Epibionts on shells in the Šárka Formation: a sparsely occupied niche in the lower to middle Darriwilian (Oretanian, Ordovician) in the Prague Basin (Czech Republic)

Journal Pre-proof Epibionts on shells in the Šárka Formation: a sparsely occupied niche in the lower to middle Darriwilian (Oretanian, Ordovician) in the Prague Basin (Czech Republic) Ondřej Zicha, Jana Bruthansová, Petr Kraft PII:

S0031-0182(19)30552-8

DOI:

https://doi.org/10.1016/j.palaeo.2019.109401

Reference:

PALAEO 109401

To appear in:

Palaeogeography, Palaeoclimatology, Palaeoecology

Received Date: 6 June 2019 Revised Date:

5 October 2019

Accepted Date: 5 October 2019

Please cite this article as: Zicha, O., Bruthansová, J., Kraft, P., Epibionts on shells in the Šárka Formation: a sparsely occupied niche in the lower to middle Darriwilian (Oretanian, Ordovician) in the Prague Basin (Czech Republic), Palaeogeography, Palaeoclimatology, Palaeoecology, https:// doi.org/10.1016/j.palaeo.2019.109401. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier B.V. All rights reserved.

1

Epibionts on shells in the Šárka Formation: a sparsely occupied niche in the lower to

2

middle Darriwilian (Oretanian, Ordovician) in the Prague Basin (Czech Republic)

3 4

Ondřej Zicha a, Jana Bruthansová b,c, Petr Kraft b*

5 6

a

BioLib, z. s., Jugoslávských partyzánů 34, 160 00, Prague 6, Czech Republic

7

b

Institute of Geology and Palaeontology, Faculty of Science, Charles University, Albertov 6,

8

128 43 Prague 2, Czech Republic

9

c

10

Department of Palaeontology, National Museum, Cirkusová 1740, 193 00, Prague 9, Czech

Republic

11 12

* Corresponding author.

13

E-mail addresses: [email protected] (O. Zicha), [email protected] (J.

14

Bruthansová), [email protected] (P. Kraft)

15 16 17

Key words: Interactions; Substrate; Behavior; Hyoliths; Echinoderms; Monoplacophorans

18 19 20

ABSTRACT

21 22

Epizoic invertebrates attached to shells are a rare component of the fauna of the Šárka Formation

23

(Middle Ordovician; early to middle Darriwilian) of the Prague Basin (Barrandian area) in the

24

Czech Republic. Epibionts are known exclusively from siliceous nodules and consist of

25

echinoderms (edrioasteroids and possible crinoid holdfasts), monoplacophorans, and bryozoans,

26

all attached to a very small number of host taxa. Among them, hyoliths are the strongly preferred

27

substrate (60 % of observed host shells), with edrioasteroids, possible crinoid holdfasts and the

28

monoplacophoran Pygmaeoconus attaching exclusively to these organisms. Epizoan holdfasts

29

were also found on a unique ramose problematic fossil considered to be the first octocoral

30

specimen from the Šárka Formation. Most of the host are interpreted have been colonized during

31

life, only a few shells were used for attachment post mortem. All epibionts are attached to the

32

outer surface of the shell, with the exception of the monoplacophoran Barrandicella, which is

33

attached to the internal surface of empty conulariid thecae. Some of the epibionts shed additional

34

light on the mode of life of their hosts, including the bivalve Redonia, which is shown to be

35

semi-infaunal rather than infaunal. More generally, epibionts in the Šárka Formation attest to a

36

very low level of occupancy of this significant niche during the early stages of the Great

37

Ordovician Biodiversification Event.

38 39 40

1. Introduction

41 42

The shale-dominated Šárka Formation (Middle Ordovician) is one of the most richly

43

fossiliferous stratigraphic units of the Prague Basin (Barrandian area, Czech Republic). Thanks

44

to its taxonomically diverse marine fauna with dominating trilobites, which is well preserved

45

especially in siliceous nodules, the Šárka Formation has been a favorite target of fossil collectors

46

since its first description by Barrande (1856). In spite of the fact that the fauna of the Šárka

47

Formation has been studied in detail, and there are thousands of specimens from this unit in

48

public and private collections, little attention has been paid to specimens occurring as epibionts.

49

More generally, fossil epizoans have been sporadically documented from the Early

50

Paleozoic in the Barrandian area. The oldest known specimens were found in the Cambrian

51

(Drumian) of the Skryje-Týřovice Basin, in the Skryje Member of the Buchava Formation

52

(Nolčová and Mergl, 2016). Small discoid epibionts, attached to shells of brachiopods and

53

hyoliths as well as trilobite fragments, were originally interpreted as edrioasteroids but later

54

reinterpreted as eocrinoid holdfasts (Zamora et al., 2017). All other discoveries are from the

55

Prague Basin, from strata ranging in age from Ordovician to Middle Devonian, though the

56

remainder of this overview deals only with epibionts from Ordovician units. Mergl (1984)

57

described a ctenostome bryozoan Marcusodictyon expectans Mergl, 1984 encrusting silicite and

58

rhyolite pebbles in the Tremadocian Třenice Formation, which is the basal unit of the basin.

59

Mergl (1984) did not observe this species on shell substrates, a result that contrasts with the

60

occurrence of M. priscum on brachiopod shells in the Lower Tremadocian of Estonia (Bassler,

61

1911). However, the validity of M. priscum as a bryozoan was questioned by Taylor (1984), who

62

interpreted it instead as a phosphatic fossil of problematic affinities. Higher in the section, in the

63

upper Tremadocian Mílina Formation, thecae of the cystoid Palaeosphaeronites crateriformis

64

(Růžička, 1927) attached to trilobites were described and figured by Mergl and Prokop (2006).

65

The larvae of these echinoderms are supposed by these authors to preferentially use exoskeletons

66

of dead or moulted trilobites in their search for available hard substrate. Holdfasts of

67

Sphenothallus sp. attached to a variety of shells, though mainly trilobites, occur in the overlying

68

Klabava Formation, especially in its upper part (upper Arenigian; Dapingian). In the Ejpovice

69

Member, situated in the uppermost part of the Klabava Formation, specimens of colonial

70

Berenicea (?) vetera encrusting pebbles (similarly to Marcusodictyon) are common. The

71

encrustations are single- or multi-layered, and together with other organisms they may form

72

stromatolitic knob-like structures attached to rocks originally occurring in a shallow-water, high-

73

energy environment near the paleo-shoreline (Mergl, 1983, 2004, 2013).

74

Turning to the Middle Ordovician, almost no epizoans have been found and described

75

from the early to middle Darriwilian Šárka Formation since the discovery of siliceous nodules in

76

Rokycany and Prague areas. The sole previous reports involve rare specimens of the epizoic

77

edrioasteroid Argodiscus rarus Plas et Prokop, 1979 and rare shells of the craniid brachiopod

78

Schizocrania multistriata, however, none of the specimens were preserved attached to any

79

surface. Very few epibionts are known from the overlying Dobrotivá Formation (upper

80

Darriwilian/lowermost Sandbian); they consist mostly of bryozoan colonies on cephalopods and

81

craniid brachiopods atached to conulariids. Horný (2009) described the tergomyan Mytoconula

82

sp. attached to shells of the probable monoplacophoran Barrandicella. Another genus of

83

monoplacophoran, Pygmaeoconus, had been known from the Šárka Formation for decades.

84

Several years earlier, Horný (2006) described a single specimen of Pygmaeoconus from the

85

Dobrotivá Formation attached to a hyolith conch, thus establishing this monoplacophoran as

86

epibiontic.

