have complex sex chromosome mechanisms with XO, XY, and multiple Xs and Ys. Three Canadian sexual ostracodes (Cypricercus splendida, C. deltoidea, and C. tincta) possess 22 chromosomes[259] each. For C. deltoidea and C. tincta, meiotic pairing was seen. These authors further indicate that the asexuals, Cypricercus horridus, C. reticulatus, and C. fuscatus, had variable chromosome counts and no evidence of meiotic pairing was observed. Electrophoretic studies by Havel et al.[116] showed that 10 of 12 asexual ostracodes included clones which were polyploid. They also found that clonal diversity varied among species. For instance, Heterocypris incongruens averaged 1.2 clones (1.3 clones Havel and Hebert[117]), whereas Cypridopsis vidua had 8.3 clones (9 clones Havel and Hebert[117] ) and Cypricercus reticulatus averaged 7.8 clones[117] per pond. On a regional basis, high-­diversity species indicate a range of 18–80 clones while low­diversity species show 1–7 clones[117]. Bell[10] indicated that parthenogenesis is more common in disturbed habitats, whereas syngamy is more common in stable habitats, such as permanent or ancient lakes. Further, it has been proposed that these geographic and habitat distributions of parthenogens versus sexual populations may be linked to both ecological and geological habitat stability, with parthenogens being more successful in establishing populations in stable environments in the short term[125]. The study of ostracodes from various habitats from the Canadian Arctic to the southern United States[117] to tropical habitats in Jamaica[49] does not yet show an influence of latitude on the prevalence of asexual versus sexual reproduction. However, Horne and Martens[125] found distinct geographic patterns to European distributions of asexual versus sexual populations, and hypothesized that climatic stability, including postglacial conditions following the end of the Pleistocene, may have had an impact on population range expansion. Schön[225] tested this hypothesis by applying nested clade analysis to DNA sequences of two European species of asexual nonmarine ostracodes, and concluded that asexual populations did not show evidence of faster postglacial range expansion, but could not rule out the possibility that more recent dispersal events may mask the record. Hybridization has been documented between the asexual Heterocypris incongruens and Cyprinotus glaucus[34,259]. Diploid asexual species when fertilized by a sexual species produce an asexual triploid. Suspected

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Ecology and Classification of North American Freshwater Invertebrates

hybridization between Cypricercus reticulatus and other sexual cypricercids in Canada has been postulated[259]. Theoretical models predict that sexually reproducing species should have selective advantage in unstable environments; however, a study by Chaplin and Ayre[32] did not indicate a complete association of sexually derived recruitment in unstable environments. The Ostracoda include a lineage of ancient asexuals which are the subject of considerable and often controversial research. Darwinulids have apparently maintained parthenogenesis for as long as 70 million years[170], and the cosmopolitan Darwinula stevensoni has done so for approximately 25 million years[171]. Recently, three males were identified in a darwinulid population of the genus Vestanelula[238] but none had identifiable sperm, and thus may not be reproductively functioning males. The significance of the find of the male darwinulids is threefold: (1) the occasional occurrence of sexually nonfunctioning males in an otherwise parthenogenetic population may be atavistic; (2) dissection of the males demonstrated the absence of a Zenker’s organ, a taxonomically important observation; and (3) the dissection of the males made it possible to dismiss a nineteenth century report of a male darwinulid, which has now been shown to be incorrectly identified[171]. There is considerable research underway into the genetics of parthenogenesis, especially regarding darwinulids, and an in-depth review of this research can be found in Martens[165] and Schön et al[226].

3.  The Egg The freshwater ostracode egg is a double-walled sphere of chitin impregnated with calcium carbonate. The space between the two spheres is occupied by a fluid[274]. These two characteristics of the egg allow it to withstand desiccation and freezing. Most ostracode eggs are white, but some are green (Cypridopsis vidua) or bright orange (Heterocypris incongruens, Potamocypris smaragdina). Eggs are slightly flexible, with a thin (2 m) chitinous coating, and in the case of the common Pseudocandona marchica, have an average diameter of about 90 m[173]. All North American freshwater ostracodes are oviparous, except several species of Darwinula and the marine brackish water Cyprideis, which are ovoviviparous. These taxa brood their eggs in the posterior of the carapace from which the nauplii are released. Brood pouches are more common in marine ostracodes.

4.  Hatching and Seasonality Most species begin hatching in the spring in the temperate zone. The timing of this process is controlled in part by temperature and geography (latitude). Species which live in temporary (vernal) ponds have a shorter life cycle. For example, Cypridopsis vidua develops in about 1 month[135],

while Cypria turneri requires several months[247]. Some of these same species can also exist in permanent ponds where several generations per year may develop. For some species (e.g., Fabaeformiscandona caudata[66,67] and Cyprinotus carolinensis[174]), hatching is delayed and spread over a much longer period. These apparent resting eggs allow the animal to sustain itself in the habitat in spite of stressful periods (such as anoxia and pollution[66]) when the nauplii cannot survive. Eggs produced by some species can be either spring or summer forms. The ostracodes hatched from eggs laid in the spring do not tolerate warm summer temperatures. Ostracodes hatched from eggs laid in the summer will live only in warm water and expire in cold water[224]. Martens et al.[167] noted that the eggs of the Australian Mytilocypris henricae would not hatch below a certain temperature. The eggs of freshwater ostracodes can withstand freezing[135,241]. As early as 1915, Alm[1] noted that temperatures affected the time of hatching. Ephemeral ponds, in which the sediments stay frozen for up to 6 months during the winter, produce many nauplii from eggs in the spring. Angell and Hancock[4] found that the eggs of “Heterocypris incongruens” could withstand freezing and remain viable down to –18°C when either wet or dry. Some authors have hatched ostracode eggs from dry lacustrine sediments kept in their laboratories for periods ranging from a few years to many decades[222,228]. McLay[183] reported that the eggs of Cypricercus reticulatus do not hatch until dried. Angell and Hancock[4] found that the eggs of “Heterocypris incongruens” remained viable after drying at 22°C and 40°C. The eggs did not remain viable if kept wet and heated to 40°C. The eggs of some species (Cypridopsis vidua, Cyprinotus incongruens, Physocypria sp., and Potamocypris sp.) can pass through the lower intestinal tract of both wild and domestic ducks and remain viable[203]. Kornicker and Sohn[144] reported that ostracode eggs were still viable after being egested by goldfish and swordtail fish. In an excellent paper detailing a meticulously carried out experiment, Rossi et al.[216] and Angell and Hancock[4] have shown that an individual of Heterocypris incongruens during its lifetime can produce both diapausing eggs and eggs that hatch within a few days. Rossi et al.[218,220] showed that the ratio of resting eggs depends on the genotype, temperature, and photoperiod. They also indicated that the percentage of dormant eggs increases with temperature and daylight hours in a winter clone and decreases in the summer clone. Their studies showed that egg hatching decreases at higher temperature, was unaffected by photoperiod in the winter clone, but increased with both temperature and daylight hours in the summer clone. Rossi et al.[216] found a rather high number of first hatchlings (neonates) at the end of the experiment for the winter clone when they removed the algal mat to count the cluster of eggs. They suggested that

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Chapter  |  19  Ostracoda

bioturbation may play a role in the hatching of eggs under field conditions. Rossi and Menozzi[217] found from laboratory experiments that the dominant clone from the field had a better chance of survival at low temperatures and conversely the dominant summer clone survived better at high temperature. This indicates that temperature is most likely responsible for seasonal cycles. Most ostracodes are controlled seasonally in their habitat. Research on seasonality has concentrated on those species living in temporary ponds. For temporary ponds in the temperate zone, early spring collections made after the basin receives water yield few live ostracodes[84,121]. In these ponds, a regular succession of juveniles can be observed until the pond dries up, with some species exhibiting at least two generations per year. A temporary coastal habitat investigated by McLay[182184] has ostracodes from the fall through to the late spring. Ostracodes were absent through the summer because of desiccation of the habitat. Freezing had only a marginal effect on a part of the habitat. McLay[183] stated that the maturation rate was 190 days for Herpetocypris reptans and 45 days for Cyprinotus carolinensis. In permanent ponds, active species are absent for several months[83]. Juveniles began appearing in early spring and continued until late spring, while adults were present until late fall to early winter. This pattern was repeated for the three species studied by Ferguson: Cypridopsis vidua, Potamocypris smaragdina, and Physocypria pustulosa. Ostracodes that live in ponds or ephemeral bodies of water have a short life cycle. Martens et al.[167] noted that an Australian species took longer (4–5 months) to reach

sexual maturity in the winter than in the summer (2–3.5 months). Candona subtriangulata, Cytherissa lacustris, and Darwinula stevensoni, which inhabit large lakes, where the habitat is considered to be stable, will have a life cycle of 6–24 months[66,177,209]. The length of the life cycle depends on the species. Danielopol[46] observed the length of the life cycle for five species. These ranged from 126 to 489 days, the latter being for a hypogean ostracode.

5.  Molting During the eight molt stages, the appendages change in size, shape, and function, and these differences are very useful in determining which instar has been collected, or whether adults are present as well as juveniles. A summary of these developments is found in Table 19.1 (after Kesling[135]). Przibram[204] determined that crustaceans doubled their weight from one molt to the next. He further concluded that because weight varies directly with volume, that volume would also increase by a factor of two. This led him to believe that a given linear dimension would increase by about the cube root of two (1.26) for each molt. Based on this hypothesis, Kesling[137] devised a circular slide rule which allows one to determine the variability of any linear dimension, area, or volume of any ostracode molt stage and adult. This slide rule is useful in determining which molt stage (shell or appendage) one is examining. Being able to identify an ostracode as an instar saves time because most instars cannot be identified to the species level.

Table 19.1  The development of appendages with each instar of the nonmarine ostracodes. Note that a () indicates the anlagen of a structure Instar

1

2

3

4

5

6

7

8

9 (Adult)

Antenna I



















Antenna II



















Mandible



















Maxilla

















Furca

























































Leg I Leg II Leg III Ovaries Testes

734

Ecology and Classification of North American Freshwater Invertebrates

For some common forms, examination of the duplicature (calcified inner lamellae) can quickly distinguish an instar from an adult, as in the example shown in Fig. 19.8, in which the adult shows a wide anterior and posterior duplicature compared to the instar.

III.  ECOLOGY AND BEHAVIOR A.  Distribution Ostracodes are found in nearly every conceivable aquatic habitat and typically occupy multiple habitats. These range from temporary and permanent ponds, lakes, intermittent and permanent streams, to ditches and irrigation canals, hot springs and seeps of all kinds, and fens. Caves and the interstices of oxygenated aquifers are additional habitats. Some—referred to as semiterrestrial ostracodes—are found in moist organic mats and hydrated soils of fens and in axial cups of bromeliads. North American nonmarine ostracodes thrive in a full range of salinities from 5.5 mg/L (Hemlock Lake, Wisconsin, with Candona elliptica and Cyclocypris ampla) to 109,658 mg/L (Lake Abert, Oregon, with Limnocythere sappaensis)[93]. Coastal areas that receive salt spray and inland waters with a source of sodium chloride often have estuarine taxa such as Cytheridella, Cyprideis, and Cytheromorpha[11,194]. De Deckker[50] lists an Australian species found in saline

waters of greater than 170,000 mg/L, and it is interesting to note for comparison that the upper limit for nonmarine ostracodes in North America is around 100 g/L[93].

1.  Benthic Swimmers Ostracodes are benthic organisms and are only rarely found in the plankton. They are divided into swimmers and nonswimmers, based on the presence or absence of long plumose setae on the antennae. Most often, they swim between aquatic plants in the littoral or photic zone. If they are disturbed while swimming, they often lose control and spiral down to the substrate. A few species of the genera Cypria and Physocypria are known to sometimes swim up into the water column, as they have been occasionally recovered from suspended sediment traps. Another swimmer, Notodromas monacha, turns upside down when approaching the water surface, and with its flat venter, adheres to the underside of the water surface by surface tension. Marmonier et al.[161] indicated that plant-dwelling species such as Cypretta brevisaepta, Cyclocypris ovum, and Cypridopsis vidua are more likely to be spherical in shape.

2.  Benthic Nonswimmers The nonswimmers, or true benthic forms, use their welldeveloped antennae (without setae) and first thoracic legs to crawl on the sediment–water interface or burrow in and out of the upper 2 cm of sediment. Some species, such as the limnocytherids, are also infaunal, crawling beneath the sediment–water interface between the sediment particles (L. Delorme, personal observations and Benzie[16]). Ostracodes live in the vents of warm and cold-water springs where groundwater is discharging[88,180,232], and can tolerate hot springs with temperatures in the range of 40–55°C[146,272].

3.  Lakes, Ponds, and Stream Habitats

Figure 19.8  Distinguishing between adult and juvenile (instar) forms: the Candonidae show distinct differences in the duplicature (calcified inner lamellae) when comparing an adult (female Candona ohioensis, above) to a juvenile (Candona ohioensis below). Note the widening of the duplicature in the anterior and posterior portions of the shell (blue arrows) in the adult compared with the juvenile. White arrows point toward the anterior of shell.

Most freshwater ostracode species may be found in more than one habitat. The pond–lake habitats can be viewed as a continuum from shallow to deep water. Some ponds are temporary in nature and, therefore, harbor a specific faunal association such as Candona renoensis, Cypricercus (now Bradleystrandesia) deltoidea, Megalocypris (now Cypriconcha) alba, and Cyclocypris laevis[68,140,273]. At the opposite end of the scale are those species adapted or restricted to living in permanent lake habitats (Candona subtriangulata, Cytherissa lacustris, and Cytheromorpha fuscata). A faunal mix may occur between pond–lake and stream habitats. There may be a specific biotope developed at the mouth of a stream or river where it enters the lake or pond. The delta area is characterized by a combination of flowing and standing water. Many ostracode species are

735

Chapter  |  19  Ostracoda

adapted but not restricted to living in this biotope, such as Candona acuta, Cyclocypris ampla, C. sharpei, Ilyocypris bradyi, I. gibba, and Potamocypris variegata. Large lakes have bottom currents which accommodate such species as Fabeformiscandona caudata and C. acuta. None of the species listed by Delorme[68] are completely restricted to flowing water. Those which are considered as lotic (fluvial) species are Candona acuta, Cypria obesa, Ilyocypris bradyi, I. gibba, and Potamocypris variegata. In an analysis of the distribution of the 89 species represented in Version I of the North American Nonmarine Ostracode Database NANODe[93], 51 species are present in springs, 59 species in wetlands, and only 15 species in streams[232]. Species distributions among these 157 sites show strong differences in hydrologic habitat. For example, whereas some species such as Cypridopsis vidua and Ilyocypris gibba are common in all three habitats, other species such as the spring species Cavernocypris wardi, Candona sigmoides, and Psychrodromus canadensis are particular to one type of habitat. Species collected in streams but not found in wetlands or springs include Candona acuta, Candona albicans, Limnocythere friabilis, Limnocythere reticulata, and Potamocypris smaragdina. Species collected in wetlands but not found in springs or streams include Candona decora, Candona distincta, Candona inopinata, Candona paraohioensis, Candona patzcuaro, Candona renoensis, Cyclocypris serena, Cypria obesa, Cyprideis beaconensis, Cypris subglobosa, Cyprois marginata, Herpetocypris reptans, Heterocypris punctata, Limnocythere bradburyi, Limnocythere herricki, Limnocythere itasca, Limnocythere inopinata, Limnocythere ornata, Limnocythere paraornata, Scottia browniana, and Strandesia retensis. Finally, species collected in springs and not found in streams or wetlands include Candona candida, Candona compressa, Candona crogmaniana, Candona sigmoides, Candocyprinotus ovatus, Cavernocypris wardi, Chlamydotheca arcuata, Cyclocypris ampla, Cyclocypris ovum, and Psychrodromus canadensis. Most of these species also co-occur in lakes in the NANODe database as well, which strongly suggests that many so-called lacustrine species may in fact be living in nearby streams, springs, and wetlands and are washed into the lakes or living in the groundwater discharge points along the lake margins[232].

4.  Aquifer Habitats Hypogean (subterranean) ostracodes are being recovered more frequently from aquifers. These ostracodes are small (0.5 mm), typically blind, and live in oxygenated aquifers with fracture flow (such as karstic aquifers) and also matrix flow (such as sand aquifers), where the base of the food chain is chemolithotrophic bacteria. They are recovered by pumping the aquifer or trenching through it[45], or in aquifer discharge areas (springs and seeps), particularly after

substantial rainstorms. In North America, karstic aquifers such as the Edwards Aquifer (Texas) and the Nevadan Lower Carbonate Aquifer have produced endemic ostracode fauna that are largely undescribed[89,154,206]. Many of these taxa exhibit seemingly exotic carapace morphologies, with spines and shapes similar to the morphologies seen in other relatively isolated and stable aquatic systems in the world, such as Lake Tanganyika. Besides their obvious value to biodiversity and potential as biogeochemical indicators, research suggests that changes in abundances in deep aquifer discharge sites reflect recharge history and activity of the aquifers[65,89,205]. Forester[89] (page 1) hypothesized that these hypogean ostracodes “occupy shallow ground-water islands within the regional groundwater flow systems.” Discharge points for these two aquifers are springs (Nevada) and combinations of springs and streams (Texas), and these are sites where hypogean taxa can be collected. Marmonier et al.[161] showed that interstitial ostracodes often have a geometric shape (triangular or trapezoidal) which is most suited to its habitat. The same can be said for most limnocytherids which live just below the sediment–water interface, crawling between the sediment interstices (Delorme, personal observations). Ward et al.[267] observed the highest concentration of hypogean ostracodes in a well close to the main channel of the Flathead River, Montana, and in wells farthest on the floodplain but near the Whitefish River. There is no doubt that much work and discovery remains to be done in examining the hypogean ostracodes in the numerous extensive aquifers in North America.