87

The number and variety of epizoic specimens increase considerably in the younger

88

formations of the Upper Ordovician in the Prague Basin. Thus, epibiontic crinoids (Budil and

89

Šarič, 1995, Prokop and Turek, 1997), edrioasteroids (Barrande, 1867, Prokop, 1965),

90

brachiopods (Havlíček, 1972, 1994, Havlíček and Vaněk, 1996, Budil and Šarič, 1995, Mergl

91

and Nolčová, 2016), bryozoans (Kácha and Šarič, 2009) and cornulitid tubeworms (Prantl, 1948)

92

have been described from the Sandbian Letná and Zahořany formations and from the Katian

93

Bohdalec Formation. These taxa occur on such shell substrates as trilobites, conulariids,

94

cephalopods, and brachiopods, the modes of life of which are discussed in the papers cited

95

above.

96

In spite of the number of papers on the epizoans from the Barrandian area this topic

97

appears to be underrated compared to other regions. In order to rectify this deficiency in our

98

knowledge of Middle Ordovician paleoecology, we here present the first systematic description

99

of multiple types of epibiont/host shell associations from the Šárka Formation. In addition to

100

discussing the taxonomy and interrelationships of the epibionts and their substrates, we consider

101

the implications of our observations for alternative interpretations of the mode(s) of life of some

102

of the substrate organisms. Importantly, all of the epibiont/host shell associations described in

103

this contribution occur as well preserved, three-dimensional molds in siliceous nodules originally

104

embedded in dark shale.

105 106 107

2. Geologic and paleontologic settings

108 109

The Barrandian area, part of which is the Prague Basin, is located in the central part of

110

the Czech Republic (Fig. 1), and has a long history of paleontological researches involving

111

numerous Lower Paleozoic localities. The area was named in honor of Joachim Barrande, the

112

highly distinguished 19th-century French collector and scientist settled in Prague and produced

113

there his classic series of monographic works. The Barrandian area forms part of the Teplá-

114

Barrandian Unit, which is composed of two tectono-stratigraphic elements, namely the

115

Cadomian basement and Early Palezoic basins; both elements underwent deformation during the

116

Variscan Orogeny (Havlíček, 1998a; Vacek and Žák, 2019). The Cadomian basement is

117

interpreted as an accretionary wedge (Hajná et al., 2011) that forms the main part of the present-

118

day denudation surface, while the Early Paleozoic basins represent minor denudation relics

119

restricted to relatively small areas. Two of the basins, the Příbram-Jince Basin (Havlíček, 1998b;

120

Fatka and Szabad, 2014) and the Skryje-Týřovice Basin (Skryje-Týřovice area sensu Havlíček,

121

1998b; Fatka et al., 2011), subsided during the Cambrian Period. Their sedimentary deposits are

122

the early to middle and middle Cambrian in age, respectively, and these are succeeded by

123

subaerial late Cambrian volcanics. The Prague Basin (Havlíček 1981, 1998c; Fig. 1) is the

124

youngest structure which formed from the Early Ordovician (Tremadocian) to the Middle

125

Devonian (Givetian). Its Ordovician succession is typified by its siliciclastic sedimentation

126

(Havlíček, 1998d), while the Silurian succession shows a gradual upward transition from

127

siliciclastic to carbonate sediments (Kříž 1992, 1998), with carbonate rocks forming the bulk of

128

the Devonian record (Chlupáč 1998, 2003). Extension of the Prague Basin over a period of one

129

hundred million years, accompanied by several episodes of volcanism, was related to the

130

spreading of the Rheic Ocean. The paleogeographic position of the Prague Basin during this

131

interval has been the subject of disagreement, though most models show it positioned on the

132

outer shelf of Gondwana (e.g., Scotese, 2001; Stampfli et al., 2002; Servais and Sintubin, 2009,

133

Žák and Sláma, 2018).

134

The Šárka Formation (Fig. 2) consists of a succession of light to dark grey to almost

135

black shale (Havlíček, 1998d). Present at certain levels within the formation are early diagenetic,

136

siliceous nodules informally called “Rokycany balls” or “Šárka balls”. Past denudation has

137

resulted in the concentration of loose nodules in the soils, from which they may easily be

138

gathered like potatoes, especially in plowed fields. The epibionts herein studied were collected in

139

this straightforward manner, and thus their exact level of occurrence within the Šárka Formation

140

is unknown. Nevertheless, most if not all specimens apparently are from the Corymbograptus

141

retroflexus Biozone (see discussion by Lajblová and Kraft, 2014). Unlike fossils preserved in

142

shale, which are compressed, those in the nodules are preserved in full relief, though typically

143

their shells are dissolved and represented by internal and external molds. Indeed, it was the

144

discovery of fossiliferous nodules that sparked initial interest of collectors in the Šárka

145

Formation. The apparent long-standing neglect of epibionts from this rock unit had two most

146

probable causes. First, many early collectors gathered only internal molds because of their

147

positive relief, which makes it easy to see the original three-dimensional form of the organisms.

148

The epibionts, by contrast, are preserved as external molds, which were less striking and thus

149

often discarded. The second reason is that epibionts often occur on partial specimens of fossil

150

taxa that are common but were and are not prized.

151

The fauna of the Šárka Formation belongs to the Placoparia-Euorthisina Association

152

(Community sensu Havlíček and Vaněk, 1990; Euorthisina Community sensu Havlíček, 1982;

153

Budil et al., 2007), which is composed predominantly of benthic elements. The most diverse and

154

abundant group are the trilobites (Havlíček and Vaněk, 1966, Havlíček, 1982) that exhibit a

155

variety of modes of life and feeding strategies (Budil et al., 2007). Brachiopods, bivalves,

156

hyolithids, gastropods, ostracods and echinoderms are also common (for a rough overview see

157

Havlíček and Vaněk, 1966), with sessile benthic species being subordinate to vagrant and

158

nektobenthic species (Havlíček, 1982; Havlíček and Vaněk, 1990). Some taxa, for example

159

bivalves (Polechová, 2013) are interpreted as infaunal. Finally, the pelagic fauna consists of

160

cephalopods, graptolites, phyllocarid crustaceans, and cyclopygids trilobites.

161 162 163

3. Material and methods

164 165

The present study is based on direct examination of several thousands siliceous nodules

166

collectively exhibiting 95 epibionts and 53 host shell specimens (Table 1; note that

167

Barrandicella is omitted because it is impossible to determine probably epizoic specimens inside

168

the deformed conulariids). Seventy-five of the epibiont specimens and 45 of the host shells were

169

collected by one of us (O. Z.) in last five years, others were donated by amateur collectors (see

170

acknowledgments section), and only few were found in old collections. All nodules were

171

gathered loose from farm fields at 9 localities (Fig. 1), which comprises almost all principal

172

localities of the Šárka Formation nodules (for more information see Lajblová and Kraft, 2014).

173

Epizoans were examined using latex casts displaying their three-dimensional shape and surface

174

topology. The figured specimens and latex casts were coated with NH4Cl to accentuate their

175

relief. The studied material is deposited in the West Bohemian Museum in Pilsen (WBM;

176

numbers with prefix S), the Museum of Dr. B. Horák in Rokycany (MBHR), and the Geological

177

Survey, Prague (CGS).

178 179 180

4. Epizoans and their hosts

181 182

4.1. Epizoan groups

183 184

In the following section we use synoptic form usual in taxonomy for the descriptions and

185

group epizoans primarily on the basis of their systematic classification. Secondarily, descriptions

186

are ordered by the host organisms.

187 188

Epizoan group: Echinodermata

189

Epizoan subgroup: Edrioasteroidea indet.

190

(Fig. 3A–C)

191 192

Material. Twelve host shells commonly with a single theca and range up to a maximum with five

193

thecae, and 24 epibiontic edrioasteroid specimens, most of which are partially disarticulated.

194 195

Host shells. Ten hyoliths and two bivalves. The hyolithid Gompholites cinctus and the

196

orthothecid Bactrotheca teres (Fig. 3A) are the most common hyoliths (four and three

197

specimens, respectively), the others belonging to the hyolithid Elegantilites euglyphus (one

198

specimen; Fig. 3B–C) or an indeterminable species (two specimens). Both bivalves belong to

199

Redonia deshayesi.

200 201

Summary of observations. The edrioasteroids occur most often as single specimens on the host

202

shell. However, some of the hyolith conchs host two specimens of different sizes. The single

203

specimen of Elegantilites bears five thecae, but this number may not be the total number because

204

it is an incomplete conch (Fig. 3B–C). The same specimen also bears a cluster of five

205

problematic objects that can be juvenile edrioasteroids or other epizoans, but cannot be identified

206

due to bad preservation.

207

The edrioasteroids on hyolith conchs seem to have no preferred position and occur

208

anywhere on its dorsal side. Specimens on the two bivalve shells (both with conjoined valves)

209

are situated in the central part of the shell. Some of the hosts are finely sculptured (Bactrotheca,

210

Elegantilites and Redonia), but Gompholites bears thickened annuli. No other distribution

211

patterns were observed.

212 213

Remarks. While there are other common species of hyolithids with low vaulted dorsal wall,

214

edrioasteroids were observed only on conchs of species having an almost circular transverse

215

cross section (Gompholites) or a rounded dorsal wall (Bactrotheca). Specimens attached to

216

Elegantilites or indetermined hyoliths also occur on the vaulted dorsal portions of these

217

substrates. Redonia is the only bivalve that was observed as an epizoan host, its valves being

218

among the most strongly vaulted in the Šárka Formation. These preferences probably point to the

219

unavailability of other surfaces that the epizoans had available for the colonization in the

220

particular environment rather then their preference of vaulted parts of shells.

221 222

Localities. On Gompholites cinctus – Osek; on Bactrotheca teres – Osek, Díly; on Elegantilites

223

euglyphus – Díly; on indeterminable hyolith – Díly, Úvaly; on Redonia deshayesi – Osek, Díly.

224 225 226

Epizoan subgroup: Edrioasteroid ?Agelacrinites bohemicus

227 228

Material. Single specimen.

229 230

Host shells. Unknown species (Solutan indent., gen. et sp. nov. sensu Lefebvre et al., 2012) of

231

solutan echinoderm.

232 233

Summary of observations. The nearly complete edrioasteroid is attached to the upper thecal

234

surface of the large solutan.

235 236

Remarks. This interaction, described and discussed in detail by Lefebvre et al. (2012), remains

237

the only observed instance of an epizoan attached to an echinoderm from the Šárka Formation.

238 239

Locality. Mýto.

240 241 242

Epizoan subgroup: Pentaradial and derived rounded to irregular indeterminate holdfasts

243

(Fig. 3D–N, 4)

244 245

Material. Seventeen specimens of host shells with a variable number of attached holdfasts. Total

246

of 41 holdfast specimens plus one fragment of cephalopod shell with more than 60 of very small

247

problematic holdfasts.

248

249

Host shells. Most of the holdfasts occur on hyoliths and mollusks, especially large

250

bellerophontids and bivalves. Among the bellerophontids, four shells of Sinuites sowerbyi host

251

one (Fig. 3G), two, four (Fig. 3J), and five (Fig. 3H) holdfasts, respectively, and one shell of

252

Sinuites cf. reticulatus exhibits two holdfasts (Fig. 3I). Among the hyoliths, two conchs of

253

Gompholites cinctus exhibit one (Fig. 3E) and three holdfasts (Fig. 3D), respectively, and one

254

specimen each of Bactrotheca teres and an indeterminable conch host a single holdfast. Three

255

specimens of Redonia deshayesi with conjoined valves, one with four (Fig. 3F) and the two

256

others with one holdfast represent a rare association of epizoans and bivalves. A single holdfast

257

attached to the gastropod specimen of Lesueurilla prima was observed (Fig. 3K), as were three

258

specimens of indetermined cephalopods, two of them bearing two and five holdfasts,

259

respectively, and the third one being densely covered by more than sixty very small, rounded

260

possible attachment bases (Fig. 3N). Lastly, the single, ramose problematic fossil exhibits seven

261

holdfasts attached to its stipes (Fig. 3L–M). It is worth noting that the overall habitus of this

262

ramose fossil resembles the monospecific gorgonacean octocoral genus Nonnegorgonides

263

Lindström, 1978 from the basal Volkhovian (lower Dapingian) and basal Kundan (lower

264

Darriwilian) of Sweden (Lindström, 1978). In addition, biometric features fit those of the

265

Nonnegorgonides ziegleri Lindström, 1978. In spite of identical shape and dimensions, and an

266

overlap of stratigraphic occurrences, a lack of the internal structure of branches restricts a

267

reliable determination.

268 269

Summary of observations. Most of the holdfasts are approximately pentaradial in shape, and only

270

a very few of those are prominently star-like with pointed roots (Fig. 4). The holdfasts are

271

usually slightly irregular, with short, rounded roots that are pentagonal to radial in shape. In their

272

center is a small pit where the stem columnal ossicles were attached. In about 50 percent of the

273

specimens (n = 10), the holdfasts occur in groups of two or more in a relatively small area,

274

sometimes even abutting and interacting with each other (Fig. 3H). The holdfasts commonly

275

differ in size, with small holdfasts occurring alongside larger specimens; most specimens are

276

0.8–1.5 mm in diameter; the largest holdfast, star-like in the shape (Figs. 3J, 4), reaches up to 5

277

mm in diameter (i.e. equal to the circumscribed circle diameter). It is worth noting that if there is

278

more than one holdfast on a shell of Sinuites, they occur exclusively in clusters and are of

279

different sizes. The same pattern was also observed on the hyolith Gompholites.

280 281

Remarks. None of the observed holdfast shows clear echinoderm features such as distinct plates

282

or bases of columnals; nevertheless, based on their pentaradial symmetry, whether obvious or

283

indistinct, the holdfasts probably belong to crinoids. Although these holdfasts are common

284

epizoans, unattached crinoid remains themselves are rare in the Šárka Formation. The majority

285

of such specimens can be assigned to Ramseyocrinus primus (Waagen et Jahn, 1899), even

286

though Jaekel (1921) described two additional species; however, Jaekel‘s type specimens are

287

probably lost, and thus the validity of his species is doubtful. There is also an eocrinoid,

288

Archaeocystites medusa Barrande, 1887, which likewise is known only from type material and

289

probably needs to be revised. The type species of genus, R. cambriensis from Lower Arenig

290

shales of Wales, has a coiled holdfast that was used as an anchor to secure the animal to muddy

291

substrates (Donovan, 1984). Attribution of holdfasts to juvenile R. primus is therefore unclear.

292 293

Localities. On Redonia deshayesi – Osek, Těškov; on Sinuites div. sp.– Osek, Díly, Mýto – pole

294

u vily, Mýto – Štěpánský rybník; on indetermined cephalopods – Osek; on Lesueurilla prima –

295

Osek; on Gompholites cinctus – Mýto – Štěpánský rybník; on Bactrotheca teres – Díly; on the

296

ramose problematic fossil – Těškov.

297 298 299

Epizoan subgroup: Rooted holdfasts

300

(Fig. 3O)

301 302

Material. One specimen.

303 304

Host shell. The bivalve Redonia deshayesi.