5.  Shallow Interstitial and Hyporheic Habitats Numerous species live in the hyporheic zone of streams and in shallow, interstitial habitats. They are often overlooked but represent a significant part of the aquatic habitat. In many cases, by including these taxa in diversity studies of streams and wetlands, the number of species is substantially increased. To date, the most detailed studies on the ostracodes of hyporheic environments in North America that demonstrate this increase in species richness are studies on the Flathead River, Montana[242], the South Platte River, Colorado[268], and the Pomme de Terre River, Minnesota[235]. Rogulj et al.[213] indicated that those hypogean ostracodes (such as Fabaeformiscandona wegelini) that live in shallow interstitial habitats are closely linked to running water rich in organic matter. This hypothesis is supported by observations of Rouch and Danielopol[219] and Marmonier and Creuzé des Châtelliers[48]. Cavernocypris wardi has been recovered from spring and interstitial water of the Flathead River, Montana[267], from the South Platte River, Colorado[163,164], and from springs in Wyoming, Nevada, and Colorado[88]. Cavernocypris subterranea has been reported from a spring near Brush Creek,

736

Ecology and Classification of North American Freshwater Invertebrates

Idaho (common in Europe)[147]. Undescribed species of Nannocandona and Schellencandona have been recovered from springs supported by deep aquifers in West Virginia[236]. Not all ostracodes found near spring discharges are hypogean, as many surface water species find a suitable habitat in these sites as well[88,180,267].

6.  Bromeliad Habitats Axial cups are formed by the spiral overlap of bromeliad leaves. These cups collect rainwater and become inhabited by many kinds of invertebrates. Tressler[256] described Metacypris maracoensis, recovered from the axial cups of Florida bromeliads. Ostracodes of the genus Metacypris, Elpidium, and Candonopsis are found associated with bromeliads in Central and South America and on Caribbean islands[44,153]. A key to their dispersal mechanisms was recently found by Lopez et al.[155] who noted that Elpidium passed through the gut of bromeliad tadpoles alive, and were also able to attach themselves to the skin of frogs and salamanders, an action that could allow them to move to new bromeliads.

7.  Cave and Sinkhole Habitats Ostracodes have been recovered from several caves. Klie[142] reported Entocythere donnaldsonensis commensal on the crayfish Cambarus from the Donnelson Cave of Indiana. From the Marengo Cave of Indiana, Klie named two new species: Candona marengoensis and C. jeanneli (now Pseudocandona[185]). Hart and Hobbs[112] have described eight new troglobitic cave species from the eastern United States. Walton and Hobbs[266] also described troglobitic ostracodes from Florida caves. Pools in deep sinkholes in limestone terrain (cenotes) of Yucatan, Mexico, have a rich and varied ostracode fauna. Furtos[98] described 23 species from these habitats.

B.  Physicochemical Characteristics Nonmarine ostracodes have been found to respond to hydrochemical ecotones created by rock–water interactions or solute evolution[30,86,207,230,231]. De Deckker and Forester[54] hypothesized that ostracode species diversity would be highest near or in a range centered on the calcite branch point (the first mineral branch point reached in natural waters, discussed below), whereas with increasing salinity, species abundance would continue to climb while species richness would be expected to fall. This hypothesis was validated by Smith[230,231] who demonstrated this relationship in lakes of the northern Midwest of the United States. Species abundance continues to increase with increasing ionic concentration in the saline lakes of the northern Midwest of the United States. In North America, the upper tolerance limit for ostracodes in nonmarine

saline water appears to be approximately 100 g/L, although in Australia, this limit is not reached until approximately 300 g/L[54]. Delorme has found that a high percentage of genera (61%) in the Delorme Database (samples from approximately 6700 stations in Canada collected between 1965 and 1976 and now housed in the Canadian Museum of Nature) are found only in bicarbonate-dominated waters. Bicarbonate, after being converted to carbonate, is a primary constituent of the shell. Only 9% of the genera in the Delorme database are found living in sulfate-rich or dominant waters. Several genera (30%) have species which have a preference for either of the two types of water. Chloridedependant species, such as Cytheromorpha fuscata and species of Cyprideis, are more properly tolerant of marine brackish water. C. fuscata are occasionally found in inland lakes[194] where brine seepages occur. Such species as Candona rectangulata, Cyprinotus salinus, and Cypris bispinosa are found in lake and pond habitats that may receive sea spray. These species are by no means restricted to chloride-enhanced waters.

1.  Salinity and Solute Composition Salinity (the total concentration of major ions expressed in milligrams per liter) and solute composition (the major ion composition of water, expressed typically in milliequivalents per liter or milligrams per liter) are important to ostracode physiology, ecology, and biogeography. In North America, natural water salinities range from extremely dilute (5 mg/L recorded in NANODe) to hypersaline (400 g/L)[119,151]. Nonmarine ostracodes occur in the lower range, from 5 mg/L to about 100 g/L, although most species are limited to less than 30 g/L. Physiologically, osmotic regulation is affected by salinity and so is the balance between calcification and ion regulation[189]. Radke et al.[208] have shown the sensitivity of ostracodes to the alkalinity/Cl activity ratio in water of increasing salinity. The major ion composition of natural waters in North America ranges from dilute, calcium-magnesium­bicarbonate water to higher concentrations that are variously dominated by chloride, sulphate, or bicarbonate anions, and calcium, magnesium, or sodium cations. The ionic composition (solute composition) as well as the concentration (salinity) play a major role in the biogeography of ostracodes in North America because they are important ecological as well as mineralogical parameters in hydrologic processes. The relationship of species distribution to ionic composition and ionic concentration in nonmarine environments can only be summarized here, drawing from a recent discussion of this relationship by Smith and Horne[235]. In dilute water below approximately 300 mg/L, bicarbonate, calcium, and magnesium are the most common major ions. With increasing salinity (e.g., in evaporative conditions, or solute input from groundwater),

737

Chapter  |  19  Ostracoda

these ionic concentrations rise, until calcite saturation is reached and calcite precipitates, at a total ionic concentration of approximately 300 mg/L. This is the calcite branch point, the first mineral branch point occurring in natural waters[81]. Beyond that point, the water becomes depleted in calcium and enriched in bicarbonate, or vice versa, resulting in a solute path toward bicarbonate-enriched, calcium-depleted saline water or bicarbonate-depleted, calcium-enriched saline water (Fig. 19.9a). Ultimately, other mineral branch points (such as gypsum, for instance) will be reached, and further changes in major ion composition will occur. Hydrochemically, the fate of a water body in an evaporative setting is determined at the calcite branch point[81], although changes in the solute path can occur if hydrochemically different water is added. The major ion composition of water that has evolved beyond the calcite branch point, rather than salinity, becomes critical in determining which species will be present. For example, Forester[86] noted that different species of Limnocythere could be found in lakes with the same salinity but of different ionic composition. There are boundaries, which Forester identified as hydrochemical ecotones, which define the habitats for these species (Fig. 19.9b). This observation was confirmed and further developed by many workers[41,87,90,93,207,230,231,254]. Although the Limnocythere genus remains the most clearcut example of this hydrochemical partitioning, many

A

other ­ostracode ­species respond to these solute differences. Thus, ­ knowledge of which species respond to different solute paths is very useful in reconstructing hydrochemical changes within lakes.

2.  Dissolved Oxygen Dissolved oxygen in the aquatic habitat is an important requirement for survival. The mean requisite for dissolved oxygen by ostracodes falls within a very narrow margin of 7.3–9.5 mg/L[70]. In general, the concentration of dissolved oxygen in the water is broad. Candona subtriangulata has the highest minimum oxygen requirement of 5.6 mg/L. A high number of species (34 out of 43, in Canadian habitats; L. D. Delorme, unpublished data) can tolerate low dissolved oxygen concentrations (Fig. 19.10). Those species which require a minimum 3 mg/L dissolved oxygen in the water are Cytherissa lacustris, Cytheromorpha fuscata, Ilyocypris gibba, Limnocythere ceriotuberosa, L. herricki, L. itasca, L. verrucosa, and Potamocypris variegata. Delorme[66] found that Fabaeformiscandona caudata could survive in Lake Erie even though the hypolimnion has summer dissolved oxygen content below its lower tolerance limit of 2.8 mg/L. Its survival was accomplished by having a short life cycle allowing it to produce eggs before the onset of anoxia. This survival mechanism has been in place for some time in Lake Erie as indicated

B

100000

All NANODe sites

10000

Alkalinity/calcium (meq/L)

10000

Alkalinity/calcium (meq/L)

100000

1000 100 10 1

1000 100 10

1 0.1

0.1

0.01

0.01 1

10

100

1000

10000

100000 1000000

Total dissolved solids (TDS) (mg/L)

All NANODe sites Sites with C. ohioensis Sites with L. ceriotuberosa Sites with L. staplini

1

10

100

1000

10000

100000 1000000

Total dissolved solids (TDS) (mg/L) Sites with C. elliptica Sites with L. itasca Sites with L. sappaensis

Figure 19.9  Major ion hydrochemistry of approximately 600 surface water sites in NANODe[93] showing: (A) solute distribution of alkalinity/calcium in meq/L versus increasing concentration as total dissolved solids in mg/L and (B) distribution of selected ostracode species showing preferences for ranges of ionic compositon as well as concentration.

738

Ecology and Classification of North American Freshwater Invertebrates

Dissolved oxygen mg/L Physocypria pustulosa Cyclocypris laevis Candona ohioensis Cyclocypris serena Candona renoensis Darwinula stevensoni Cypria ophtalmica Pseudocandona compressa Cypria obesa Pseudocandona albicans Bradleystrandesia reticulata Candona candida Fabaeformiscandona protzi Limnocythere verrucosa Cypridopsis vidua Cyclocypris ovum Cyclocypris sharpei Candona paraohioensis Cyclocypris ampla Physocypria globula Candona decora Ilyocypris gibba Potamocypris smaragdina Cypriconcha alba Candona acutula Candona distincta cytheromorpha fuscata Ilyocypris bradyi Limnocythere staplini Cypris pubera Potamocypris unicaudata Candona acuta Limnocythere varia Potamocypris variegata Fabaeformiscandona rawsoni Cypricercus deltoidea Heterocypris glaucus Potamocypris granulosa Limnocythere itasca Limnocythere ceriotuberosa Fabaeformiscandona caudata Cytherissa lacustris Candona subtriangulata

0

5

10

15

20

25

Figure 19.10  Dissolved oxygen range for some Canadian freshwater ostracodes. The solid line represents the mean, the bars represent the minium and maxium values (modified from Delorme[70]).

by the ­ presence of fossil shells in the lake sediments[67]. Contrary to F. caudata, C. subtriangulata and Cytherissa lacustris have become locally extinct in the central basin of Lake Erie because they have a 1-year life cycle and cannot reach sexual maturity as they require a minimum dissolved oxygen content of 5.6 and 3.0 mg/L respectively. Cytherissa lacustris is making a comeback with a reduction in anoxia. Newrkla[195] found that C. lacustris could survive at 1 mg O2/L in the laboratory on a glass substratum and minimal food (20°C and 20 hr exposure). Nine of the 43 species examined in a previous study[70] can tolerate near-zero dissolved oxygen (below the detection limit of the Winkler Azide Method, APHA 1965) for short periods. Candona decora, Cyclocypris ampla, C. sharpei, and

Cypria ­ophtalmica have been recovered from water of zero dissolved oxygen from a small river in early December (L. D. Delorme, unpublished data). The river had been covered by about ⅓ m of ice, suggesting that these waters had been anoxic for some time. Fox and Taylor[94,95] have found by experimentation that some ostracodes survive longer at oxygen levels below air saturation of 21%.

3.  Temperature The water temperature of the aquatic habitat plays an important role in the habitat, seasonal, and geographical distribution of ostracodes. This is not to say that other factors such as availability of food, solute composition, turbidity, and energy levels are not important. The temperatures in shallow water habitats can range from 0 to over 30°C, depending on the latitude and altitude. Species living in this niche must have the ability to tolerate this broad range in one or more life stages. Such species as Candona acutula, C. candida, C. ohioensis, Cyclocypris ampla, C. sharpei, Cypria ophthalmica, and Limnocythere staplini exhibit such a range for bottom water temperature. The exceptions to the above are shallow groundwater-fed streams, which may have a nearly constant temperature. Candona subtriangulata has a low mean value of 5.5°C, with a range of 2.6–19.2°C[66]. This species is common in Lakes Superior, Huron, and Ontario at considerable depth, where the bottom water temperature does not vary much. Korschelt[145] ran several experiments with Cypridopsis vidua and Cypria ophtalmica, in which the species were frozen in ice for several hours. The ice was then allowed to melt; the majority of the specimens survived the freezing experiment. At the other temperature extreme, Cypris balnearia has been described from thermal springs at temperatures of 45–50.5°C. Wickstrom and Castenholz[272] recovered Potamocypris from an algal–bacterial substratum of a hot spring, in Oregon, at temperatures ranging between 30 and 54°C. Chlamydotheca arcuata has been found in warm springs (Utah, Nevada, Arizona, and Mexico) where the water temperature varies between 24 and 39°C[88] and Thermopsis thermophila has been recorded from a hotspring of 40–50°C in Nevada[146]. Mean annual air temperature assists in explaining the geographic distribution of ostracodes in habitats shallower than 25 m. In a study of Canadian freshwater ostracodes, Delorme[70] determined that 20 out of 43 species can live in aquatic habitats north of latitude 60°. The minimum values of the range for mean annual air temperature for these species habitats are between –8.5 and –11°C. The species restricted to the arctic and low mean annual air temperatures are Candona paralapponica, C. protzi (may belong to Fabaeformiscandona, see Meisch[185], not confirmed for North America), C. anceps, C. pedata, C. mülleri,

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C. ikpikpukensis, Cyclocypris globosa, Limnocythere liporeticulata, and Tonnacypris glacialis. The habitats for those species living in the midlatitudes have a mean annual air temperature greater than 1.5°C.

4.  Sediment–water Interface, Particle Size,   and Food The distribution of ostracodes at the sediment–water interface is a function of the availability of food, whether the substratum surface is clearly or poorly defined, the particle size distribution of the top centimeters of the substratum, as well as the time of year. The distribution of ostracodes is patchy. Where there is organic detritus, ostracodes will be abundant, particularly in shallow water. The presence of abundant floating organic debris just above an illdefined sediment–water interface discourages ostracodes from living in this part of the habitat. As detritivores and herbivores, ostracodes require a ready source of particulate organic matter that they can sweep into the mouth region. They also use their mandibular teeth to rasp or gnaw off small particles from large organic particles, living plants, or algae. On predominantly mineral substrata, ostracode densities will be low. As the sediment–water interface becomes deeper and further from the shoreline, the number of species decreases. In this niche, the only food available will be the resistant cellulose raining down through the water column, bacteria, and fungi. In the deep troughs located in the eastern end of Lake Superior, only Candona subtriangulata has been recovered from depths of 45–305 m. Tressler[257] identified Candona decora at a depth of 600 m from Great Slave Lake, Canada. For many limnocytherids, especially Limnocythere ceriotuberosa, and L. staplini, the particle size of the substratum is very important. These ostracodes crawl through the interstices of very fine sand (.0625 mm) to coarse sand (1.0 mm). In these niches, there must be sufficient food and oxygen for survival. Good porosity and permeability of these sediments allows a free flow of oxygenated waters. Most clay-sized, organic-rich sediments are anoxic and reducing and not suitable for ostracodes to live in the interstices.

C.  Physiological and Morphological Adaptations Ostracodes live in a wide variety of habitats, and within a given habitat physical and chemical conditions fluctuate. Physiological adaptations can be seen for some of these changes.

1.  Eggs Dispersal of freshwater ostracode eggs is thought to be passive[153,160,194,198,251] either in the gut or mud on the

feet of birds, particularly for species living in the ­ littoral ­habitat. Eggs which pass through the gut of fish and remain viable assist in passive dispersal[144]. For sampling sites that were up to 1000 km apart, Chaplin and Ayre[32] found no evidence that stream flow was a mediator of short- or long-distance gene flow in (the large green morph of) Candonopsis novaezelandiae.

2.  Resting Stage and Torpidity The primary resting stage for freshwater ostracodes is the egg. The structure of the egg permits the yolk to survive both desiccation and freezing. The other adaptation for surviving harsh conditions in ostracodes is torpidity[6,71,127,182]. Fabaeformiscandona rawsoni has been recovered in the seventh instar from frozen sediments of a pond which had gone dry the previous fall. Placing the sediments in water at room temperature caused rejuvenation of the seventh instar candonids. Survival rate was a function of the moisture content and temperature of the sediments holding the instar at the time of rejuvenation[71]. The major difference was that sediment containing the seventh instar could have a moisture content as low as 4–5%. In the fall or spring, hatching of the eggs and development of the nauplii from the seventh instar may occur. In vernal ponds, torpidity allows sufficient time for the species to become sexually mature and lay eggs. In this way, the species is propagated in temporary bodies of water[273]. The development of the torpid state allows ostracodes to survive the drying of vernal ponds. Horne[127] found a similar situation for Candona patzcuaro, collected from playa lakes of the south plains of Texas.

3.  Coloration Coloration of ostracodes is a function of the pigment bodies located in epidermal cells of both the outer and inner layer. Ostracodes such as Cypridopsis, Cypris, Bradleystrandesia, Eucypris, Herpetocypris, Potamocypris, and Tonnacypris are normally green, although Cypridopsis vidua and Bradleystrandesia may be found in shades of brown and purple. These genera are all prevalent in littoral areas of lakes and in ponds where there is abundant vegetation. Green[103] investigated the green coloration of Eucypris virens and found it to be a bile pigment, biladienes, derived from blue-green algae. Other species, such as Cypricercus horridus and Cypriconcha alba, are purplish to reddish-brown in color, which allows them to blend better with an organic substratum. Mbahinzireki et al.[174] found that marked coloration increased predation risk by fish. The majority of the other species are a dirty white to yellowish-buff color, which blends in with the mineral substrata. Candonids, cyprinotids, and limnocytherids fall into the last category.

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Ecology and Classification of North American Freshwater Invertebrates

4.  Appendages The first and second antennae are modified in swimming ostracodes. Finely feathered swimming setae on the first antennae are in constant motion and offer resistance to the water when the ostracode is swimming. Setae on the second antennae are used in a rowing motion. When the swimming setae are absent, the second antennae are used exclusively for walking and climbing. In the male of some species, the maxillae (formerly referred to as the first thoracic leg) is modified as a prehensile palp. This changes the appendage from a feeding function to a sexual function.

D.  Behavioral Ecology A considerable literature has developed regarding the ecology of ostracode reproductive behaviour for both marine and nonmarine taxa. The marine myodocopid lineages are well known for their bioluminescence, in which visual signaling with flashing light patterns are an important stage in mate recognition[40,192]. In the case of nonmarine taxa, bioluminescence has not been reported, but other mate recognition methods occur. Bonaduce and Danielopol[21] reported that males of Notodromas (Cypridoidea) have enhanced visual capability compared with the female, while the female is strongly pigmented. Horne et al.[124] reviewed of reproductive behavior in nonmarine ostracodes.

E.  Foraging Relationships The diet of most ostracodes is restricted to algae (phytophilic) and organic detritus. Klugh[143] reported certain algae as being part of the food supply. Kesling[135] indicated that diatoms are a part of the ostracode diet as did Strayer[246] for Cypria turneri. Grant et al.[101] reported feeding Cyprinotus carolinensis the blue-green algae Nostoc sp. Campbell[28] calculated that tree pollen made up 8% and organic material 42% of the diet for Australocypris insularis. Tabacchi and Marmonier[252] used Chara with alterable amounts of periphyton covering the stems as did Roca et al.[211]. When feeding, organic particles are swept into the mouth using the maxillae. The mandibular teeth grind large organic particles into a smaller size before they enter the mouth. Although ostracodes are predominantly herbivores and detritivores, a few have shown carnivorous characteristics[131]. Ostracodes have been observed attacking and eating the soft tissue of certain snails[75,76,240]. Some species (Cypridopsis hartwigi, C. vidua, Cypretta kawatai, and Cyprinotus incongruens) are known from experiments, by the above authors, to eat the soft tissue of snails such as the mantle, antennae, and crawl into the respiratory organs.

Have[113] used Paramecium sp. as a source of food by Eucypris sp. in experiments on effects of area and patchiness on species richness. Campbell[28] provided detailed information on the preying habits of Australocypris insularis. These large ostracodes feed on smaller ostracodes, Diacypris compacta and D. dietzi. She also found that this large species grouped around drowned bee carcasses, presumably feeding on them with terrestrial invertebrate detritus making up 8% and insects 3% of the diet. The trophic position of most ostracodes is that of a herbivore and detritivore. This group of benthic animals scavenges and consumes organic matter primarily from the sediment–water interface. Some of this food is fresh, while the remainder is in the process of decaying. During the feeding process, nutrients and the more resistant cellulose and silica (diatom frustules) are moved back into the food chain. Ostracodes are in turn consumed by higher animals. Predators include bottom-dwelling fish. There are several references to the presence of ostracodes in the gut of fishes. Ostracodes have been found in the stomachs of suckers and trout[19,85,109]. Stomach contents of brook stickleback contained Cyclocypris ampla, that of yellow perch had Candona ohioensis, and bullheads had Cypridopsis vidua and Physocypria globula (L. D. Delorme, unpublished data). Griffiths et al.[105] reported the presence of Ostracoda in the guts of arctic charr, Salvelinus alpinus, and the three-spine stickleback, Gasterosteus aculeatus[77]. Bataille and Baldassarre[7] investigated three prairie potholes (near the Delta Waterfowl Research Station, Manitoba) as to the availability of aquatic organisms (including ostracodes) as high protein food for ducks such as mallards and canvas backs. The relative spacing of bill lamellae of specific duck species influenced their selection of different orders of invertebrates[8,197]. Green[102] noted that the oligochaete Chaetogaster diaphanus eats ostracodes as do cyclopoid copepods[96] and the tanypodine midge[210]. Benzie[16] indicated a negative association between a predatory mite and Herpetocypris reptans. Swüste et al.[248] showed experimentally that the phantom midge Chaoborus flavicans released Cypria immediately after capturing it. This suggests that this ostracode either tastes bad or releases a noxious chemical. Lancaster and Robertson[149] looked at the preying habits of the polyphagous net-spinning caddisfly (Plectrocnemia conspersa) and the alderfly (Sialis fuliginosa). They found that the larvae of both flies had very high densities of ostracodes in their guts probably because both groups are very abundant in leaf litter of slow-moving streams. The introduction of fish into a pond, where larger predators have been absent, quickly reduces the invertebrate populations. Martens and de Moor[168] found that the invertebrate populations that lived in a large predator-free habitat were adapted to living in such an environment. The consequence is these habitats will not be repopulated with the same invertebrate populations.

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F.  Population Regulation: Habitat Suitability Abundance of ostracodes at the sediment–water interface is a function of substrata, availability of food, season, and depth of water. Strayer[246] provided a useful and current summary of abundance and biomass measurements of ostracodes in lake environments. Bechara[9] indicated that floodplain lakes with high floating plant biomass had a decrease in biomass during high water periods, with Ostracoda and Oligochaeta as dominants. The presence of food clearly has an impact on species richness and abundance. Long periods of warm temperatures down to the bottom of the euphotic zone favor ostracode production. The numbers of species and specimens recovered from the profundal sediment–water interface are small. For example, the ostracode assemblage in the deep troughs (190– 365 m) of eastern Lake Superior is limited to Candona subtriangulata. At these depths, during the last week in May and the first week in June, the bottom water temperature varied between 2.6 and 4.0°C. Estimates for North America of ostracode diversity and species richness (the number of individual species per sample) within habitats show considerable variability. Based on Canadian habitats sampled for ostracodes (L. D. Delorme, unpublished data), a maximum of nine genera were counted from one sample. In these samples, between 13 and 19 species were represented with a maximum of nine species being alive at the time of collection. The NANODe database records a lake with a maximum of 10 genera and 17 species alive at time of collection[93]. Rouch and Danielopol[219] defined high species diversity for ostracodes as “species collections of more than 25 species within an inventoried area, at the local scale (i.e. between 1 and 100 m length)...”; low diversity was defined as “1-5 species and medium level diversity is 6-24 species.” King et al.[140] found species richness varied up to 13 species per pond. Baltanás[5] attempted to make a comparison between samples using species numbers referred to a fixed sampled area. He evaluated three methods for estimating species richness (the number of individual species per sample) using computer simulations. These were the “Stout and Vandermeer method” based on the species-area relation; the “Cohen method” which assumes the lognormal distribution of species abundances; and the “jackknife method,” a nonparametric procedure with no distributional assumptions. The author[5] found that the estimators tested showed a negative bias, with the second-order jackknife method giving the best results with the highest accuracy and with the best precision. Actual data on dispersal rates of nonmarine ostracodes are not common; however, a study by Havel et al.[114] on the colonization of disturbed habitats following flooding shows that ostracode genera Cypricercus (now Bradleystrandesia), Cypridopsis, Cyprinotus, and Eucypris, along with a rich fauna of zooplankton, ­rapidly

colonize new habitats within 2 years. The source of ­ostracodes in this case was the egg bank, the supply of dormant resting eggs that are capable of hatching after an extensive diapause.

G.  Toxicity of Herbicides and Pesticides Compared with other aquatic microorganisms, ostracodes have not been used to any great extent as biomonitors and sentinels. Ostracodes do represent, however, an untapped resource in this field. Their general habitat preferences are strongly influenced by the physical parameters of temperature, major ion composition, and total concentration, and therefore different species can be selected for study that are specific to the aquatic conditions one wishes to examine. Recently, abundance and diversity of ostracode species assemblages have been studied to examine changes in water quality in streams[188,190], lakes[106], and springs and shallow groundwater habitats[191,201,252]. These studies have employed multivariate statistics such as Canonical Correspondence Analysis and Detrended Correspondence Analysis to show how distinct assemblages of species are associated with different field conditions such as pH, dissolved oxygen, alkalinity, salinity, nitrite, nitrate, and ammonia. Studies of individual species, such as Heterocypris incongruens, have shown that particular ostracode species are useful in sublethal toxicity tests of contaminated sediments[35,118]. Smith et al.[232] analyzed the NANODe database[93] with the purpose of determining which common taxa could be chosen as biomonitors, and determine that Fabaeformiscandona rawsoni, Physocypria globula, and Cavernocypris wardi would be suitable taxa to choose as biomonitors, being widely distributed, abundant, easily identified, and easily collected. Sanders[221] tested Cypridopsis vidua and five other crustaceans against 16 herbicides. Irritability and excitability were the first noticeable reactions. Cypridopsis vidua could only be tested at low concentrations because the animal would close its shell when it received the stimulus. This species was the second most sensitive to the herbicides. Landis et al.[150] found a similar pattern when testing ecological risk assessment of Cyprinotus sp. and other organisms in a microcosm against the water-soluble fraction of jet fuel A. Dieter et al.[79] tested several invertebrates in microcosms at the edge of lakes for toxicity to insecticides. They found that ostracodes were resistant to phorate. Takamura and Yasuno[253] found that ostracodes in rice fields decreased in numbers with a treatment of pesticide mixture of propoxur, thiobencarb, and simetryne. There were similar decreases in ostracodes with a treatment of bentazone. In another rice field, they used a mixture of methomyl, kasugamycin-hydrochloride, neoasozin, thiram, and benomyl with some decrease in ostracode fauna.

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H.  Parasitism More studies are now documenting the role freshwater ostracodes play in parasitism. Dezfuli[77] detailed the effects of the helminth Neoechinorhynchus rutili on the ostracode Cypris reptans (now Herpetocypris). Between 8.6 and 14.5% of this species were infected with up to three larvae found in one host (up to six worms)[280]. The effect of this parasitism is a reduction in the number of eggs contained in females, 103 as compared to 207 in uninfected females. Cypridopsis vidua has been found to be the intermediate host of Neoechinorhynchus prolixus (B. B. Nickol, Univ. Nebraska, personal communication). Cypridopsis sp. acts as a second intermediate host for the parasite Halipegus occidualis[280]. For the complete cycle, eggs from the worm pass through the feces of the green frog (Rana clamitans) and are ingested by the pulmonate snail, Helisoma anceps, while in H. anceps sporocysts and redia stages develop, ending in the development of cercariocysts. Feeding activity of Cypridopsis sp. transfers the cercaria body into the hemocoel of the ostracode. Odonate naiiads eat the affected ostracodes and in turn are eaten by green frogs. Griffiths and Evans[104] found the infestations of the peritrich Nüchterleinella corneliae on Cypria ophtalmica and Cyclocypris ovum. Infestations were more prevalent during winter and decreased during the summer. The parasite tended to be clustered around the bases of the appendages, particularly the genitalia and the furcae. Bronnvall and Larsson[25,26] described new microsporidian parasites Flabelliforma ostracodae and Binucleospora elongata in the ostracode Candona sp. Their investigations, based on light microscopic and ultrastructural characteristics found the musculature, the frequent site for the development of microsporidia, was undisturbed. The infection was restricted to the adipose and connective tissues and to the hemocytes which appeared to be filled with spores. Diarra and Toguebaye[78] examined sections of ostracodes infected by Nosema stenocypris which revealed that the microsporidium develops particularly in the muscles of Stenocypris major, which are destroyed and replaced by the developmental stages of the parasite.

I.  Paleoecology and Paleolimnology With a suitable chronology and age model, the paleolimnology of a pond or lake may be reconstructed from the fossils extracted from a sediment core. Initially, subjective interpretations were made of past conditions of the lake or pond[15,107,193,243,244]. As autecological databases were generated, paleointerpretive models were developed which used autecological data for objective reconstruction of the chemical and physical aspects of the habitat[3,15,42,56,57,63,64,67,69,7274,123,132,133,141,175,202,233,234,269,270]. Forester et al.[91] devised two interesting indices which estimate the TDS (total dissolved solids) ratio of

e­ vaporation to outflow of a large lake and a shore-zone ratio which gives an indication of the proximity of the shoreline to the core site. In each case, ostracode abundances are used in the ratios. Curry[41] devised two environmental tolerance indices (ETI) based on 341 modern aquatic environments in the United States. Trace element analyses of Mg, Ca, and Sr in ostracode shells have been used for reconstructing past salinity changes in a variety of aquatic habitats[3639,52,53,148]. Similar studies are being carried out on North American ostracode shells. Engstrom and Nelson[80] found that distribution coefficients (KD) for (Mg2/Ca2)H2O and (Sr2/Ca2)H2O in shells of Candona rawsoni from cultured samples and from shells collected from Devils Lake, North Dakota, have similar ratios. Analyses show that excess Mg is incorporated into the shell during early calcification, which is a confirmation of the work done by Chivas et al.[38]. Hu et al.[128] traced element analyses of ostracode shells from a sediment core of Farewell Lake, Alaska. From the Mg/Ca and Sr/Ca ratios, they detailed the climatic reconstruction of the area indicating cold and warm climate periods. A 19-m core from Coldwater Lake, North Dakota, documented several century-scale changes in the paleoenvironmental record using 18O, 13C, Mg/ Ca, and Sr/Ca ratios[277]. A total of seven phases of climate and salinity were identified. Yu and Ito[279] using Candona rawsoni shells from a Rice Lake, North Dakota core determined Mg/Ca ratios showing periods of salinity and aridity. Oxygen isotope studies of calcitic shells are being used to develop paleoclimatic interpretations[264,265]. Middle Holocene ostracodes of Elk Lake, Grant County, Minnesota, show an assemblage dominated by Limnocythere staplini, a halophyte. This species is a highsalinity form, yet the oxygen isotope values on shells of Candona rawsoni indicate a decrease by 2–3 ppt indicating that groundwater mediated the paleoclimatic record[234]. Xia et al.[275,276] have determined that calcitic shells of Candona rawsoni formed at temperatures of 15°C and 25°C were not in isotopic equilibrium with water but had a constant offset from equilibrium based on oxygen isotope fractionation of about 2 ppt. With the molting process occurring from spring to fall, the intra-annual temperature change would exceed the interannual to century-scale variations expected during late Quaternary climate shifts. The resulting intra-annual signal may exceed the long-term paleoclimatic signals. The authors suggest 10–15 shells per sample be analyzed to ameliorate the interannual noise.

IV.  EVOLUTION AND PHYLOGENETICS The bivalved calcite shell of ostracodes has provided the means of preserving the group’s extensive fossil record in sedimentary rocks. Indeed for biologists and

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p­ aleobiologists, the ostracode record is a remarkable global archive of evolutionary and ecological information. Recent examination of 18S ribosomal DNA[278] from four extant orders strongly suggests that the ostracode orders were established in Cambrian time, although an unequivocal fossil record of marine ostracodes begins later, in Ordovician time (approximately 450 mya).(Although taxonomic discussion continues regarding the Cambrian phosphatocopines, a taxonomic group once included within the Ostracoda, they are no longer linked to the group based upon recent analysis of appendages[229].) The fossil record of taxa is traceable to origins in Carboniferous deposits (approximately 300 mya)[157], but genetic studies indicate that the three major superfamilies of the Podocopida that house the taxa have been separate for 450 (Ordovician) to 360 (Devonian) million years[229]. An overview of the age and phylogeny of ostracodes is presented in Martens et al.[169] and is briefly summarized here. Based on the fossil record, the Cytheroidea emerged about 450 mya, whereas the Cypridoidea originated in Devonian time (about 400 mya). The Darwinuloidea also first appeared in the Devonian, around 360 mya. All three lineages originated as marine taxa. The invasion of continental habitats did not begin until the late Paleozoic, but the Cypridoidea expanded with an explosive radiation beginning in midJurassic time (approximately 150 mya). Numerous invasions occurred over geologic time, with the consequence that at least for the Cypridoidea and Cytheroidea, monophyletic lineages of nonmarine taxa are unlikely[169].