305 306

Summary of observations. The single, irregularly rooted holdfast is attached to a bivalve, which

307

is preserved as an incomplete external mold of a single valve on the surface of the nodule. The

308

holdfast is large relatively to the host shell, with the base of the stem measuring 1.4 mm in

309

diameter. The roots of the holdfast are 0.2–0.45 mm wide and extend across the surface of the

310

shell to a distance of 3.0 mm from the center of the stem base. The roots are straight or singly

311

branched and run out from the extended edge of the stem base.

312 313

Remarks. This holdfast belonged to a large epibiont that apparently lived for a relatively long

314

time. It is unclear whether the substrate was colonized during the life of the host or whether the

315

shell rested post-mortem on the bottom in a convex-upward orientation and stayed both exposed

316

and stable enough to support the mass of the large, tall and mature organism.

317 318

Locality. Díly.

319 320 321

Epizoan group: Unknown (? Cnidaria)

322

Epizoan subgroup: Circular holdfasts

323

(Fig. 3P–Q)

324 325

Material. Seven specimens.

326 327

Host shell. Single cephalon of Ormathops atavus.

328 329

Summary of observations. Circular holdfasts measuring 0.75–1.05 mm in diameter, most of them

330

with an inner circle measuring 0.25–0.4 mm in diameter. Each holdfast possesses a 0.05-mm-

331

wide outer rim, and the rim of the inner circle of the same width (Fig. 3Q). Two holdfasts exhibit

332

remnants of silicified rings rising up from both rims (Fig. 3P) and showing that the rims are

333

bases of the circumferential walls of the donut-like holdfasts (Fig. 3P). The holdfasts are

334

irregularly distributed on the host exoskeleton (Fig. 3Q), but four of them are situated along the

335

posterior margin of the cephalon. Two of these holdfast are attached to almost flat parts, but one

336

of them is located adaxialy on the posterior glabellar lobe (L1), and the other occurs inside the

337

circumglabellar furrow, with its is base conforming to the uneven substrate and extending

338

downward into the furrow (Fig. 3P). Two holdfasts are situated rather abaxially in the posterior

339

third of the glabella, and one holdfast is located near the anterior margin of the glabella.

340

341

Remarks. The circular holdfasts represent unique epizoans on a trilobite exoskeleton. They

342

superficially resemble attachment discs of the genus Sphenothallus; however, this taxon is very

343

rare in the Šárka Formation.

344 345

Locality. Popovice

346 347 348

Epizoan group: Monoplacophora

349

Epizoan subgroup: Pygmaeoconus porrectus

350

(Fig. 5A–J)

351 352

Material. Seventeen specimens.

353 354

Host shells. Exclusively hyoliths; except for one monoplacophoran on Elegantilites euglyphus

355

and two others on indetermined hyoliths, all of the monoplacophorans occur on Gompholites

356

cinctus.

357 358

Summary of observations. In all cases a single specimen of Pygmaeoconus is attached to the

359

hyolith. The relatively large monoplacophorans are situated in the posterior (apical) half of the

360

conch, at various distances from the apex. The epibionts occur exclusively on the vaulted dorsal

361

to latero-dorsal sides of the hyolith shells. On one specimen of Elegantilites, the Pygmaeoconus

362

specimen is abnormally attached dorso-laterally near the relatively sharp edge that divides the

363

dorsal and ventral conch surfaces. With one excepetion, all Pygmaeoconus specimens, the

364

orientation of which was possible to determine, have their anterior end facing the apex of the

365

host conch. The aperture of all epibionts is modified to conform in shape to the conch surface

366

(see also Horný, 2006). The flattened lateral walls protrude compared to anterior and posterior

367

ends. The monoplacophorans range from 1.15–6.4 mm in length, 0.75–1.6 mm in width and 1.3–

368

3.0 mm in height, reflecting different growth stages. During growth the shell underwent

369

elongation antero-dorsally, with the width increasing much more slowly to stay adapted to the

370

constant or almost constant diameter of the host conch. Therefore, the length/width ration is

371

about 1.5 in small specimens and more than three in the largest ones, indicating that the shell

372

became increasingly narrow. On the other hand, the height of the shell kept pace with shell

373

elongation, and thus, the length/height ratio is almost constant, varying between 1.5 and 1.85

374

(with just two values slightly higher than 2).

375 376

Remarks. Numerous specimens of Pygmaeoconus attached to hyolith clearly show modification

377

of the aperture as an apparent adaptation for an epibiontic mode of life, as documented

378

previously by Horný (2006). The margin of the aperture conforms to the vaulted conch, and

379

attachment often occurs in the posterior third of the conch (Fig 5E–J). The sizes of

380

Pygmaeoconus shells and their host hyoliths generally show a positive correlation, indicating

381

that the monoplacophorans attached to young hosts and subsequently grew in mutual influence.

382 383

Localities. On Gompholites cinctus – Osek, Díly, Volduchy, Těškov, Mýto – pole u vily, Mýto –

384

Štěpánský rybník; on Elegantilites euglyphus – Osek; on indeterminable hyolith – Díly, Mýto –

385

pole u vily.

386 387 388

Epizoan subgroup: indeterminable monoplacophorans

389

(Fig. 5K–L)

390 391

Material. Three specimens

392 393

Host shells. Fragments of asaphid trilobite exoskeletons (two specimens), indeterminable hyolith

394

conch (one specimen).

395 396

Summary of observations. Most of the specimens are of comparable size (1.3–1.8 mm long and

397

1.0–1.55 mm wide aperture). Of those attached to remains of large asaphid trilobites, one is

398

situated on the inner surface of the doublure (Fig. 5L), having evidently crawled into the narrow

399

space of the duplicated exoskeleton. The specimen on the hyolith is attached to its convex outer

400

surface.

401

402

Remarks. This subgroup, which can be taxonomically heterogeneous, comprises

403

monoplacophorans having a wide oval aperture. The specimens on asaphid fragments occur on

404

the flat parts of the exoskeleton (Fig. 5K–L). This is in contrast to the specimen on the hyolith

405

conch, which is attached to its vaulted part much as in the case of Pygmaeoconus. However, the

406

fragment of the host shell is too small to determine exact original location of the epibiont. Owing

407

to unfavorable preservation it is also impossible to determine whether the monoplacophoran

408

specimen is an early growth stage of Pygmaeoconus.

409 410

Localities. On asaphid fragments – Těškov, on the indeterminable hyolith – Mýto – Štěpánský

411

rybník.

412 413 414

Epizoan subgroup: Barrandicella ovata

415

(Fig. 5O–P)

416 417

Material. Three well-preserved host shells associated with several monoplacophorans and eight

418

questionable associations showing poor preservation and deformation.

419 420

Host shells. Conulariid thecae.

421 422

Summary of observations. Among approximately 150 examined conulariid specimens, twelve

423

were found with multiple, up to seven specimens of the monoplacophoran B. ovata situated

424

within the central peridermal cavity. The monoplacophorans vary in size, and within a given

425

conulariid they represent different growth stages (Fig. 5P). Five specimens of Barrandicella are

426

clearly attached to the internal wall of the conulariid because they are preserved as depressions

427

(external molds in concave relief) on internal molds of the conulariid (Fig. 5O–P). However, a

428

number of monoplacophoran specimens occur chaotically oriented within the sediment filling the

429

interior of slightly deformed thecae (Fig. 5O).

430 431

Remarks. Barrandicella ovata is unique among the observed epizoans in that it clearly prefers

432

internal over external surfaces, and occurs exclusively within empty thecae of conulariids.

433

Because the conulariids are frequently deformed owing to their apparent original flexibility (Ford

434

et al., 2016), monoplacophorans occur as epibionts only in slightly deformed thecae. Although

435

fragmentary, the conulariids may have been complete or almost complete when buried, as the

436

nodules formed around and protected only a portion of the theca (Fig. 5P). (Commonly the

437

nodule closes a part of shell while other parts remained in the surrounding shale, are flattened

438

and disappear during denudation processes when the nodule is weathered out.) Deformation may

439

also account for the random distribution of detached monoplacophoran shells within thecae.

440 441

Localities. Díly, Osek. (Questionable associations not included in the locality list.)

442 443 444

Epizoan group: Bryozoa

445

(Fig. 5M–N)

446 447

Material. A single specimen on the partly abraded surface of the nodule.

448 449

Host shell. Archaeoconularia insignis

450 451

Summary of observations. A single, large membraniporiform zoarium extending over the faces

452

and across a single corner groove (Fig. 5N) within an area measuring 34 x 17 mm. Orientation of

453

the drop-like outlines of the zooecia (preserved as U-shaped bases of the distal and lateral walls)

454

indicates that the base of the colony was situated within the corner groove (Fig. 5M). The

455

zooecia are 0.27–0.30 mm wide, and their walls are ca. 0.05 mm thick. They form a regular

456

pattern on the surface of the conulariid, being ordered in axial lines of elongated zoecia and, in

457

the same time, in diagonals formed by shifts of the zoecia in the neighboring axial lines (Fig.

458

5M). The distances of the individual zooecia in the former direction is 0.8–0.9 mm, in the latter

459

0.5–0.6 mm (measured between distalmost points of zoecia).

460 461

Remarks. This bryozoan is almost certainly cystoporate and is similar to genus Ceramopora or

462

Crepipora (A. Ernst, 2019 pers. comm.). The morphology and pattern of distribution of the

463

zoecii resemble bryozoan published as Berenicea (?) vetera (see Mergl, 2013) that is common in

464

the underlying Klabava Formation. Colonies of this bryozoan coat pebbles accumulated in

465

sedimentary iron ore beds intercalated in the rewashed tuffs in the uppermost part of the

466

Ejpovice Member. This occurrence proves that the bryozoans lived in the shallow water, and

467

suggests furthermore that the fauna of the Šárka Formation contains very few allochthonous

468

fossils from this particular environment.

469 470

Questionable specimens. In addition to the specimens described above, two fragments of

471

cephalopod shells coated with bryozoan zoaria were also found in the siliceous nodules.

472

However, it is impossible to determine whether they are from the Šárka Formation or from the

473

overlying Dobrotivá Formation, where bryozoans are more abundant. The root of the problem is

474

the fact that siliceous nodules from both units can occur in the same farm fields, and, in some

475

cases, it can be difficult to distinguish nodules from one formation from those of the other unit.

476

One specimen preserved as an internal mold represents probably a living chamber. The

477

other specimen is an external mold that may be a fragment of the phragmocone, judging by its

478

length. Both specimens are densely covered by at least ten and eight zoaria of the indeterminate

479

same species, respectively. The neighboring zoaria often touch each other their irregular edges

480

and several colonies cover a continuous area.

481 482

Localities. Specimen proven from the Šárka Formation – Osek. Two specimens of uncertain

483

stratigraphic origin – Praha-Šárka.

484 485 486

4.2. Epizoan associations

487 488

Three of the examined host shells exhibit epibionts belonging to different major taxa.

489

Thus, one specimen of Redonia with conjoined valves exhibits two pentaradial and derived

490

holdfasts on each valve alongside one or possibly two disarticulated edrioasteroids (Fig. 3F).

491

Similarly, three or more pentaradial and derived holdfasts along with Pygmaeoconus are attached

492

to an incomplete conch of Gompholites cinctus (Fig 3D). Another nodule contains three G.

493

cinctus specimens with epizoic Pygmaeoconus shells, one of which shares the host conch with an

494

edrioasteroid that appears to have overgrown the monoplacophoran. A second edrioasteroid is

495

present on the same nodule, and the total number of epizoans could have been even higher, as

496

some of the conchs are preserved only partially.

497 498 499

4.3. Summary of the host taxa

500 501

Epizoans occur on 6 % of about 200 invertebrate species in the highly diverse fauna of

502

the Šárka Formation, which contains representatives all of the principal invertebrate groups of

503

the Middle Ordovician. The most numerous host shells belong to hyoliths (60 % of studied

504

specimens), which also host the highest diversity of epibionts (four epizoan groups). This

505

observation is in accordance with the results of Galle and Parsley (2005). Bivalves and

506

bellerophontids represent the next most numerous groups of host shells, accounting, though, for a

507

much smaller share of the total number of host shells (11 % and 10 %, respectively). Together,

508

these three groups make up the vast majority (82 %) of the total number of observed host

509

specimens (Table 1). The remaining host taxa are represented by few or even single specimens.

510

It is also interesting that only three of the nine hyolith species are encrusted, and in all cases (n =

511

31) the epizoans are located on the dorsal surfaces of the conchs. No bivalves other than Redonia

512

were observed to host epizoans. With one exception (Fig. 3K), Sinuites is the only spirally coiled

513

shell (gastropods and bellerophontids) colonized by epibionts (Fig 3G–J). Barrandicella

514

associated with conulariids (Fig. 5O–P) is a special case and is not included in the foregoing

515

tally.

516

The numbers of examined host shells (third column of Table 1) are approximate but are

517

in hundreds per taxon. Other possible host shells with no epibionts (especially trilobites, bivalves

518

and gastropods) were also studied in hundreds of specimens. Thus, the frequency of occurrence

519

of epibionts in the Šárka Formation is in the order of thousandths.

520 521 522

5. Discussion

523 524

Epizoans are very rare component of the Šárka Formation compared to the abundance

525

and high diversity of fauna. Although they occur at almost every locality of siliceous nodules

526

where non-trilobite fauna is common, they have been ignored until recently. Contrary to our

527

expectations, we were not able to find almost any epizoans among thousands of possible host

528

specimens housed in the historic collections, which as noted above are tainted by strong

529

sampling bias, with external molds having been discarded in favor of internal molds. The

530

absolute majority of the studied specimens (n = 48 specimens) was collected in the last five years

531

by the present authors or by some collectors. Examination of this subset alone is free of such bias

532

and leads to the same conclusion.

533

Although some species occurring in the Šárka Formation could be autochthonous or

534

parautochthonous most of them are allochthonous. The former should be a low-oxygen tolerant

535

taxa. It is very probable that the most common trilobites such as Placoparia or Trinucleoides

536

lived in these conditions. On the other hand, epizoans occur related to the shells of taxa which

537

are supposed to live in normal conditions rather than those that are slightly dysoxic. It is inferred

538

from their abundance, typical ratio of complete and fragmented shells and their occurrence

539

individually or in monospecific clusters in contrast of prevalent presence in the different

540

accumulations and in associations with variable taxonomic composition. Therefore, the shell

541

preferences of some epizoans described above are considered to be preferentially controlled by

542

nature of the host shell/organism rather than nuances of environmental factors. Most of the host

543

shells with attached epizoans must have been transported by a relatively short distance and

544

rapidly buried in order for edrioasteroids to be preserved in a slightly disarticulated state and for

545

monoplacophorans still attached. It can be expected that the total number of epizoic organisms

546

could be higher but the edrioasteroids and monoplacophorans were objects of an easy

547

detachment during transport or decay. In contrast, it is very probable that almost all cemented

548

holdfasts survived any transport. However, the holdfasts were all that was left from the possibly

549

very fragile epizoans, as no other remains of these were found so far. It is worth noting that any

550

crinoid remains, such as calyxes, stalks, arms or even isolated columnals, are rare in the Šárka

551

Formation and are those of adult specimens. It is disproportionate to the relatively high

552

abundance of holdfast among epibionts.