A.  Molecular Phylogeny Recently, the increase in genomic studies has impacted our understanding of ostracode phylogeny, but the position at the moment is still very much in the crucible. Although ostracodes provide a rich fossil record and have abundantly occupied aquatic habitats since the Paleozoic, taxonomic controversies complicate the attempts to reconstruct phylogenetic histories[126]. In a recent phylogenetic study of first appearances of major ostracode families for which 18S rDNA data are available, Tinn and Oakley[255] reported that fossil estimates and molecular estimates of divergence times for most lineages are incongruent. The authors hypothesized that this lack of agreement is due primarily to taxonomic disagreements at the higher levels of classification, and possibly to homoplasy, or nonhomologous similarities in the fossilized carapaces. An important factor is the erratic rate for molecular evolution of 18S rDNA demonstrated in the lineages examined by Tinn and Oakley[255], suggesting that lineage-specific rate variability may be an important consideration. At this writing, controversy continues regarding the phylogenetic trees based on 18S rDNA data, and the reader is referred to that literature[126,226,227,255,278].

B.  Cladistics The problem of homoplasy in fossil carapaces has led to controversies over cladograms produced using carapace characteristics, and little consensus has been reached. A recent cladistic analysis using exclusively morphological soft part characteristics of 16 extant ostracode superfamilies was carried out by Horne et al.[126], and this produced statistically supported results (bootstrap values) for some lineages but not for the podocopids. Taken together, these studies suggest the possibility that the Ostracoda are polyphyletic, but new analyses remain to be done once key taxonomic controversies are settled.

V.  COLLECTING, REARING, AND PREPARATION FOR IDENTIFICATION A.  Field Collection Ostracodes are not typically caught in a plankton tow or trap, and over the years this has led to the incorrect notion that ostracodes are a rare component of the aquatic habitat. They do not move in a vertical plane, nor are they typically swimming or floating in open water in the middle of a lake, and thus most plankton traps will not collect them. Instead, ostracodes are either benthic swimmers, epibenthic or infaunal, or interstitial. They typically show a patchy distribution, and so assumptions cannot easily be made about their population density. Depending on the habitat (lentic, lotic, or interstitial), different sampling strategies are required. Ostracodes are often living in the hydrated soils, on mosses, charophytes, and among the roots of cattails and bullrushes in fen (alkaline dominant) wetlands[232], even if there is no standing water present. These can be collected easily by collecting sediment and plant samples, or if the sediment is slightly submerged, by using a D-frame net with an attached collecting bottle. The net openings should be between 100 and 150 m (Fig. 19.11a). Surber samplers and D-frame nets with attached collecting bottles are most useful in collecting ostracodes from rheocrene springs. It should be noted that often springs occur within a lacustrine setting, and these sites can frequently be identified along the lakeshore by examining the vegetation. Stands of bullrushes or charophyte thickets are indicators of groundwater discharge, and a temperature probe is a simple method of confirming groundwater seepage into the lake. Often, after heavy rains, springs linked to shallow unconfined groundwater may show higher rates of flow, and these are opportunities to collect individuals that have been flushed out of the sediment matrix by higher flow velocities. Within lakes, ostracodes are most commonly found in the littoral zone, in the sediment and water column around submerged aquatic vegetation. However, in large, deep,

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Ecology and Classification of North American Freshwater Invertebrates

oxygenated lakes, one can expect to find populations of benthic species at considerable depth (e.g., they are living throughout the Great Lakes). The Ekman dredge or Hongve sampler are most useful for deep lake benthos sampling (Fig. 19.11c,e), and both provide a constant sampling area for a quantitative assessment of species, whereas a D-frame net is most useful in the littoral zone. For lessaccessible areas, the Bola pipe fitted with a screen or a net is useful (Fig. 19.11b), because it can be swung out a considerable distance and drawn back in to shore, collecting a sampling of the benthic taxa. For small, shallow ponds, and temporary pools or puddles, a sampling device based on a common entomologist exhauster can be used that will not disturb the sediments[263]. Ostracodes occur in aquifers and can be retrieved by sieving the water as it is pumped from the aquifer. It must be remembered that aquifer ostracodes are small (0.5 mm), and so it is important to use a sieve with small openings (e.g., 63 m mesh). This sieve can be protected from damage by placing a sieve above it with a larger diameter opening. Although much of stream habitat sampling strategy focuses on the riffles rather than the pools as diversity hotspots, ostracode diversity in streams tends to be higher in the pools. For flowing water, D-frame nets (Fig. 19.11a) with attached collecting bottles and Surber samples are useful, as long as the mesh openings on the net are between 100 and 150 m. If using a D-frame net, tap the sediment surface lightly and allow the current to carry material into the net or collecting bottle. It is important to collect some of the sediment, because many species will be encountered within the first 2 cm below the surface of the sediment. The dynamic environment of the stream includes groundwater discharge and recharge, and these areas are the entry and exit points for ostracodes. One important area of the stream, where groundwater and surface water mix in the subsurface, is the hyporheic zone. The hyporheic zone is an important ecotone that can produce an ostracode fauna that is often different from that of the surface water and requires different collecting methods[100]. Although piezometer nests are invaluable for determining the potentiometric surface and the changes in water level, pumping them tends to produce very few ostracodes; and for that reason, a Bau-Rauch pump is recommended for hyporheic ostracode sampling[22,99]. Hyporheic sampling can be done most successfully using a Bau-Rauch pump (Fig. 19.11g) in the downstream side of the sand-gravel of point bars or riffles, where subsurface water is most likely to discharge. Most adult ostracodes and many late instars can be caught on a sieve with 150 m pores, but some smaller adults may slip through. All ostracodes can be caught on a sieve with 63 m openings. A considerable volume of water must be pumped in order to draw up a few ostracodes from this aquatic ecotone, and numerous studies indicate that

s­ amples on the order of 5 L will be needed in order to pull ostracodes from the subsurface zone beyond the immediate area of the pump[23,24,159]. Not surprisingly, the grain size of the sediment will make a considerable difference to the pumping experience. Although the pump may be inserted most easily in finer grained sediment, the yield will be far less and possibly nothing at all, as transmissivity through the sediment will be low. The streambank storage can be sampled as well with the Karaman–Chappuis method[159] of simply digging a hole, allowing it to fill with seepage water, and then collecting the water and a small amount of sediment with a handheld sampler (such as a turkey baster) or with a peristaltic pump.

B.  Sample Preparation Depending on the study goal, different preparation techniques are typically used. If samples are fixed with formalin, it is important to note that formalin is acidic and will dissolve the calcite in ostracode valves. Therefore, if formalin is to be used, it should be buffered with sodium bicarbonate (baking soda). Martens[166] recommended adding 20 g/L sodium bicarbonate, and Malard[159] suggested a buffered 7–10% formalin solution. Upon return from the field, samples may be preserved in ethanol for later dissection, or gently washed through a stack of sieves (8-inch diameter standard brass sieves, sizes (850, 150, and 63 m), and freeze-dried for permanent storage as dry specimens

A

G

C

F D

E

B Figure 19.11  Field equipment for collecting nonmarine ostracodes: (A) D-frame net with collecting jar; (B) Bola pipe with net (also can be made with a screen); (C) Hongve sediment sampler; (D) ordinary turkey baster for siphoning water; (E) Ekman dredge for sediment sampling; (F) minipiezometer for shallow groundwater prospecting; (G) Bou–Rouch pump for sampling the hyporheos of streams.

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Chapter  |  19  Ostracoda

in vials or micropaleontology slides. Dissection and ­mounting techniques are described elsewhere[47,51,157,186]. If ostracodes are to be collected for genetic work of any kind, specimens must be preserved in ≥95 of 100% ethanol. Although this high ethanol concentration preserves genetic material well, the effect on the animals is to cause death with the valves tightly closed, which hampers dissection. Lower concentrations of ethanol (10–30%) will cause death with the valves slightly open or gaping, making dissection easier, but samples stored in this concentration will not be useful for genetic work. If samples are to be used for isotopic or trace metal analysis, they should be clean and dry, and only undamaged specimens should be selected. Close microscopic examination of the shells should be done to ensure that there are no crystalline overgrowths or adhering sediments. Dry specimens should be separated by species and if possible by instar, and placed in vials using a dry brush. A long published history of collection methodologies has pointed, in particular, to methods to avoid: (1) formalin or formaldehyde for storing specimens; (2) drying specimens still within sediment in a drying oven; (3) using a sonicator to clean sediments from valves; and (4) mixing glycerin with formaldehyde if storing specimens on a slide. In all four cases, the specimens will be damaged or ruined.

C.  Rearing Techniques Cosmopolitan ostracodes, such as Cypridopsis vidua and Heterocypris incongruens, are relatively easy to rear in an aquarium. Collection of water, from the habitat associated with the species to be reared, along with some of the substrate will allow the population to develop. Natural water from the habitat is preferred to distilled or tap water. Habitat water contains the proper mix of major and minor ions for an established solute composition. The pH of the water should be checked periodically and adjusted when necessary. This type of aquarium will probably go “wild” and anoxic after several months. A more pristine culture can be set up by filtering the water from the habitat and placing it in an aquarium with sterilized silt, sand, and clay as substrata. Cultured algae[101,118,135,143,211,212,221,280] have been used for food as well as fresh leaf lettuce and grated boiled egg which has been allowed to decompose bacterially for a month. Roca and Wansard[212] also used benthic algae, gastropod pellets, and Spirulina with a high survival rate, whereas chopped alfalfa as food with garden compost produced the lowest survival rate. Schmit et al.[223] showed in controlled experiments that Eucypris virens preferred the cyanobacteria Tolypothrix tenuis as a food source over seven other different materials, and Tolypothrix also provided a substrate for eggs and molting. Aquaria should not be placed on a window ledge where high temperatures

may destroy the artificial habitat. Culture experiments for the purpose of isotopic and trace metal assessment require a strictly controlled temperature regime, and a discussion of these methods can be found in Xia et al.[275].

VI.  IDENTIFICATION OF NORTH AMERICAN NONMARINE OSTRACODES Ostracodes are typically identified from adult specimens. Insufficient information is obtained from the instars (juveniles) to make a proper identification to the species level unless a monoculture has been obtained and adults are present, although exceptions do occur. Some juveniles have sufficiently distinctive carapace proportions and features to make identification possible, as in the case of Cytherissa lacustris or Fabaeformiscandona rawsoni. In many instances, identification of the instar can be taken to the generic level. The most useful biocharacters in taxonomy and systematics are the shell, the appendages, and the reproductive organs. A field key is offered by Delorme[55] for some of the North American ostracode species as well as his five-part series[5862]. Other useful references for North America are Furtos[97] and Hoff[120], and two relatively permanent Internet sites: NANODe (Forester et al.[93]) at www.kent.edu/NANODe, which contains photographic images of the carapaces, along with biogeographic maps and hydrochemistry, and www.ostracoda. nhm.org, the website designed by Mark Angelos at the Natural History Museum of Los Angeles County, which contains detailed images of appendages and keys, and photographic images of carapaces. A European publication that is indispensable for taxonomic and biogeographic information is that of Meisch[186]. Finally, it is important to note that the international research community of ostracodologists is an active one, and can be engaged in discussion through the Internet on a relatively permanent server site that has been active for at least a decade[129].

A.  About the Taxonomic Keys Representatives of Darwinuloidea, Cypridoidea, and Cytheroidea, the three podocopid superfamilies with nonmarine taxa, occur throughout North America. The three keys presented here include photographic images of fifty commonly encountered species representing these groups. Images were taken in reflected and transmitted light using a binocular dissecting microscope so that pigments, valve features, and overall carapace appearance will appear as similar as possible to the features under observation by an aquatic biologist examining a recent sample. Arrows in photographs indicate the anterior direction unless otherwise noted. Some species are strongly sexually dimorphic, and in such cases, the gender is indicated on the image.

746

Ecology and Classification of North American Freshwater Invertebrates

A preliminary examination of the ostracode specimen under study should quickly identify the superfamily to which it belongs (see Section VI.B). In most cases, features carefully observed in the carapace are sufficient to identify many common taxa to the species level, but confirmation can be sought by examining major attributes of the body as well. For this reason, these keys are designed to be dichotomous. These should aid in identifying common taxa to the species level primarily from the carapace characteristics and in providing additional confirmation from readily visible differences in the appendages and/ or reproductive organs.(An exception is the key to the Entocytheridae, which is unchanged from the second edition.) Fifty species, most of them with regional or continental distribution, and including surface water, aquifer, and semiterrestrial taxa, are illustrated as part of these keys. These species were chosen by examining our joint lists of common taxa that were encountered while compiling ostracode databases in Canada and the United States. In using the keys, it is important to keep in mind that the information presented here is necessarily incomplete. Much more detailed information on individual species is available concerning the ostracode body and carapace, but is beyond the goal of this chapter. These sources are referenced within this chapter, and the reader is encouraged to

refer to them as needed. Distribution maps, hydrochemical ranges, and additional images are available as well on NANODe, the North American Ostracode Database[93]. Differences in solute chemistry, temperature, and total ionic concentration (TDS) may play a key role in the distribution of many ostracode species on a regional and continental scale. The reader is encouraged to review the available biogeographical and hydrochemical information about species of interest on this website.

B.  Key to Podocopid Superfamilies in North America The Podocopida is the only order that contains fully nonmarine species. The three superfamilies are strongly represented in North America, with 52–56 genera reported as of 2008 (Table 19.2). Although taxonomic identification can be potentially complex, it is possible to readily identify the superfamily to which an ostracode belongs, and with careful observation of the carapace and some appendages, to identify common taxa. As a first step, the observer should examine the central (adductor) muscle scar pattern on the shell of the ostracode, which will determine the superfamily, and then proceed to the appropriate superfamily key. Examine Fig. 19.3 as you use this key.

1a.

Central muscle scar pattern is a distinct circular rosette. [Confirm: Body with two pairs of walking legs, males unknown to rare.] ............. superfamily Darwinuloidea . ..................................................................................................................................................... (see key VI.C)

1b.

Central muscle scar pattern not a circular rosette ...........................................................................................................................................2

2a (1b).

Central muscle scar pattern is a variable open cluster arranged like a “pawprint,” with scars closely arranged, or more openly arranged. [Confirm: Body with one pair of walking legs, one inverted pair of cleaning legs; males with Zenker’s organs.] . ........................................ superfamily Cypridoidea............................................................................................................................................................ (see key VI.D)

2b.

Central muscle scar pattern is not a variable, open cluster; central muscle scar pattern is a vertically stacked arrangement of four or five scars, some occasionally divided. [Confirm: Body with three pairs of walking legs, no cleaning legs; males without Zenker’s organs, but brushed shaped organs always present.] ................................................................................superfamily Cytheroidea .......... (see key VI.E)

C.  Key to Common North American Species of the Superfamily Darwinuloidea Only one family of this superfamily is extant: Darwinulidae. At present writing, five genera are known, of which three are common in North America (Darwinula, Microdarwinula, and Penthesilenula) and one is rare (Alicenula, reported from Florida (D.G. Smith, 2001) and California (Mark Angelos, personal communication)). The genus Vestalenula has not yet been identified in North America. As the four species currently known from North America are in four different genera, both genus and species are linked in this key. The representatives of Penthesilenula and Alicenula in North America have not been formally described at the time of this writing. Photos of the Darwinulidae in North America are presented in Fig. 19.12a–k. The following is a brief description of the family Darwinulidae: Carapace small (0.4–0.8 mm length),

smooth, white, thinly calcified, vestibules absent, distinctive rosette-shaped adductor muscle scars; first antenna (A1) composed of six podomeres with strong spikelike setae; swimming setae lacking on second antenna; mandibular exopodite with short palp of three podomeres of which the first is wide and has row of long feathered setae; respiratory plate of mandible small; masticatory process of maxilla short and heavy, respiratory plate of maxilla with numerous feathered setae; maxillae with strong masticatory structure and leglike palp of three podomeres; first and second thoracic legs similar in structure and direction, furca lacking; ovaries do not originate between inner and outer epidermis; female carries eggs in posterior of carapace in a brood pouch, usually visible through shell; benthic, infaunal, or interstitial. Members of this family are common throughout North America in most aquatic settings, often in considerable numbers (hundreds) in one locality.