553

It is usually difficult to ascertain if the described epizoans were attached to the shells of

554

living host organisms, or whether the shells were colonized post mortem. Most of the criteria for

555

distinguishing between life and post-mortem sclerobiont colonization of biotic hard substrates

556

summarized by Taylor and Wilson (2003) are not applicable in the Šárka Formation, especially

557

because of sparse and simple colonization of host specimens, virtual absence of encrusting

558

epizoans such as bryozoans and mode of preservation of shells in nodules. However there are

559

cases where attachment to a living host can be decided with a high degree of probability. For

560

example Redonia bivalve exposed free on the bottom would open its shell shortly after death

561

because of a ligament strength, yet specimens with conjoined valves were found colonized by

562

crinoid holdfasts and edrioasteroids.

563

As demonstrated by Villamil et al. (1998) for Mesozoic trigoniid bivalves and by Sumrall

564

and Zamora (2013) and Van Iten et al. (2018) for Late Ordovician conulariids, epibionts can be

565

used in certain cases to infer the mode of life of the host species, provided these organisms were

566

alive when their shell was colonized. The same may also be true for some of the host/epibiont

567

associations in the Šárka Formation. For example, Polechová (2013) argued that Redonia

568

deshayesi was infaunal, based on the presence of a myophoric buttress on the anterior adductor

569

muscle scar, which is developed in burrowers, and also because in many specimens the two

570

valves are conjoined. The articulation of four out of five Redonia specimens with epibionts

571

studied herein and the presence of holdfasts on both valves in one case suggests a semi-infaunal

572

mode of life of Redonia rather than infaunal. An attachment of epizoans on the emerged surface

573

of its shell is the most probable model for this interaction (Fig. 6A) which also implies an ability

574

of the bivalve to dig itself upwards when covered by mud. Possible modern analogues include

575

semi-infaunal, freshwater unionid mussels, the exposed posterior end of which projects above the

576

silty clay bottom sediment and is often covered by epibiontic zebra mussels (Hunter and Bailey,

577

1992).

578

Another association involving probable colonization of a living host shells is the

579

monoplacophoran Pygmaeoconus attached to hyoliths (Fig 6B), especially Gompholites (see also

580

Horný, 2006). One of the observed hyoliths is preserved with an articulated operculum and

581

helens (Fig. 5J), and five other specimens still preserve the operculum, all proving that they were

582

buried together with their epibionts in life or very shortly after death. In addition, there are other

583

indications that these epizoans used live hosts. Additionally, in all cases (n = 17) the host conch

584

exhibits only one specimen of Pygmaeoconus, always on the same side of the conch and usually

585

in the apical portion which suggests that it attached to a moderately young hyolith and stayed in

586

that primary place during its growth. Their association apparently has not restricted the

587

development of both shells – the hyolith elongated and the monoplacophoran elevated. It is a

588

question if that relationship can be considered as a mutualism and if it was limited by some

589

size/weight or size/weight proportion or, for example, by stability or shift of the center of gravity

590

of the hyolith. Anyway, it is apparent that the relationship was long-lasting (see adaptation of

591

Pygmaeoconus growth to the certain place on the conch) and allowed a survival of both animals.

592

Possibly it was very profitable for both as the monoplacophoran to be transported and to benefit

593

from the activity of the hyolith such as stirring up the substrate or feeding excrements. In return,

594

it could weigh down and anchor the light apical part of the conch (Horný, 2006) in the same time

595

causing its better stability during some activities such as digging in the substrate by hyolith and

596

better resistance to mild currents. Hydrodynamics of hyolith conch, orientation of their

597

operculum toward the current, their mode of life and possible benefits of colonization by

598

epizoans is also discussed in Marek et al. (1997) and in Galle and Parsley (2005).

599

It should be noted that there could be another reason for the typical position of

600

Pygmaeoconus in the posterior part of the hyolith conch. It is because the absolutely prevalent

601

orientation of these monoplacophorans with their anteriors facing to posteriors of hyoliths.

602

Attached to the living hyoliths that stirred up the soft detritus around their anteriors (with a

603

possibility of partly covering the apertural part of conchs or, at least temporary, semi-infaunal

604

mode of life), monoplacophorans kept outside the direct contact with clasts or dense suspension

605

by both their orientation and distance.

606

Although Pygmaeoconus shells, including those free, i.e. non-attached, are known in

607

hundreds of specimens from the siliceous nodules (meaning that it is not a rare taxon), they were

608

never found attached to a different host than hyolith conchs. It is a question whether their

609

elongate shape is not related to their host (cf. Horný, 2006), while on other hosts their opening is

610

more circular (Fig. 5K–L) and they are erroneously considered a different genus. Such

611

monoplacophorans are however much less frequent than Pygmaeoconus porrectus.

612

Edrioasteroids occurred throughout the Paleozoic and were able to attach to a variety of

613

hard substrates, including hardgrounds, pebbles, shells debris (cephalopod shells, disarticulated

614

trilobites), and also living organisms such as conulariids, trilobites, other echinoderms

615

(rhombiferans, solutans) and brachiopods (see Barrande, 1867, Prokop, 1965, Glass, 2005,

616

Sumrall et al., 2006, Sumrall and Zamora, 2011, Müller et al., 2013, Van Iten et al., 2018,

617

Sumrall and Zamora, in press). Occurrences of edrioasteroids in clusters or in association with

618

other epizoic organisms such as bryozoans and brachiopods are also quite common, and often

619

display intraspecific or interspecific spatial competitions (Sumrall et al., 2006, Sumrall and

620

Zamora, 2011, Müller et al., 2013). As mentioned by Sumrall et al. (2006) they show no

621

preference for any particular substrate or clast size. The foregoing generalizations concerning the

622

diversity of host substrates stand in contrast to our observation that edrioasteroids in the Šárka

623

Formation occur preferentially on hyoliths, especially Gompholites, and only rarely on other

624

hosts such as bivalves or solutans. It is likely that most of edrioasteroids discovered in the Šárka

625

Formation were attached to conchs and shells of living of hyoliths and bivalves (see above)

626

respectively and that their hosts represented the only stable places in otherwise muddy

627

environment with very few other suitable surfaces that would be stable and exposed long enough

628

to support growth to adult specimens. In the case of hyoliths, it is likely that they significantly

629

affected stability of the host together with holdfast bearing epizoans randomly growing on the

630

conchs in contrast to the monoplacophorans. On the other hand, together with monoplacophoran

631

Pygmaeoconus, the edrioasteroids prove that hyolith Gompholites was a favorite host taxon

632

which lived in a relation with several types of epizoans. This hyolith along with abundant but

633

less common host Bactrotheca teres were epibenthic and epifaunal or partially infaunal and

634

tolerating commensals or even profiting from symbiotic epizoans.

635

Lefebvre et al. (2012) did not interpret the timing of its attachment unequivocally for the

636

edrioasteroid ?Agelacrinites bohemicus situated on an undescribed solutan which must also have

637

grown during life of its host. The preservation of the complete, almost undisturbed host theca

638

and a relatively large edrioasteroid support a long-lasting interaction. It can be interpreted as an

639

epizoan attached to a living rather than dead host, which would be taphonomically degraded very

640

fast in any conditions exposed on the bottom.