747

Chapter  |  19  Ostracoda

Table 19.2  Classification of nonmarine genera in the class Ostracoda (order Podocopida) occurring in North America** Class Ostracoda Latreille, 1806

  *Genus Pelocypris Klie, 1939

Order Podocopida Sars, 1866

  Family Notodromadidae Kaufmann, 1900

Suborder Metacopina Sylvester-Bradley 1961 (fossil taxa only)

  Subfamily Notodromadinae Kaufmann, 1900

  Suborder Podocopina Sars, 1866

  *Genus Notodromas Lilljeborg, 1853

  Infraorder Sigilliocopina Mandelstam, 1960

  Subfamily Cyproidinae Hartmann, 1963

  Infraorder Bairdiocopina Grundel, 1967

  *Genus Cyprois Zenker, 1854

  Infraorder Darwinulocopina Sohn, 1988

  Family Cyprididae Baird, 1845

Superfamily Darwinuloidea Brady and Norman, 1889

  Subfamily Cypridinae Baird, 1845

  Family Darwinulidae Brady and Norman, 1889

  *Genus Cypris O.F. Muller, 1776

    ( 5 other families, fossil only)

  *Genus Chlamydotheca Saussure, 1858

  *Genus Darwinula Brady and Robertson, 1885

  *Genus Cypriconcha Sars, 1926

  *Genus Microdarwinula Danielopol, 1968

  Subfamily Eucypridinae Bronshtein, 1947

  *Genus Penthesilenula Rosetti and Martens, 1998

  Genus Eucypris Vavra, 1891

  * Genus Alicenula Rosetti and Martens, 1998

  Genus Prionocypris Brady and Norman, 1896

Infraorder Cypridocopina Jones, 1901

  Genus Tonnacypris Diebel and Pietrzeniuk, 1975

Superfamily Macrocypridoidea Muller, 1912

  Subfamily Cypricercinae McKenzie, 1971

Superfamily Pontocypridoidea Muller, 1894

  *Genus Bradleystrandesia Broodbakker, 1983

Superfamily Cypridoidea Baird, 1845

  Genus Strandesia Stuhlmann, 1888

  Family Candonidae Kaufmann, 1900

  Subfamily Herpetocypridinae Kaufmann, 1900

  Subfamily Candoninae Daday, 1900

  Genus Herpetocypris Brady and Norman, 1889

  *Genus Candocyprinotus Delorme, 1970

  Genus Psychrodromus Danielopol and McKenzie, 1977

  *Genus Candona Baird, 184

  Genus Ilyodromus Sars, 1894

  Genus Candonocypris, Sars, 1894

  Genus Stenocypria G.W. Muller, 1901

  *Genus Fabaeformiscandona Krstic, 1972

  Subfamily Cyprinotinae Bronshtein, 1947

  *Genus Nannocandona Ekman, 1914

  Genus Cyprinotus Brady, 1885

  *Genus Paracandona Hartwig, 1899

  *Genus Heterocypris Claus, 1892

  *Genus Pseudocandona Kaufmann, 1900

  Genus Hemicypris Sars, 1903

  *Genus Schellencandona (Klie, 1936)

  Subfamily Dolerocypridinae Triebel, 1961

  Subfamily Cyclocypridinae Kaufmann, 1900

  Genus Dolerocypris Kaufmann, 1900

  *Genus Cypria Zenker, 1854

  Subfamily Isocypridinae Rome, 1965

  *Genus Physocypria Vavra, 1897

  *Genus Isocypris G.W. Muller, 1908

  *Genus Cyclocypris Brady and Norman, 1889

  Subfamily Scottinae Bronshtein, 1947

  Genus Candocypria Furtos, 1933

  *Genus Scottia Brady and Norman, 1889

  Family Ilyocyprididae Kaufmann, 1900

  Subfamily Cypridopsinae Kaufmann, 1900

  Subfamily Ilyocypridinae Kaufmann, 1900

  *Genus Cypridopsis Brady, 1867

  *Genus Ilyocypris Brady and Norman, 1889

  *Genus Cavernocypris Hartmann, 1964 (Continued)

748

Ecology and Classification of North American Freshwater Invertebrates

Table 19.2  Continued   *Genus Sarscypridopsis McKenzie, 1977

  Genus Ascetocythere Hart, 1962

  *Genus Potamocypris Brady 1870

  Genus Cymocythere Hart, 1962

  Genus Thermopsis Külköylüoglu,Meisch and Rust, 2003

  Genus Dactylocythere Hart, 1962

  Subfamily Cyprettinae Hartmann, 1964

  Genus Donnaldsoncythere Rioja, 1942

  *Genus Cypretta Vavra, 1895

  Genus Entocythere Marshall, 1903

Superfamily Cytheroidea Baird, 1850

  Genus Geocythere Hart, 1962

  Family Limnocytheridae Klie, 1938

  Genus Harpagocythere Hobbs, III, 1965

  Subfamily Limnocytherinae Klie, 1938

  Genus Hartocythere Hobbs, III, 1970

  *Genus Limnocythere s str. Brady, 1867

  Genus Hobbsiella Danielopol and Hart, 1985

  Genus Paralimnocythere Carbonnel, 1965

  Genus Litocythere Hobbs and Walton, 1968

  Subfamily Timiriaseviinae, Mandelstam, 1960

  Genus Lordocythere Hobbs and Hobbs, 1970

  *Genus Cytheridella Daday, 1905

  Genus Okriocythere Hart, 1964

  Genus Metacypris Brady and Robertson, 1870

  Genus Ornithocythere Hobbs, 1967

  Family Cytherideidae Sars, 1925

  Genus Phymocythere Hobbs and Hart, 1966

  *Genus Cytherissa Sars, 1925

  Genus Plectocythere Hobbs, III, 1965

  *Genus Cyprideis Jones, 1857

  Genus Psittocythere Hobbs and Walton, 1975

  *Genus Perissocytheridea Stevenson, 1938

  Genus Rhadinocythere Hart, 1962

  Family Loxoconchidae Sars, 1928

  Genus Sagittocythere Hart, 1962

  Subfamily Loxoconchinae Sars, 1928

  Genus Saurocythere Hobbs, III, 1969

  *Genus Cytheromorpha Hirschmann, 1909

  Genus Thermastrocythere Hobbs and Walton, 1966

  Family Entocytheridae Hoff, 1942

  Genus Uncinocythere Hart, 1962

  Genus Ankylocythere Hart, 1962

  Genus Waltoncythere Hobbs and Peters, 1978

Representative species presented in the taxonomic keys of this chapter are indicated in boldface and by * **

Comprehensive lists consulted in developing this table include those of McLauglin et al.[181], Meisch[186], ITIS[130], Forester et al.[93], and Delorme[70]. Martens et al.[172] noted 56 nonmarine genera (excluding Entocytheridae) for North America, but these may include estuarine genera not found in inland waters. We list 53 genera here, all found in inland waters.

1a.

Carapace smooth and wedge-shaped in dorsal and lateral view; Rv (i.e., right valve) overlaps Lv (left valve) at all margins, Rv extends slightly beyond Lv anteriorly and posteriorly in dorsal view; muscle scar pattern anterior of center, visible brood pouch; adults 0.65 mm; antennule (A1) six-segmented, with numerous strong setae and claws; Fig. 19.12a–d. . ................Darwinula stevensoni (Brady and Robertson)



[Common in all nonmarine aquatic settings.]

1b.

Carapace smooth and wedge-shaped, subrectangular, or ovoid, either valve overlaps or Lv overlaps; adults 0.65 mm ............................2

2a (1b).

Carapace smooth, ovoid, evenly rounded extremities of equal height in lateral view; Lv overlaps Rv ventrally and dorsally; muscle scar pattern centrally located; no externally visible brood pouch; adults 0.5 mm (0.3–0.45 mm); two small antero and posteroventral internal “teeth” may be visible on interior of left valve; antenna (A2) with two dorsal setae on the first segment, one dorsal and three ventral setae on the second segment; ovoid shape with rosette muscle scar is distinctive, but can be mistaken in cursory inspection for a juvenile candonid; Fig. 19.12e–g ........................................................................................................................... Microdarwinula zimmeri (Menzel)



[Interstitial in wetland sediments, springs, streams, shallow groundwater. Common in these settings.]

2b.

Carapace smooth, wedge-shaped or subrectangular in lateral view; either valve overlaps or Lv overlaps; muscle scar pattern anterior of center, carapace smaller than 0.65 mm ...........................................................................................................................................................3

3a (2b).

Carapace smooth, wedge-shaped in dorsal and lateral view; Lv overlaps Rv in ventral view, 0.4–0.5 mm length; left valve with anteroand posteroventral internal teeth; muscle scar pattern anterior of center; carapace smaller than 0.65 mm; Fig. 19.12h–k ............................. ................................................................................................................................................................................................... Penthesilenula



[Common in interstitial in wetland sediments, springs, streams, shallow groundwater.]

749

Chapter  |  19  Ostracoda

3b.

Either valve overlaps; carapace smooth, subrectangular in lateral view; muscle scar pattern anterior of center; carapace smaller than 0.65 mm . ........................................................................................................................................................................................... Alicenula



[Reported from Florida and California.]

D.  Key to Common North American Species of the Superfamily Cypridoidea The superfamily Cypridoidea comprise the majority of nonmarine species living today, and these ostracodes are mostly active swimmers. Although most have well-

A

d­ eveloped natatory setae on the antennules and antennae (A1 and A2), some species no longer have natatory setae and instead live infaunally, interstitially, or as part of the epibenthos, such as the members of the Candoninae. Four families are represented in North America: Candonidae, Ilyocyprididae, Notodromadidae, and Cyprididae.

B

C D

G E

F

J

H

I

K

Figure 19.12  (A–K) Darwinulidae. Darwinula stevensoni (Brady & Robinson, 1890): (A) left valve, (B) left valve, (C) dorsal view, (D) central muscle scar rosette. Note overlap of Rv over Lv. Specimens from littoral benthos, East Twin Lake, Ohio. Microdarwinula zimmeri Danielopol, 1968: (E) dorsal view, (F) right valve, (G) left valve. Note overlap of Lv over Rv, central muscle scar rosette. Specimens from interstitial fen sediments, Mantua Bog, Ohio. Penthesilenula sp. Rosetti & Martens, 1998: (H) dorsal view, (I) ventral view, (J) left valve, (K) left valve interior, showing antero and postero ventral internal teeth (arrows). From interstitial sediments, Herrick Fen, Ohio.

750

Ecology and Classification of North American Freshwater Invertebrates

The following is a brief description of the superfamily Cypridoidea: surface of the shell usually smooth or ­punctate, dorsal margin without interlocking teeth; size and shape of carapace variable, with strong sexual dimorphism in some genera; eyes developed to varying degrees, either separated or fused into a single median eye; first antennae with basal portion of two or three podomeres and an endopodite of four or five podomeres, with s­wimming setae usually well developed; second antennae with basal part of two podomeres and an endopodite of three or four podomeres; exopodite is reduced to a small scalelike appendage bearing at most three setae; maxillula not pediform but modified as a mouthpart,

with the anterior margin of the base adapted for feeding; maxillar endopodite forms a small palp in the female but is enlarged to form prehensile palps in the male; first thoracic leg has an endopodite of three or four podomeres and a strong ­ distal claw; second leg is bent dorsally and is probably used in cleaning the respiratory surfaces and other parts of the body; second leg usually has three distal setae but the distal end may be modified for grasping; furca is ­ typically well developed and rod-shaped but may be reduced to a flagellum or whiplike structure; gonads are located within the valves of the shell; in males a portion of the vas deferens is modified to form an ejaculatory duct, the Zenker organ.

1a.

Central adductor muscle scar pattern a tight “pawprint” arrangement of three anterior scars, two posterior scars, and a cap of one ­elongated scar; valve size and shape variable, smooth or pitted; second antenna (A2) natatory setae present, reduced, or absent . ............... family Candonidae.........................................................................................................................................................................................31

1b.

Central adductor muscle scar pattern an open cluster with elongate scars .....................................................................................................2

2a (1b).

Carapace subrectangular, with one or two sulci, surface pitted, sometimes with nodes or alae; left valve overlaps right valve in ventral view, natatory setae on (A2) reduced or well developed; duplicature narrow, vestibules weakly developed . family Ilyocyprididae .......... 3

2b.

Carapace not subrectangular, no sulci, duplicature narrow to wide, vestibules developed ............................................................................5

3a (2a).

Carapace with two sulci, surface pitted, sometimes with alae; Zenker’s organ with 15–20 spines (Meisch[186], p. 244), size range 0.8–0.9 mm . ........................................................................................................................................................................Ilyocypris .......... 4

3b.

Carapace with two sulci, surface deeply pitted with large nodes and tubercles, especially on margins; third thoracic leg terminates in a pincer, genus Pelocypris; second antenna (A2) with swimming setae; third thoracic leg terminates in two setae and a pincer, Fig. 19.4d–f . ............................................................................................................................................... Pelocypris alatabulbosa Delorme

4a (3a).

Second antenna (A2) reduced or rudimentary, valves pitted but without tubercles or nodes on lateral surface; third thoracic leg ends in seta. Fig. 19.13a–c ........................................................................................................................................................ Ilyocypris bradyi Sars

4b.

Second antenna (A2) with well-developed swimming setae, valves pitted and usually with alae, but size and prominence of these varies (not pictured) ..........................................................................................................................................................Ilyocypris gibba Ramdohr

5a (2b).

Carapace thinly calcified, glassy, smooth, large, and circular to ovoid (1–1.5 mm) in side view, compressed or tumid in dorsal view, anterior margin in dorsal view with numerous highly visible radial pore canals ............................................... family Notodromadidae .......... 6

5b

Carapace ovoid to elongate ovoid, no sulci, surface smooth, pitted, or occasionally ornamented with small tubercles or spines, cleaning leg (T3) with clawlike pincer ................................................................................................................................ family Cyprididae .......... 7

6a (5a).

Highly compressed in dorsal view, left valve overlapping right valve ventrally, anterior acutely pointed in dorsal view; cleaning leg (T3) terminates in pincer: genus Cyprois (subfamily Cyproidinae); valves subequal in size and shape, highly visible radial striation in anterior margin, many radial pores, female larger (to 1.50 mm in length) than male (about 1.35 mm in length); Fig. 19.14a–c . ................................ ...............................................................................................................................................................................Cyprois marginata (Straus)

6b.

Not compressed, but rounded in dorsal view, venter flat with ridges, allowing animal to cling to underside of water surface; cleaning leg (T3) does not terminate in a pincer; eye cups of adults separated (not fused) and visible under microscope: genus Notodromas (subfamily Notodromadinae); left valve of female has a spatulate caudal process pointed posteriorly; Fig. 19.14d–g ................ Notodromas monacha ..................................................................................................................................................................................................... (O.F. Müller)

7a (5b).

Carapace large (1.5–3 mm in length), smooth, or faintly sculptured; walking leg with four segments . .........subfamily Cypridinae .......... 8

7b.

Carapace less than 1.75 mm in length . .........................................................................................................................................................10

8a (7a).

Carapace inflated and subtriangular in side view and subovate in dorsal view, anterior of left valve margin with a well-developed ridge: genus Cypris; carapace surface rough, with setae; caudal process on Rv consists of 1–3 small spines or denticles; Fig. 19.15e–g. . ............ ....................................................................................................................................................................Cypris pubera............ O.F. Müller



[Strong swimmer, parthenogenetic in North America.]

8b.

Carapace not subtriangular in side view .........................................................................................................................................................9

9a (8b).

Carapace very large (2–6 mm) smooth, elongate oval in side view, with prominent anterior flange, which is more pronounced on right valve, and highly visible in transmitted light: genus Chlamydotheca; anterior flange of RV approx 1/8th length of entire valve; in dorsal view, Lv extends beyond Rv anteriorly, Rv extends beyond Lv posteriorly; Fig. 19.5a,b ..............................Chlamydotheca arcuata (Sars)

9b

Carapace smooth, without prominent anterior flange and not oval in side view; carapace subtrapezoidal to subrectangular in side view, tumid, smooth; dorsum faintly convex, wide anterior and posterior margins, vestibules well developed: genus Cypriconcha; carapace subtrapezoidal in side view, inflated in dorsal view; dorsum straight, venter faintly concave; shell smooth, vestibules well developed; Fig. 19.15c,d ..................................................................................................................................................... Cypriconcha ingens Delorme

10a (7b).

Carapace large (1 mm), smooth, elongate and elliptical in side view, appendage morphology includes “presence of a c-seta on the female maxilliped” (Meisch[186] p. 278) .................................................................................................... subfamily Eucypridinae .......... 11

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Chapter  |  19  Ostracoda

A

C

E

B

D

F

Figure 19.13  (A–F) Ilyocypris and Pelocypris. Ilyocypris bradyi Sars, 1890: (A) left valve, (B) dorsal view. Specimen from littoral benthos, Dead Coon Lake, Minnesota. Ilyocypris bradyi Sars, 1890: (C) right valve. Specimen from littoral benthos, Bullock Pen Lake, Kentucky. Pelocypris alatabulbosa Delorme, 1970: (D) right valve. Specimen from littoral benthos, Bandwell Reservoir, Texas. Pelocypris alatabulbosa Delorme, 1970: (E) left valve, (F) dorsal view. Specimen from benthos of unnamed permanent stream, Saskatchewan. 10b.

Carapace smaller (1 mm or less), c-seta not present on female maxilliped ..................................................................................................13

11a (10a).

Carapace large, elongate oval in side view, dorsal margin angular; both valves have anteroventral denticles; broad duplicature (calcified inner lamellae) ............................................................................................................................................................................. Prionocypris

11b.

Anteroventral denticles absent; carapace elliptical in side view, sometimes elongate; broad duplicature (calcified inner lamellae) ..........12

12a (11b).

Carapace elliptical, tumid, with rounded hump on anteroventral margin of both valves .................................................................. Eucypris

12b.

Carapace elliptical, elongate, smoothly rounded anterior and posterior, tiny blunt tooth present in anteroventral portion of left valve . ....... .......................................................................................................................................................................................................Tonnacypris



[Holarctic distribution.]

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Ecology and Classification of North American Freshwater Invertebrates

A

B

D

C

F

E

G

Figure 19.14  (A–G) Cyprois and Notodromas. Cyprois marginata Straus, 1821. (A) Left valve, (B) right valve. Note distinct radial pore canals in anterior and posterior margins. Specimen from littoral zone, Elkwater Lake, Alberta. Cyprois marginata Straus, 1821. (C) Dorsal view. Notodromas monacha (Muller), 1776: (D) Lv interior view of venter, (E) Lv, ventral view. Notodromas monacha (Muller), 1776. (F) Left valve, (G) right valve. Note spatulate caudal process on female posteroventer. Specimen from Cottonwood Lake, North Dakota. 13a (10b).

Uropod (furca) has a distinct oval to triangular loop, known as the Triebel loop[186]; carapace elongate, wedge-shaped, low dorsal angle; left valve overlaps right valve ventrally; males show spirally coiled seminiferous tubes visible in the anterior portion of the carapace ....... subfamily Cypricercinae................................................................................................................................................................................14

13b.

Absence of a Triebel loop; carapace shape variable .....................................................................................................................................15

14a (13a).

Carapace subtriangular and elongated in side view, with prominent dorsal flange. Left valve always with conspicuous row of tuberclelike canals removed from the free margin ...................................................................................................................................... Strandesia

14b.

Carapace without prominent dorsal flange or tubercle-like canals on left valve; triebel loop is ovate (as compared to triangular shape shown in Bradleycypris[186]): genus Bradleystrandesia (equivalent with Cypricercus); carapace subtriangular and elongated in side view, with distinct overlap of left valve over right valve in anterior in dorsal view; valve surface smooth; in transmitted light, radial pore canals are distinct in ventral margin area. Fig. 19.16e–j ..............................................................................Bradleystrandesia reticulata (Zaddach)

15a (13b).

Carapace elongate, low in height, subrectangular, smooth; base of uropod (furca) supported with a triangular structure; in transmitted light, normal pores and additional conical inclusions[186] visible; marginal pore canals branching or straight and highly visible in

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Chapter  |  19  Ostracoda

A

B

C

D

E

F

G Figure 19.15  (A–G) Chlamydotheca, Cypriconcha, and Cypris. Chlamydotheca arcuata (Sars), 1901: (A) female right valve, (B) female left valve. Note: instars differ markedly in appearance from adult. Specimen from Ash Spring, Nevada. Cypriconcha ingens (Delorme), 1967: (C) male left valve, (D) left valve, female above and male below. Specimens from littoral benthos of Lake Ardock, North Dakota. Cypris pubera O. F. Müller, 1776: (E) female right valve, (F) female right valve, (G) dorsal view. Note caudal processes with one to three short spines. Specimens from littoral zone of Rome Lake, Wisconsin and an unnamed pond, Alberta. transmitted light; natatory setae on second antenna (A2) well developed . ......................................................................................subfamily Herpetocypridinae..........................................................................................................................................................................................16

[Cosmopolitan.]

15b.

Absence of a triangular supporting structure at base of uropod (furca) .......................................................................................................18

16a (15a).

Carapace elongate in lateral view, dorsal margin straight; in dorsal view, carapace moderately compressed; left valve overlaps right valve; large, about 1.5–2.6 mm in length, radial pore canals visible in transmitted light; posterior seta of the uropod small[186]; color typically green . ................................................................................................................................................................................Herpetocypris

16b.

Dorsum not straight but arched, inner lamellae expanded anteriorly, marginal pore canals narrow; posterior seta of the uropod well developed or transformed to a spine .............................................................................................................................................................17

17a (16b).

Carapace elongate, dorsal margin arched; calcareous inner lamellae expanded anteriorly and posteriorly, narrow marginal pores; posterior seta of the uropod well developed . ........................................................................................................................................ Stenocypria

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Ecology and Classification of North American Freshwater Invertebrates

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E D

F

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I

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J

Figure 19.16  (A–J) Isocypris and Bradleystrandesia. Isocypris quadrisetosa Rome, 1947. (A) Left valve, (B) left valve anterior showing distinct radial pores, (C) dorsal view. Specimen from littoral zone, High Point Lake, Pennsylvania. Isocypris quadrisetosa Rome, 1947. (D) Left valve. Bradleystrandesia reticulata (Zaddach, 1844): (E) left valve, (F) right valve, (G) dorsal view. Note Lv overlaps Rv. Bradleystrandesia reticulata (Zaddach, 1844). (H) Left valve, (I) right valve view of venter, (J) left valve view of venter. Specimen from littoral zone of Elkwater Lake, Alberta.

17b.

Carapace elongate, dorsal margin arched; calcareous inner lamellae expanded only anteriorly, narrow marginal pores; posterior seta of the uropod “transformed to a spine” (Meisch[186] p. 322) .......................................................................................................Psychrodromus

18a (15b).

Denticles (variously reported as pustules, tubercles) on anteroventral edge of right or left valve; carapace plump to tumid, dorsal margin strongly arched, valves asymmetric ............................................................................................................subfamily Cyprinotinae .......... 19



[Cosmopolitan.]

18b.

No denticles on anteroventral edge of right or left valve . ............................................................................................................................21

19a (18a).

Stout, elongate oval in side view, strongly arched dorsal margin; denticles (tubercles) present along posteroventral margin of left valve; valves symmetrical . ....................................................................................................................................................................... Hemicypris

19b.

Denticles present on anteroventral of right valve, not on left valve .............................................................................................................20

20a (19b).

Stout, elongate oval in side view, strongly arched dorsal margin; denticles (tubercles) present along posteroventral margin of right valve; in dorsal view, a hump is visible on right valve ..............................................................................................................................Cyprinotus

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Chapter  |  19  Ostracoda

A

B

C

D

E

F

G

Figure 19.17  (A–G) Heterocypris and Scottia. Heterocypris incongruens (Ramdohr, 1808). (A) Left valve, (B) left valve, (C) dorsal view. Specimen from littoral zone of Alkali Lake, California. Heterocypris incongruens (Ramdohr, 1808) (D) view of posteroventral edge of right valve showing row of denticles. Scottia pseudobrowniana Kempf, 1971. (E) Right valve, (F) right valve, and (G) Dorsal view. Specimen from hydrated wetland soil, Mantua Bog, Ohio. 20b.

No hump present on right valve: genus Heterocypris; stout, elongate oval in side view, with asymmetrical valves; in dorsal view, anterior is narrowly rounded, posterior broadly rounded; surface smooth, wide inner lamellae visible in anterior of shell in transmitted light; ­reddish-brown in color; Fig. 19.17a–d . ................................................................................................Heterocypris incongruens (Ramdohr)



[Note: Heterocypris and Cyprinotus are very similar, differing in minor carapace features (the hump on the right valve) and small ­differences in appendages. Meisch[186] provided an overview of these differences.]

21a (18b).

Carapace extremely narrow, greater than 1 mm in length, with height less than half the length; inner lamellae very broad anteriorly and posteriorly, surface smooth, right valve overlaps left valve at both ends ....................................................................................Dolerocypris



[Holarctic distribution.]

21b.

Carapace not extremely narrow, both anterior and posterior inner lamellae not broad ................................................................................22

22a (21b)

Carapace subrectangular in side view, about 1–1.3 mm in length, laterally compressed in dorsal view; shell is thinly calcified, glassy, with numerous setae; anterior margin with distinct, large radial pores visible in transmitted light, anterior inner lamellae broad, with expanded vestibule; posterior margin shows two extra long setae: genus Isocypris; carapace thin, translucent, hirsute; surface smooth with faint reticulation visible in transmitted light over the posterior third of the carapace; prominent anterodorsal notch above the eye; Fig. 19.16a–d. ....................................................................................................................................................Isocypris quadrisetosa Rome

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Ecology and Classification of North American Freshwater Invertebrates

22b.

Carapace not subrectangular or laterally compressed, and less than 1 mm in length ...................................................................................23

23a (22b).

Carapace small (0.6–0.7 mm), stout, smooth, ovate in lateral and dorsal view, anterior and posterior evenly rounded; first thoracic leg with one long terminal seta and claw; uropod (furca) with terminal claws and one long seta; left valve overlaps right valve ventrally, can be hirsute; semiterrestrial in wetlands: genus Scottia; carapace stout and ovate in lateral view, anterior and posterior ends broadly rounded, venter concave, dorsal margin arched. In dorsal view, carapace ovate and tumid; left valve overlaps right valve in anterodorsal region with a tab or semicircular expansion; valve surface smooth, thickly calcified, often with numerous setae; color mottled brown and green; Fig. 19.17e–g ....................................................................................................................................Scottia pseudobrowniana Kempf



[Semiterrestrial on fen wetland soils, leaf litter, and mosses.]

23b.

Carapace small (0.3–0.7 mm), dorsal margin strongly or weakly arched, variably shaped ovoid to crescent in side view, ovoid to circular in dorsal view ................................................................................................................................................................................................24

24a (23b).

Fused portion anterior margin very broad, visible in transmitted light; uropod (furca) reduced, without terminal claw ................................ subfamily Cypridopsinae...............................................................................................................................................................................25

24b

Conspicuous marginal septa in the anterior and posterior margins, visible in transmitted light: subfamily Cyprettinae; carapace strongly arched in side view, almost circular in dorsal view. Anterior margins each with row of radiating septa: genus Cypretta; surface covered in reticulations like a fingerprint in transmitted light. Fig. 19.18h–j ............................................................. Cypretta brevisaepta Furtos, 1934

A

B

C

D

E

F

G

H

I

J

Figure 19.18  (A–J) Cavernocypris, Potamocypris, and Cypretta. Cavernocypris wardi Marmonier, Meisch, & Danielopol, 1989: (A) left valve, (B) right valve, (C) dorsal view, (D) ventral view. Note Lv overlaps Rv in ventral view. Specimens from Ledge Spring, Nevada. Potamocypris unicaudata Schäfer, 1943: (E) right valve, (F) left valve, (G) left valve. Note Rv vaulted over Lv dorsally, Rv extends beyond Lv anteriorly, Lv extends beyond Rv posteriorly. Specimen from littoral zone of West Stump Lake, North Dakota. Cypretta brevisaepta Furtos, 1934: (H) right valve, (I) right valve, (J) dorsal view. Note tumid shape in dorsal view and “fingerprint” sculpturing in transmitted light. Specimen from littoral zone of Shickshack Sand Pond, Illinois.

Chapter  |  19  Ostracoda

757



[Note: The genus Cypretta is large and cosmopolitan. For North America, the reader is encouraged to examine the work of Furtos[143], in which many species were originally described.]

25a (24a).

Carapace shows left valve overlapping right valve in ventral view ..............................................................................................................26

25b.

Carapace shows right valve overlapping left valve in ventral view ..............................................................................................................28

26a (25a)

Carapace ovate in side and dorsal view, dorsal margin arched gently or steeply; in dorsal view, carapace is widest in center, and may be tumid; natatory setae on second antenna (A2) well developed; color banding pronounced with 3–5 transverse greenish brown stripes, numerous tiny pits visible in transmitted light . .............................................................................................................. Cypridopsis..........27

26b.

Carapace elongate crescent shape in side view, dorsal margin arched; in dorsal view, carapace compressed: genus Cavernocypris; ­natatory setae on second antenna (A2) strongly reduced; color white, shell smooth; Fig. 19.18a–d . ............................................................. ...............................................................................................................................Cavernocypris wardi Marmonier, Meisch and Danielopol



[Hyporheos, springs, seeps, and pumped from aquifers.]

27a (26a).

Carapace narrow oval in side view, dorsal margin gently arched; in dorsal view, carapace is widest in center, not tumid; radial pore canals extremely visible in transmitted light, pitting on valves is faint; Fig. 19.19a–c .................................. Cypridopsis okeechobei Furtos

27b.

Carapace wide oval in side view, dorsal margin strongly arched; in dorsal view, carapace is widest in center, tumid; pitting on valves is pronounced in transmitted light; Fig. 19.19d–f ............................................................................................ Cypridopsis vidua (O.F. Müller)

28a (25b).

Carapace subreniform in side view, light green in color ...............................................................................................................Thermopsis



[Occurring in hot springs in Nevada in a temperature range of 46–51°C[116].]

28b.

Carapace subtriangular to crescent shaped, and not occurring in hot springs ..............................................................................................29

29a (28b).

Carapace subtriangular in side view, dorsal margin strongly arched; in dorsal view, slight sinuation in anterodorsal margin because valves are slightly different in shape; valve surface covered in pits and tiny punctae, often with numerous setae, giving a slightly granulated effect; Fig. 19.19g–i ........................................................................................................................... Sarscypridopsis aculeata (Costa)



[Saline prairie potholes and saline lakes.]

29b.

Carapace subtriangular to crescent-shaped in side view, valves strongly asymmetric, with one valve extending beyond the another anteriorly or posteriorly ........................................................................................................................................................Potamocypris.......... 30

30a (29b).

Carapace crescent-shaped in side view, dorsal margin strongly arched; right valve vaulted over left valve dorsally, right valve extends beyond left valve anteriorly; left valve extends beyond right valve posteriorly; well-developed posteroventral flange visible on left valve in transmitted light; color green. Fig. 19.18e–g . ....................................................................................... Potamocypris unicaudata Schafer

30b.

Carapace crescent-shaped in side view; left valve overlaps right valve in dorsal view anteriorly and posteriorly with a distinct flange; hirsute, with long setae oriented toward posterior; color green, often with darker green banding (not pictured) . .......................................... ...................................................................................................................................................................... Potamocypris smaragdina Vavra



[Note: Many species of Potamocypris occur in North America, and the reader is encouraged to examine Delorme[279] and Meisch[10] for details on this group. Valve overlap is an extremely important taxonomic feature of the group.]

31a(1a).

Natatory setae on second antenna (A2) absent; carapace white to yellow-orange or translucent, strong sexual dimorphism common . ........ subfamily Candoninae...................................................................................................................................................................................32



[Benthic, interstitial, and infaunal.]

31b.

Natatory setae on second antenna (A2) present, often well developed. Carapace thinly calcified, color brown to transparent, can be patterned .................................................................................................................................................... subfamily Cyclocypridinae .......... 45

32a (31a).

Carapace stout, broadly and equally rounded in side and dorsal view, surface heavily reticulated with ridges and tiny papillae, creating a granulated or “sugared” appearance in reflected light, network of reticulations highly visible in transmitted light; only one species known from North America; Fig. 19.20a–c . .......................................................................................... Paracandona euplectella Robertson



[Stream hyporheos, springs, seeps.]

32b.

Carapace not broadly and equally rounded in side and dorsal view . ...........................................................................................................33

33a (32b).

Carapace very small (0.4–0.5 mm) and trapezoidal, with straight dorsum; compressed in dorsal view; surface covered in small pits; white, with no eye pigment visible; North American species undescribed at present; Fig. 19.20d–f ................................Nannocandona sp.



[Pumped from aquifers and present in rheocrene karstic springs.]

33b.

Carapace without straight dorsum, size variable ..........................................................................................................................................34

34a (33b).

Carapace very small (0.4–0.5 mm) triangular in side view, with asymmetrical valves, left valve triangular, right valve trapezoidal; left valve has a flattened protuberance along the dorsal margin, similar to Schellencandona triquetra described in Europe; North American species undescribed at present; white, with no eye pigment; surface covered in small pits. Fig. 19.20g–i ....................Schellencandona sp.



[Pumped from aquifers and present in rheocrene karstic springs.]

34b.

Carapace not triangular, size variable ...........................................................................................................................................................35

35a (34b).

Carapace short and high and broadly rounded to trapezoidal in side view, compressed in dorsal view; setae that stand out away from surface may be numerous; left valve overlaps right valve ventrally; surface of juveniles often pitted, then smooth in adult stage; wide anterior inner lamellae: genus Pseudocandona; carapace reniform in side view, greatest height slightly more than half the length; inner lamellae wide anteriorly, narrow otherwise; dorsal margin straight, posterior end higher and more broadly rounded than anterior; in dorsal view, carapace laterally compressed, left valve overlaps right valve anteriorly and posteriorly . ........... Pseudocandona stagnalis (Sars)

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Ecology and Classification of North American Freshwater Invertebrates

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E

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Figure 19.19  (A–I) Cypridopsis and Sarscypridopsis. Cypridopsis okeechobei Furtos, 1936: (A) left valve, (B) left valve, (C) dorsal view. Note flattened dorsal arch and reduced height compared to other cypridopsids. Specimens from rheocrene springs, Mantua Bog, Ohio and Herrick Fen, Ohio. Cypridopsis vidua (Müller), 1776: (D) left valve, (E) left valve, (F) dorsal view. Specimen from subaquatic vegetation in littoral zone, East Twin Lake, Ohio. Sarscypridopsis aculeata (Costa, 1847): (G) right valve, (H) left valve, (I) dorsal view. Note numerous raised punctae. Specimen from littoral zone, West Stump Lake, North Dakota.