641

Similarly, edrioasteroid thecae were composed of several hundred to several thousand

642

plates that disarticulated soon after death. Analogously with recent echinoderms, such thecal

643

plates are articulated with soft tissues that easily degrades within a few hours to days after

644

specimen death (Sumrall et al., 2006, Van Iten and Südkamp, 2010). Therefore, fossils hosting

645

articulated or slightly disarticulated edrioasteroids constitute evidence of obrution (Sumrall et al.,

646

2006, Van Iten and Südkamp, 2010, Sumrall and Zamora, 2011, Sumrall and Zamora, in press), a

647

process which likely also occurred in the depositional environment of the Šárka Formation.

648 649

The life mode of the bellerophontid Sinuites, one of the host taxa here examined, was investigated by Horný (1996). He considered it to be semi-infaunal predator having the anterior-

650

most part of its shell covered by a mantle flap, indicated by symmetric secondary shell deposits

651

on several of the fossil specimens observed by him. On most of the Sinuites specimens here

652

examined, the epibionts are located in areas outside of the presumed location of the mantle flap

653

(Fig. 3G–J) , suggesting that colonization of these gastropods took place during their life time.

654

However, shells of adult specimens are large enough to have served as a stable substrates after

655

the death of the animal, especially if the broad anterior portion of the empty shell was buried in

656

sediment.

657

Then, too, it is probable that settlement also occurred on empty shells, especially nektonic

658

cephalopods. For example, a probability that bryozoans grew on them exposed on the bottom

659

borders on certainty. However, bryozoan encrustations are rare in general in the Šárka Formation

660

and hundreds of cephalopod specimens yielded only few other epizoans. All holdfasts on

661

cephalopods were found on small, probably juvenile specimens only (Fig. 3N). Restricted

662

epizoan diversity together with extended dysoxic conditions in the Prague Basin during

663

sedimentation of the Šárka Formation and unfavorable conditions in the source area of the

664

allochthonous shells caused such a very low taphonomic feedback (sensu Kidwell and Jablonski,

665

1983).

666

It is worth noting that no conulariid was discovered to be colonized by the brachiopod

667

Schizocrania multistriata, which is also rarely occurring in in the Šárka Formation and its

668

epibiontic behavior can be expected as it is known from the overlying Dobrotivá Formation,

669

where both this species and conulariids are much more common. On the other hand, non-trilobite

670

fauna is rarer in the overlying Dobrotivá Formation and, consequently, very few epibionts are

671

known from it. Horný (2009) described specimen of tergomyan Mytoconula sp. attached to

672

Barrandicella shells. This behavior is likely to exists in the Šárka Formation as well, as small

673

tergomyans are also present, even if very rare. Bryozoan colonies are also more common in the

674

Dobrotivá Formation, especially on cephalopods.

675

Based on the detailed analysis of epibionts in the Šárka Formation and also on indicated

676

preliminary data from the Dobrotivá Formation it can be summarized that the diversity of the

677

epizoan association was very low in the Prague Basin during the Darriwilian. It increased in the

678

Sandbian as shown above. In contrast to a general features of an intensive colonization of hard

679

substrates in the Calcite Sea of the Ordovician (Taylor and Wilson 2003) a high epizoan

680

diversity is delayed in the Prague Basin and is present only in the Late Ordovician; the Early and

681

Middle Ordovician is exceptionally poor in organisms adapted to the penetration to this

682

significant niche.

683

It is necessary to keep in mind that preservation of epibionts depends on many factors

684

(see Taylor and Wilson 2003 for review and McKinney 1996 experimental taphonomy). Epibiont

685

abundance can be considered a special case of taphonomic window in general sense. As shown

686

by McKinney (1996) a loss of epibiontic organisms during transportation or fossilization

687

processes could result in its low diversity in the fossil record. However, a homogeneously

688

distributed low occurrences of the epibionts and their similar taxonomic composition in the

689

Šárka Formation along the entire Prague Basin support their primary low diversity rather than a

690

secondary taphonomic bias.

691 692 693

6. Conclusions

694 695

Rare epizoic invertebrates in the Middle Ordovician Šárka Formation in the Prague Basin

696

consist predominantly of echinoderms (edrioasteroids and indeterminable holdfast),

697

monoplacophorans (Pygmaeoconus porrectus, Monoplacophora indet. and Barrrandicella

698

ovata), and bryozoans. Observed specimens collectively occur on a variety of host shells,

699

including conulariids, trilobites, gastropods, echinoderms, cephalopods, and ramose problematic

700

fossil (tentatively determined as gorgonacean octocoral described from Baltica). However, the

701

majority of the epibionts occur on three species of hyoliths (predominantly Gompholites cinctus,

702

less often Elegantilites euglyphus and Bactrotheca teres), the bivalve Redonia, or the

703

bellerophontid Sinuites. Also, most of the epibionts colonized live hosts representing almost the

704

only stable and exposed surfaces that would support a growth of larvae to adult specimens. The

705

organisms living epibenthically on soft bottom sediments must have means to anchor themselves

706

effectively to withstand small currents and are able to extricate themselves out of deposited mud

707

together with their epizoans. Both edrioasteroids and the epizoans with holdfasts were most

708

likely epibiontic generalists and their larvae attached themselves to any suitable surface they

709

could find, often in larger numbers on the same host. On the other hand, the monoplacophoran

710

Pygmaeoconus was distinctly specialized on hyoliths, namely on the Gompholites cinctus. Thus,

711

most of hosts were living organisms who either were unable to resist them or even may have

712

benefitted from this relationship. It is considered that the former is represented by holdfast

713

bearing organisms or generalists in general, the latter by Pygmaeoconus or specialists in general

714

sense. Even if some of the epizoans found in the Šárka Formation might have colonized surface

715

of shells post mortem, only few of them were successful because the shells were either soon

716

buried even by small incremental deposition of mud, or were destabilized even by mild currents.

717

Compared to the abundance and diversity of fossil associations in the Šárka Formation

718

the epizoans are sparse. More generally, the record of epibionts in the Šárka Formation suggests

719

that occupation of this niche during the rapid increase of diversity in the initial stage of the

720

GOBE (Global Ordovician Biodiversification Event) was very low. It also indicates a delay of

721

this ecologic interactions till advanced forms of new post-Cambrian fauna appeared in the Late

722

Ordovician where epizoans are much more abundant.

723 724 725

Acknowledgments

726 727

We are grateful to Alycia L. Stigall (Ohio University, Athens, USA), Heyo Van Iten

728

(Hanover College, Indiana, USA) and anonymous reviewer for their very valuable reviews

729

significantly improving our manuscript. The two former reviewers also kindly improved English;

730

special thanks to H. Van Iten for his time spent not only by rephrasing but also restructuring the

731

text. We thank to private collector Vladislav Kozák (Prague, Czech Republic) who gave us the

732

rooted holdfast to study before he unfortunately passed away. Several specimens were donated

733

by other private collectors Štěpán Červenka (Strašice, Czech Republic) and Martin David

734

(Prague, Czech Republic). We also thank Marika Polechová (Prague, Czech Republic) and

735

Andrej Ernst (University of Hamburg, Germany) for their comments to bivalves and bryozoans,

736

respectively. This paper was financially supported by a grant from the Grant Agency of Czech

737

Republic GA18-05935S. It was also supported by Charles University, Prague, through the

738

project Progress Q45 (to P.K.) and by Ministry of Culture of the Czech Republic (DKRVO

739

2019-2023/2.IV.a, National Museum, 00023272) (to J.B.). It is a contribution to the IGCP

740

project 653.

741 742

743

References

744 745

Barrande, J., 1856. Bemerkungen über einige neue Fossilien aus der Umgebung von Rokitzan im

746

silurischen Becken von Mittel-Böhmen. Jahrbuch der Kaiserlich-königlichen geologischen

747

Reichsanstalt 2, 355, 1–6.