[Note: The Candoninae are a diverse group and a subject of considerable taxonomic complexity and controversy[43,60,97,120,130,186]. This genus is distinguished from Candona and Fabaeformiscandona on the basis of detailed differences in the cleaning leg (T3). According to Meisch[186], p. 152, “basal segment with 3 setae, medial seta of penultimate segment always missing, terminal segment with one short and two long setae.” The reader should be aware that many North American species that probably belong in this group have not yet been reexamined and transferred from the genus Candona. Two that have been transferred are Pseudocandona albicans and P. stagnalis.]

35b.

Carapace not trapezoidal in side view, not compressed in dorsal view, and not exhibiting numerous perpendicular setae . .......................36

36a (35b).

Carapace elongate and reniform in side view, with posterodorsal margin steeper than anterodorsal margin, and height greatest at about two-thirds the length; broad in dorsal view, greatest width close to midpoint; smooth, white to yellowish orange, sometimes transparent; males with an anteroventral notch in carapace ........................................................................ Candona and Fabaeformiscandona .......... 37

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Chapter  |  19  Ostracoda

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Figure 19.20  (A–I) Paracandona, Nannocandona, Schellencandona. Paracandona euplectella Brady & Norman, 1889: (A) left valve, (B) right valve, (C) dorsal view. Note reticulate pattern with numerous papillae. Specimens from hyporheic zone, Pomme de Terre River, Minnesota and groundwater seep, Mantua Bog, Ohio. Nannocandona sp. Ekman, 1914. (D) Left valve, (E) right valve, (F) dorsal view. Note reticulate pattern and flat dorsum. Specimens from karstic rheocrene Priest Spring, West Virginia. Schellencandona sp. (Klie, 1936). (G) Left valve, (H) left valve, (I) right valve. Note asymmetrical valves with trapezoidal Rv vaulted over Lv. Specimens from karstic rheocrene Clip Mill Spring, West Virginia.



[Note: Candona and Fabaeformiscandona are distinguishable taxonomically only by detailed dissection of the mandibular palp. According to Meisch[186],p.57, “the externo-distal seta (gamma seta) of the penultimate segment of the mandibular palp is plumose within the genus Candona, smooth in all other candoninae genera.” The reader should be aware that many North American species that may belong in the genus Fabaeformiscandona have not yet been reexamined and transferred from the genus Candona. Two that have been transferred are Fabaeformiscandona rawsoni and Fabaeformiscandona caudata (photos shown in this key).]

36b.

Carapace ovoid and stout in side view, inflated in dorsal view, with anterior inner lamellae tipped inward and with concentric striations; no natatory setae on second antenna (A2); no males known from North America; one species of this genus is known from North America; Fig. 19.21d–g ..............................................................................................................................Candocyprinotus ovatus Delorme

37a (36a).

Carapace large (1.6–2 mm in length), elongate reniform in side view, narrow but not compressed in dorsal view, anterior acutely pointed; shell surface smooth, although textured appearance of posterolateral surface appears in transmitted light; males always present; Fig. 19.21a–c ..........................................................................................................................................................Candona ohioensis Furtos



[Permanent lakes.]

37b.

Carapace less than 1.6 mm ............................................................................................................................................................................38

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Ecology and Classification of North American Freshwater Invertebrates

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G

Figure 19.21  (A–G) Candona ohioensis and Candocyprinotus. Candona ohioensis Furtos, 1933: (A) female right valve, (B) male left valve. Note that late instars are comparable in size to adults of other candonid species. Specimens from benthos, East Twin Lake, Ohio. Candona ohioensis Furtos, 1933: (C) right valve, female above and male below. Specimens from East Twin Lake, Ohio. Candocyprinotus ovatus Delorme, 1970: (D) dorsal view. Specimen from unnamed intermittant stream, Saskatchewan. Candocyprinotus ovatus, Delorme, 1970: (E) female right valve, (F) female left valve, (G) female left valve. Specimen from unnamed intermittant stream, Saskatchewan. 38a (37b).

Carapace elongate reniform in side view, narrow but not compressed in side view; shell smooth; left valve of female with extreme posteroventral caudal process that may be sharp or blunted; in dorsal view, left valve clearly overlaps right valve; males always present; Fig. 19.22a–d ..................................................................................................................................Fabaeformiscandona caudata Kaufmann

38b.

Carapace without extreme posteroventral caudal process ............................................................................................................................39

39a (38b).

Carapace elongate reniform in side view, narrow but not compressed in dorsal view, anterior acutely pointed; in side view, female posterior dorsal margin is squared to form obtuse angle with venter; shell smooth; males always present; Fig. 19.23a–d . ................................... ..........................................................................................................................................................................................Candona acuta Hoff



[Permanent lakes and streams.]

39b.

Carapace without squared posterior dorsal margin forming obtuse angle with venter on female . ..............................................................40

40a (39b).

Carapace stout reniform in side view, dorsum convex and smoothly arched; ventral margin concave; anterior and posterior broadly rounded; in dorsal view, carapace is wide; female with posterodorsal flange on left valve, which may be pronounced or somewhat ­flattened; males strongly arched, carapace has a “cashew” shape in side view; shell smooth, white to yellowish orange, normal pores pronounced in transmitted light; males always present; Fig. 19.22e–h ........................................... Fabaeformiscandona rawsoni (Tressler)



[Prairie potholes, wetlands, and also lakes.]

40b.

Carapace without posterodorsal flange on left valve in females ..................................................................................................................41

41a (40b).

Carapace large (approximately 1.5 mm) subquadrate in side view, dorsum convex and steeply arched, with greatest height posterior of center, venter concave; posterodorsal line steep, posteroventral angle acute; posterodorsal margin gently sloping in male, posterior

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Chapter  |  19  Ostracoda

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A

B D

E

G

F

H

Figure 19.22  (A–H) Fabaeformiscandona caudata and F. ­ rawsoni. Fabaeformiscandona caudata (Kaufmann, 1900): (A) right valve, female above, male below, (B) dorsal view, female left, male right, (C) male left valve, (D) female left valve. Specimens from Dead Coon Lake, Minnesota. Fabaeformiscandona rawsoni (Tressler, 1957) Griffiths, 1995: (E) female right valve, (F) female left valve. Note caudal process on Female Lv varies in size. Specimens from benthos of Lake Norden, South Dakota. Fabaeformiscandona rawsoni (Tressler, 1957) Griffiths, 1995: (G) male left valve, (H) right valve, female above, male below. Specimens from benthos of Steep Bank Lake, Minnesota.

rounded; in dorsal view, greatest width posterior of center; smooth, white to yellowish orange; males always present; Fig. 19.23e–g . ....... .......................................................................................................................................................................... Candona crogmaniana Turner

[Springs, seeps, lakes.]

41b.

Carapace not subquadrate, and without combined steep posterodorsal margin and acute posteroventral angle in female . ........................42

42a (41b).

Carapace stout reniform to subovate in side view, dorsum convex and evenly arched; posterodorsal margin steep, posteroventral margin narrowly rounded; in dorsal view, carapace is wide, with anterior acutely pointed and posterior broadly rounded; ventral margin concave; smooth, white, with distinct normal pores visible in transmitted light; males very rare; Fig. 19.23h–j ........................................... ........................................................................................................................................................................Candona candida (O.F. Müller)



[Cosmopolitan, holarctic.]

42b.

Carapace without combined steep posterodorsal margin and narrowly rounded posteroventral margin in female .....................................43

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Ecology and Classification of North American Freshwater Invertebrates

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A

B D

F

E G

H

I

J Figure 19.23  (A–J) Candona acuta, C. crogmaniana, and C. candida. Candona acuta Hoff, 1942: (A) female right valve posterior, (B) right valve, female above, male below, (C) female right valve, (D) male right valve. Specimen from littoral benthos, East Twin Lake, Ohio. Candona crogmaniana Turner, 1894: (E) right valve, female above, male below, (F) female left valve, (G) male left valve. Specimens from benthos and springs in Page Pond, Ohio. Candona candida Müller, 1776: (H) female right valve, (I) female right valve, (J) female dorsal view. Specimens from Little Twin Lake, Washington and Elkwater Lake, Alberta.

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Chapter  |  19  Ostracoda

A

B

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E

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F

H

I

Figure 19.24  (A–I) Candona decora, C. distincta, and C. elliptica. Candona decora Furtos, 1933: (A) female left valve, (B) male right valve, (C) right valve, female above, male below. Note faint reticulation on posterolateral portion of female shell. Specimens from littoral benthos, Little Twin Lake, Washington. Candona distincta Furtos, 1933: (D) female left valve, (E) male left valve, (F) right valve, female above, male below. Note sinuation in dorsal hinge line. Specimens from littoral benthos, East Twin Lake, Ohio and Rome Pond, Wisconsin. Candona elliptica Furtos, 1933: (G) male left valve, (H) female left valve, (I) left valve, female above and male below. Specimens from littoral benthos, East Twin Lake, Ohio. 43a (42b).

Carapace subtriangular to wedge-shaped in side view, thinly calcified, posterior of shell inflated in side view with strong arch and steep posterodorsal margin, subtruncate; in dorsal view, valves compressed; female has posterolateral reticulation (faint) on carapace best seen in transmitted light, otherwise carapace is smooth; transparent, thin shell; males always present; Fig. 19.24a–c .......................................... .....................................................................................................................................................................................Candona decora Furtos



[Temporary ponds, vernal pools.]

43b.

Carapace not inflated in side view with strong arch, not subtruncate ..........................................................................................................44

44a (43b).

Carapace subtriangular in side view, greatest width posterior of center; dorsal margin subtruncate, with strong sinuation in dorsal hinge line in female, giving a pronounced humped appearance; shell surface white, smooth except for faint reticulation in posterolateral portion of female best seen in transmitted light; Fig. 19.24d–f ....................................................................................Candona distincta Furtos



[Temporary ponds, permanent lakes.]

44b.

Carapace not subtriangular and without strong sinuation in dorsal hinge line; carapace elongate subreniform to oval in side view, sides subparallel, dorsum evenly convex; posterior narrowly rounded in female, broadly rounded in male; inner lamellae wide anteriorly, narrow otherwise; male greater in length and height than female; shell smooth, white; Fig. 19.24g–i ........................Candona elliptica Furtos



[Temporary ponds, seeps, lakes.]

45a (31b).

Carapace oval to round in side view, thinly calcified and transparent, moderately to very compressed in dorsal view, row of denticles on anterior of right valve, valves unequal in outline; second antenna (A2) natatory setae extremely long; shell pigmented with large brown irregular spots ................................................................................................................................................................Physocypria ..........46

45b.

Carapace oval to round in side view, but without row of denticles on anterior of right valve, and not pigmented with large brown ­irregular spots ..............................................................................................................................................................................................................47

46a (45b).

Carapace oval, with row of denticles along ventral margin of right valve; valves meet without significant overlap on dorsal margin, and with slight overlap of left valve in anterior; cosmopolitan; Fig. 19.25a–d .......................................................... Physocypria globula Furtos



[All shallow aquatic habitats, prefers subaquatic vegetation.]

46b.

Carapace oval, with row of denticles along anterior margin of right valve; valves meet with large overlap of left valve over right valve dorsally and anteriorly; cosmopolitan, all shallow aquatic habitats, prefers subaquatic vegetation; Fig. 19.25e–h ........................................ .......................................................................................................................................................................... Physocypria pustulosa Sharpe

764

Ecology and Classification of North American Freshwater Invertebrates

A

C

B

D E

F

G

H

Figure 19.25  (A–H) Physocypria. Physocypria globula Furtos, 1933. (A) Left valve, (B) right valve, (C) right valve. Note slight overlap of anterior Lv. Specimens from littoral subaquatic vegetation, East Twin Lake, Ohio. Physocypria globula Furtos, 1933. (D) Rv view of denticles on venter. Physocypria pustulosa Sharpe, 1897. (E) Rv view of denticles on anteroventral margin. Physocypria pustulosa Sharpe, 1897. (F) Left valve, (G) right valve, (H) right valve. Note strong overlap of Lv over Rv dorsally and anteriorly. Specimens from littoral subaquatic vegetation, East Twin Lake, Ohio.

47a (45b).

Carapace oval in side view, valves meet evenly; sides almost parallel in dorsal view, very compressed; brown speckled coloration; Fig. 19.26g–i ......................................................................................................................................................... Cypria ophtalmica (Jurine)



[Cosmopolitan, all shallow aquatic habitats, prefers subaquatic vegetation.]

47b.

Carapace ovate in side view and high, with inflated to tumid appearance in dorsal view; marginal area of valves marked by fused zone with a semicircular to crescent-shaped expansion, visible in transmitted light; natatory setae of second antenna (A2) well developed; valves are shiny light to dark brown ............................................................................................................................. Cyclocypris .......... 48



[Note: Several species of Cyclocypris occur in North America. The reader is encouraged to examine the works of Delorme[59] and Meisch[186] for a detailed overview of this group.]

48a (47b).

Carapace strongly convex in side and dorsal view; tumid, with broadly rounded posterior; venter convex; 0.5 mm, ranging from 0.55 to 0.76 mm in length; dark brown and shiny, with normal pores visible in transmitted light; Fig. 19.26a–c ............. Cyclocypris ampla Furtos

48b.

Carapace ovate in side view and dorsal view, not tumid; right valve overlaps left valve anteriorly and posteriorly, and ventrally; venter flat to faintly concave; color light brown, shiny, with highly visible normal pores in transmitted light; smaller than C. ampla, ranging in size from about 0.4 to 0.5 mm; Fig. 19.26d–f ........................................................................................................ Cyclocypris ovum (Jurine)

765

Chapter  |  19  Ostracoda

A

B

C

D

E

F

G H I Figure 19.26  (A–I) Cyclocypris and Cypria. Cyclocypris ampla Furtos, 1933: (A) right valve, (B) left valve, (C) dorsal view. Specimens from Rome Pond, Wisconsin and Barney Lake, Beaver Island, Michigan. Cyclocypris ovum (Jurine), 1820: (D) left valve, (e) right valve, (F) dorsal view. Specimens from an unnamed intermittent stream, Alberta, and the littoral zone of West Lost Lake, Minnesota. Cypria ophthalmica (Jurine), 1820: (G) right valve, (H) right valve, (I) dorsal view. Note lateral compression in dorsal view, and brown flecked coloration in life. Specimen from subaquatic vegetation in littoral zone of East Twin Lake, Ohio.

E.  Key to Common North American Species of the Superfamily Cytheroidea The superfamily Cytheroidea is a large and mostly marine group which contains three families that include nonmarine taxa: the Limnocytheridae, the Cytherideidae, and the Entocytheridae. All three families have representatives in North America, and occur in fresh to hypersaline

conditions. In addition, saline inland lake habitats also occasionally support Cytheromorpha, a genus in the otherwise marine family Loxoconchidae. The members of the Cytheroidea cannot swim and have three pairs of walking legs that often show sexual dimorphism. The following is a brief description of this superfamily: shell variable in shape and sculpturing, seldom smooth, usually with reticulations, often with spines, furrows, or

766

Ecology and Classification of North American Freshwater Invertebrates

tubercles; shells noncalcareous in the Entocytherinaes; valves nearly equal, often with toothlike projections along the hinge; first antennae consist of a base of two podomeres and an endopodite of three or four podomeres; setae of the first antennae are short and stout, often clawlike; exopodite or the flagellum of the second antennae is represented by a long hollow seta forming a duct carrying secretions from a gland; endopodite of the second antennae of three podomeres, the long penultimate one may be divided; swimming setae lacking; maxillar endopodites and two pairs of thoracic legs similar and all

adapted for crawling except in the Entocytherinae modified for grasping; furca always greatly reduced; hemipenes of males always present and well developed, the Zenkers organs are absent, a male accessory sense organ (brush-shaped organs) consisting of numerous setae on a short base is located between and somewhat medially to the bases of the first and second pairs of thoracic legs; gonads do not lie between the inner and outer lamellae of the valves but are in the body lateral to the intestine; eggs in some species are retained in the shell cavity during development.

1a.

Free-living, entirely benthic species with carapace surface reticulated and ornamented with sulci and/or nodes, sexual dimorphism commonly pronounced in carapace shape, inner lamellae of valves strongly calcified; walking legs T1–T3 with long terminal claw ...............2

1b.

Commensal or ectoparasitic on crayfish, shrimp, or isopods; chitinous, laterally compressed carapace, length less than 0.7 mm; walking legs T1–T3 are short, with a hooklike claw .................................................................................................. family Entocytheridae .......... 11

2a (1a).

Carapace thinly calcified, elongate, reticulate, with one or two dorsal-medial sulci, and tubercles, nodes, and/or alae; no vestibules developed; antenna (A2) angled, with three apical (terminal) claws; free margins showing marginal pore canals; sexual dimorphism pronounced, and males are of greater length than females ...............................................................................family Limnocytheridae .......... 4

2b.

Carapace heavily calcified and without flattened free margins showing marginal pore canals .....................................................................3

3a (2b).

Carapace heavily calcified, variable in shape, reticulated with spines, nodes, sulci, and tubercles, vestibules absent, strong sexual dimorphism; basal segment of walking legs T1 and T2 with a strong, conspicuously ringed seta[186] .....................family Cytherideidae .......... 8

3b.

Carapace heavily calcified, pitted with numerous normal pores, distinct hinge with a single tooth on each valve, one anterodorsally placed and the other posterodorsally placed (known as gongylodont hinge); thoracic legs successively increasing in length: family Loxoconchidae, genus Cytheromorpha; carapace subrectangular, dorsal margin weakly convex, anterior and posterior broadly rounded in side view as well as dorsal view; females shorter and higher than males; shell surface pitted, one faint sulcus, hinge well developed, duplicature narrow; Fig. 19.30d,e ................................................................................................................. Cytheromorpha fuscata (Brady)



[Known only from saline seeps in Lakes Manitoba and Winnipegosis, otherwise marine.]

4a (2a).

Shells subrectangular, reticulate, with two sulci, alae, or pustules on surface, margins may be denticulate, no vestibules developed, flattened free margins showing many short or long radial pore canals, unbranched, especially visible on anterior margin; males longer, more inflated in posterior region than females; strong sexual dimorphism . ...........................................Limnocythere .......... 5 (see a-g for 7 spp)

4b.

Shells subrectangular to ovoid, smooth to reticulate, with one or no sulcus, radial pore canals branching or not visible; females larger and longer than males, strong sexual dimorphism . ........................................................................................................................................6

5a (4a).

Shell subtrapezoidal in side view, heavily reticulate; greatest height posterior of center in male, anterior in female; distinct anteroventral nodal ridge directed toward posterior; bisulcate, with posterior of the two sulci longer and with a raised ridge reentrant along dorsum; Fig. 19.27a–d ........................................................................................................................................Limnocythere ceriotuberosa Delorme



[Benthos of prairie potholes and lakes of western North America.]

5b.

Shell subrectangular in side view, reticulate; bisulcate with posterior of the two sulci longer; dorsum straight to slightly concave; posteroventer subtruncate in male, forming obtuse angle with dorsum; alae (laterodorsal) and nodes (lateroventral) present, and denticles are faintly developed on anterior and posterior margins; Fig. 19.27e–g ................................................................ Limnocythere verrucosa Hoff



[Benthos of lakes in the Great Lakes region, and forested and parkland regions of North America.]

5c.

Shell subrectangular (male) to subtrapezoidal (female) in side view, thinly calcified, reticulate; posterior in lateral view is subtruncate and strongly subtrapezoidal in females, subrectangular and rounded in males; alae present and directed toward posterior, either pronounced and sharp, or subtle and rounded; anterior margin broad, striated, flattened ............................................Limnocythere itasca Cole



[Benthos of lakes in the Great Lakes region, and forested and parkland regions, widely distributed.]

5d.

Shell subrectangular in side view, reticulate, bisulcate; dorsum flat to slightly convex; posterior and anterior broadly rounded in lateral view; anterior is acutely pointed in dorsal view; no alae; no males occur in this parthenogenetic form (see syngamic form Limnocythere sappaensis in this key); Fig. 19.28e–h . .........................................................................................................Limnocythere inopinata (Baird)



[Benthos of streams; ponds and lakes in the interior plains.]

5e.

Shell subrectangular in side view, reticulate, bisulcate; dorsum straight to slightly convex in female, convex in male; no alae; posterior and anterior broadly rounded in lateral view; in male, posteroventral area is expanded; benthos of saline ponds and lakes in the interior plains with a distinct hydrochemical preference for bicarbonate-enriched, high TDS; this is the syngamic form of Limnocythere ­inopinata (see this key) but has such a distinct environmental preference that the name is retained; Fig. 19.28i–k ....................................... ......................................................................................................................................................................Limnocythere sappaensis Staplin

5f.

Shell reniform in side view; reticulate, bisulcate; dorsum convex, humped in female; venter concave, strongly so in male; male is lower in height; no alae; in dorsal view, male is compressed posteriorly; Fig. 19.28a–d ................... Limnocythere staplini Gutentag and Benson

767

Chapter  |  19  Ostracoda

C

A

B D

E

F G

J

H

I K

Figure 19.27  (A–K) Limnocythere ceriotuberosa, L. verrucosa, and L. itasca. Limnocythere ceriotuberosa Delorme, 1967: (A) left valve, female above, male below, (B) dorsal view, female left, male right, (C) female Lv, (D) male Rv. From littoral benthos, Devil’s Lake, North Dakota. Limnocythere verrucosa Hoff, 1942: (E) female left valve, (F) male left valve, (G) right valve, female above, male below. Note posteroventral denticles along margin. From littoral benthos, East Twin Lake, Ohio. Limnocythere itasca Cole, 1949: (H) right valve, female above, male below, (I) dorsal view, male left, female right. (J) Female Rv, (K) male Rv. From Lake Itasca, Minnesota.

[Benthos of saline and hypersaline lakes and ponds of the interior plains with a distinct hydrochemical preference for bicarbonatedepleted high TDS.]

5g.

Shell subrectangular in side view, weakly reticulate, faintly bisulcate; dorsum straight; venter faintly concave, male and female of equal height, male longer; no alae; Fig. 19.29g–i .................................................................................................Limnocythere bradburyi Forester



[Benthos of bicarbonate-enriched saline ponds, ditches, and shallow lakes of southwestern North America and Mexico.]

6a. (4b).

Shell subrectangular in side view, reticulate, one weak sulcus, anterior margin flattened and branching radial pore canals; in dorsal view, subrectangular, anterior is acutely pointed; female larger than male .................................................................................. Paralimnocythere



[Benthos of small ponds, not common; reported from California.]

6b.

No branching radial pore canals, heart-shaped in dorsal view, posterior of female carapace inflated; reticulate, punctate, or smooth, one deep sulcus or no sulcus .................................................................................................................................................................................7

768

Ecology and Classification of North American Freshwater Invertebrates

C

A

B D

F E

G

I

H

J

K Figure 19.28  (A–K) Limnocythere staplini, L. inopinata, and L. sappaensis. Limnocythere staplini Gutentag & Benson, 1962: (A) left valve, female above, male below, (B) dorsal view, female right, male left, (C) female Rv, (D) male Rv. From littoral benthos, West Stump Lake, North Dakota. Limnocythere inopinata (Baird) 1843: (E) left valve, (F) left valve, (G) right valve, (H) dorsal view. Parthenogenetic form. Littoral benthos, Elkwater Lake, Alberta. Limnocythere sappaensis Staplin, 1963. (I) Female left valve, (J) male left valve, (K) left valve, female above, male below. Note this is the syngamic form of L. inopinata (above, this plate). Males appear with increasing salinity and bicarbonate enrichment (see text.) Specimen from Shinbone Lake, North Dakota.

7a (6b)

One deep sulcus, posterior of female strongly inflated; shell subrectangular in side view, heart-shaped in dorsal view, surface punctate or tuberculate: genus Cytheridella; shell surface covered with tiny tubercles visible in transmitted light, adductor scars set on internal ridge and located low on shell, carapace length about 0.75 mm; Fig. 19.30a–c ...........................................................Cytheridella ilosvayi Daday

7b.

No sulcus, shell ovate in side view, heart-shaped in dorsal view, pitted surface; right valve hinge line with one tooth; females larger than males ...............................................................................................................................................................................................Metacypris



[Reported by Tressler[256] from bromeliads in Florida.]

8a (3a).

Carapace ovate to subrectangular in side view, dorsal margin slightly convex, posterior and anterior margin rounded; left valve hinge interior shows numerous pits, left valve larger than right valve; shell heavily calcified; females with inflated posterior to house brood

769

Chapter  |  19  Ostracoda

A B C

D

E

F

G

H

I Figure 19.29  (A–I) Cyprideis, Perissocytheridea, and Limnocythere bradburyi. Cyprideis salebrosa van den Bold, 1963: (A) female right valve, (B) dorsal view, female on left, male on right, (C) left valve, female above, male below. Specimens from littoral benthos, Lake Whitney, Texas. Perissocytheridea bicelliforma Swain, 1955: (D) male left valve, (E) female left valve, (F) left valve, female above, male below. Specimens from unnamed golf course drainage ditch, Houston, Texas. Limnocythere bradburyi Forester, 1985: (G) male right valve, (H) female right valve, (I) right valve, female above, male below. Specimens from Road Forks ditch, New Mexico. chamber; posteroventral spine may be present; one sulcus faintly developed, numerous radial pore canals visible in anterior margin in transmitted light Cyprideis...............................................................................................................................................................................9 8b.

Carapace wedge-shaped, dorsal margin straight, surface reticulate with or without large nodes or ridges, no brood pouch visible, no posteroventral spine . ..........................................................................................................................................................................................10

9a (8a).

Valve surface covered with numerous small pits and tubercles visible in transmitted light; posteroventral spine absent; females exhibit prominent brood pouch, particularly in dorsal view; Fig. 19.29a–c ..........................................................Cyprideis salebrosa Van den Bold

9b.

Posteroventral spine usually present; right valve of male has posteroventral lateral depression; females and males are similar in height, males slightly longer; valve surface covered with numerous small pits and tubercles . ................................. Cyprideis beaconensis (Leroy)

10a (8b).

Valves are thick, reticulate, with up to seven large nodes; carapace is large, with adults reaching lengths of 0.95–1 mm; subrectangular in dorsal view; sieve plate normal pores clearly visible in transmitted light; Fig. 19.30f–h .................................. Cytherissa lacustris (Brady)



[One species known in North America, parthenogenetic; benthos of large, deep lakes.]

770

Ecology and Classification of North American Freshwater Invertebrates

A

B

D

E

F

G

C

H

Figure 19.30  (A–H) Cytheridella, Cytheromorpha, and Cytherissa. Cytheridella ilosvayi Daday, 1905: (A) female right valve, (B) right valve, female above, male below, (C) female Dorsal view. Note strong sexual dimorphism. Specimens from littoral benthos, Pierson Lake, Louisiana. Cytheromorpha fuscata (Brady, 1869): (D) left valve, female above, male below, (E) dorsal view, male left, female right. Specimens from benthos, Lake Manitoba. Cytherissa lacustris Sars, 1925: (F) female right valve, (G) female right valve, (H) female dorsal view. Note that noding is variable. No males known from North America. Specimen from benthos, Lake Erie. 10b.

Valves are reticulate, without nodes, but with ridges and normal pores clearly visible in transmitted light; valves are small, with adults reaching lengths of about 0.5 mm; males are slightly longer than females, but females are greater in height; Fig. 19.29d–f ......................... .............................................................................................................................................................. Perissocytheridea bicelliforma Swain



[One species known from inland waters in North America.]

11a.(1b).

Penis with prostatic and spermatic elements widely separated along much of their lengths .......................................................................12

11b.

Penis simple; or if two elements recognizable, contiguous along their entire lengths .................................................................................14

12a (11a).

Ventral portion of peniferum tapering with tip of penis reaching, or almost reaching, apex .....................................................Plectocythere

12b.

Ventral portion of peniferum usually rounded or with one or more prominences, seldom tapering; if tapering, tip of penis never approaching apex . .......................................................................................................................................................................................................13

13a (12b).

Ventral portion of peniferum rounded, without prominences . ..................................................................................................Phymocythere

13b.

Ventral portion of peniferum with one or more prominences ventrally and/or anteriorly . ....................................................... Ascetocythere

14a (11b).

Penis directed posteroventrally from base .................................................................................................................................. Lordocythere

14b.

Penis directed anteroventrally from base ......................................................................................................................................................15

Chapter  |  19  Ostracoda

771

15a (14b).

Finger guard absent . .....................................................................................................................................................................................16

15b.

Finger guard present .....................................................................................................................................................................................26

16a (15a).

Anteroventral portion of peniferum with acute beaklike projection . ...................................................................................... Ornithocythere

16b.

Anteroventral portion of peniferum never with beaklike projection ............................................................................................................17

17a (17b).

External border of horizontal ramus of clasping apparatus with one or more excrescence .........................................................................18

17b.

External border of horizontal ramus of clasping apparatus entire or with few shallow subapical grooves . ................................................22

18a (17a).

Anteroventral portion of peniferum produced ventrally in rounded lobe .....................................................................................................19

18b.

Anteroventral portion of peniferum never produced ventrally in rounded lobe; or if produced, apex acute or truncate .............................20

19a (18a).

Spermatic loop horizontal, peniferum distal to dorsal margin of spermatic loop at least twice as long as portion dorsal to loop, clasping apparatus with external border bearing single tubercle and terminating in fanlike cluster of serrations ....................................Saurocythere

19b.

Spermatic loop vertical, peniferum distal to dorsal margin of spermatic loop much less than twice as long as portion dorsal to loop, clasping apparatus with external border broadly serrate and terminating in annulations . ..........................................................Okriocythere

20a (18b).

Anteroventral portion of peniferum never with conspicuous anterodorsally directed projection .............................................Ankylocythere

21b.

Anteroventral portion of peniferum with conspicuous anterodorsally directed projection ..........................................................................22

21a (20b).

Anteroventral portion of peniferum entire ..................................................................................................................................... Geocythere

21b.

Anteroventral portion of peniferum bifid ................................................................................................................................... Hartocythere

22a (17b).

Internal border of clasping apparatus with more than three teeth, apical cluster with more than two denticles, vertical ramus straight............................................................................................................................................................................................................23

22b.

Internal border of clasping apparatus usually with no more than three teeth, if more than three, with only two apical denticles or vertical ramus strongly convex posteriorly ................................................................................................................................................................24

23a (22a).

Ventral portion of peniferum tapering to slender tip . ............................................................................................................. Rhadinocythere

23b.

Ventral portion of peniferum never slender nor tapering .............................................................................................................. Entocythere

24a (22b).

Clasping apparatus not clearly divisible into vertical and horizontal rami, extremities directed at angle of at least 100° .............................. ........................................................................................................................................................................................... Donnaldsoncythere

24b.

Clasping apparatus usually divisible into vertical and horizontal rami, extremities directed at angle of no more than 90° ........................25

25a (24b).

Penis large, S-shaped or sinuous and with curved posteroventral thickening of peniferum giving forcipate appearance to ventral portion of peniferum . ..................................................................................................................................................................... Thermastrocythere

25b.

Penis of moderate size, L-shaped, and never so disposed as to contribute forcipate appearance to ventral portion of peniferum .................. ................................................................................................................................................................................................... Uncinocythere

26a (15b).

Peniferum with accessory groove (except in Dactylocythere leptophylax where finger guard is always slender and trifid) . .....................27

26b.

Peniferum without accessory groove; finger guard never slender and trifid ................................................................................................28

27a (26a).

Posteroventral portion of peniferum terminating in barbed point .............................................................................................Sagittocythere

27b.

Posteroventral portion of peniferum variable, but never ending in barbed point .................................................................... Dactylocythere

28a (26b).

Ventral portion of peniferum bulbiform, clasping apparatus never extending so far ventrally as does peniferum .....................Cymocythere

28b.

Ventral portion of peniferum slender or strongly flattened; clasping apparatus extending ventrally to or beyond ventral extremity of peniferum ......................................................................................................................................................................................................29

29a (28b).

Ventral portion of peniferum slender, terminating in small recurved projection . ..................................................................Harpagocythere

29b.

Ventral portion of peniferum flattened and with concave border .................................................................................................. Litocythere

VII. Selected References 58. Delorme LD. Freshwater ostracodes of Canada. Part I: Subfamily Cypridinae. Can J Zool. 1970;48:153–169. 59. Delorme LD. Freshwater ostracodes of Canada. Part II: Subfamilies Cypridopsinae, Herpetocypridinae, and family Cyclocyprididae. Can J Zool. 1970;48:253–266. 60. Delorme LD. Freshwater ostracodes of Canada. Part III: Family Candonidae. Can J Zool. 1970;48:1099–1127. 61. Delorme LD. Freshwater ostracodes of Canada. Part IV: Families Ilyocyprididae, Notodromadidae, Darwinulidae, Cytherideidae, and Entocytheridae. Can J Zool. 1970;48:1251–1259. 62. Delorme LD. Freshwater ostracodes of Canada. Part V: Families Limnocytheridae, Loxoconchidae. Can J Zool. 1971;49:43–64.

  86. Forester RM. The relationship of two lacustrine ostracode species to solute composition and salinity, implications for paleohydrochemistry. Geology. 1983;11:435–439.   93. Forester RM, Smith AJ, Palmer DF, Curry BB. North American Ostracode Database “NANODe” Version 1, http://www.kent.edu/ NANODe, Kent State University, Kent, Ohio, USA; 2005. 158. Maddocks R. Ostracoda. In: Harrison FW, Humes AG, eds. New York: Wiley-Liss Publishing; 1992:415–441. Microscopic Anatomy of Invertebrates, Chapter 9, Volume 9: Crustacea. 165. Martens K. Sex and Parthenogenesis—Evolutionary Ecology of Reproductive Modes in Non-Marine Ostracods. Leiden: Backhuys Publishers; 1998: 335p. 186. Meisch C. Freshwater Ostracoda of Western and Central Europe. Heidelberg, Berlin: Spektrum Akademischer Verlag GmbH; 2000: 522 p.