748

Barrande, J., 1867. Systême silurien du centre de la Bohême. 1ère Partie: Recherches

749

Paléontologiques. Vol. 3. Classe des Mollusques. Ordre des Ptéropodes. Prague, Paris (XV

750

+ 179 pp., 16 pls.).

751

Barrande, J., 1887. Systême silurien du centre de la Bohême. 1ère Partie: Recherches

752

Paléontologiques. Vol. 7. Classe des Echinodermes, Ordre des Cystidées. Leipsic, Praha

753

(XVII + 233 pp., 39 pls.).

754 755 756

Bassler, R.S., 1911. The Early Paleozoic Bryozoa of the Baltic provinces. Bulletin of the United States National Museum 77, 1–375. Budil, P., Kraft, P., Kraft, J., Fatka, O., 2007. Faunal associations of the Šárka Formation

757

(Middle Ordovician, Darriwilian, Prague Basin, Czech Republic). Acta Palaeontologica

758

Sinica 46 Suppl., 64–70.

759

Budil, P., Šarič, R., 1995. Cemented epibionts on the exoskeleton of the odontopleurid trilobite

760

Selenopeltis vultuosa tenyl Šnajdr, 1984. Věstník Českého geologického ústavu 70 (2), 29–

761

31.

762

Chlupáč, I., 1998. Devonian. In: Chlupáč, I., Havlíček, V., Kříž, J., Kukal, Z., Štorch, P. (Eds.),

763

Palaeozoic of the Barrandian (Cambrian to Devonian). Czech Geological Survey, Prague,

764

pp. 101–133.

765 766 767 768 769 770 771 772

Chlupáč, I., 2003. Comments on facies development and stratigraphy of the Devonian, Barrandian area, Czech Republic. Bulletin of Geosciences 78, 299–312. Donovan, S.K., 1984. Ramseyocrinus and Ristnacrinus from the Ordovician of Britain. Paleontology 27 (3), 623–634. Fatka, O., Micka, V., Szabad, M., Vokáč, V., Vorel, T., 2011. Nomenclature of Cambrian lithostratigraphy of the Skryje-Týřovice Basin. Bulletin of Geosciences 85 (4), 841–858. Fatka, O., Szabad, M., 2014. Biostratigraphy of Cambrian in the Příbram–Jince Basin (Barrandian area, Czech Republic). Bulletin of Geosciences 89 (2), 413–429.

773 774 775

Ford, R.C., Van Iten, H., Clark, G.R., II., 2016. Microstructure and composition of the periderm of conulariids. Journal of Paleontology 90, 389–399. Galle A., Parsley R. L., 2005. Epibiont relationships on hyolithids demonstrated by Ordovician

776

trepostomes (Bryozoa) and Devonian tabulates (Anthozoa). Bulletin of Geosciences 80 (2),

777

125–138.

778

Glass, A., 2005. Two isorophid edrioasteroids (Echinodermata) encrusting conulariids from the

779

Husrück Slate (Lower Devonian, Emsian; Rheinisches Schiefergebirge) of Germany.

780

Senckenbergiana lethaea 85 (1), 31–37. DOI 10.1007/BF03043417

781

Hajná, J., Žák, J., Kachlik, V., 2011. Structure and stratigraphy of the Teplá–Barrandian

782

Neoproterozoic, Bohemian Massif: a new plate-tectonic reinterpretation. Gondwana

783

Research 19, 495–508. DOI 10.1016/j.gr.2010.08.003

784

Havlíček, V., 1981. Development of a linear sedimentary depression exemplified by the Prague

785

basin (Ordovician–Middle Devonian; Barrandian area – central Bohemia). Sborník

786

geologických věd, Geologie 35, 7–48.

787 788 789

Havlíček, V., 1982. Ordovician in Bohemia: development of the Prague Basin and its benthic communities. Sborník geologických věd, Geologie 37, 103–136. Havlíček, V., 1998a. Variscan folding and faulting in the Lower Palaeozoic basins. In: Chlupáč,

790

I., Havlíček, V., Kříž, J., Kukal, Z., Štorch, P. (Eds.), Palaeozoic of the Barrandian

791

(Cambrian to Devonian). Czech Geological Survey, Prague, pp. 165–169.

792

Havlíček, V., 1998b. Příbram-Jince Basin. In: Chlupáč, I., Havlíček, V., Kříž, J., Kukal, Z.,

793

Štorch, P. (Eds.), Palaeozoic of the Barrandian (Cambrian to Devonian). Czech Geological

794

Survey, Prague, pp. 19–38.

795

Havlíček, V., 1998c. Prague Basin. In: Chlupáč, I., Havlíček, V., Kříž, J., Kukal, Z., Štorch, P.

796

(Eds.), Palaeozoic of the Barrandian (Cambrian to Devonian). Czech Geological Survey,

797

Prague, pp. 39–41.

798

Havlíček, V., 1998d. Ordovician. In: Chlupáč, I., Havlíček, V., Kříž, J., Kukal, Z., Štorch, P.

799

(Eds.), Palaeozoic of the Barrandian (Cambrian to Devonian). Czech Geological Survey,

800

Prague, pp. 41–79.

801 802

Havlíček, V., 1972. Life habit of some Ordovician inarticulate brachiopods. Věstník Ústředního ústavu geologického 47 (4), 229–233.

803 804 805 806 807 808 809

Havlíček, V., 1994. Kvania n. g. and Petrocrania Raymond (Brachiopoda, Ordovician) in the Prague Basin. Journal of the Czech Geological Society 39 (4), 297–302. Havlíček, V., Vaněk, J., 1966. The Biostratigraphy of the Ordovician of Bohemia. Sborník geologických věd, Paleontologie 8, 7–69. Havlíček, V., Vaněk, J., 1990. Ordovician invertebrate communities in black-shale lithofacies (Prague Basin, Czechoslovakia). Věstník Ústředního ústavu geologického 65 (4), 223–236. Havlíček, V., Vaněk, J., 1996. Dobrotivian/Berounian boundary interval in the Prague Basin

810

with a special emphasis on the deepest part of the trough (Ordovician, Czech Republic).

811

Věstník Českého geologického ústavu 71 (3), 225–243.

812

Horný, R., 1996: Secondary shell deposits and presumed mode of life in Sinuites (Mollusca,

813

Gastropoda). Acta Musei Nationalis Pragae, Series B – Historia Naturalis (Sborník

814

Národního muzea v Praze, Řada B – Přírodní vědy) 51 (1–4), 89–103.

815

Horný, R., 2006. The Middle Ordovician tergomyan mollusc Pygmaeoconus: An obligatory

816

epibiont on hyolithids. Acta Musei Nationalis Pragae, Series B – Historia Naturalis

817

(Sborník Národního muzea v Praze, Řada B – Přírodní vědy) 62 (1–2), 81–95.

818

Horný, R., 2009. Patelliconus Horný, 1961 and Mytoconula gen. n. (Mollusca, Tergomya) from

819

the Ordovician of Perunica. Acta Musei Nationalis Pragae, Series B – Historia Naturalis

820

(Sborník Národního muzea v Praze, Řada B – Přírodní vědy) 65 (1–2), 25–36.

821 822 823 824 825

Hunter, R.D., Bailey, J.F., 1992. Dreissena polymorpha (zebra mussel): Colonization of soft substrata and some effects on unionid bivalves. The Nautilus 106 (2), 60–67. Jaekel, O., 1921. Phylogenie und System der Pelmatozoen. Paläontologische Zeitschrift 3 (1), 1– 128. DOI 10.1007/BF03190413 Kácha, P., Šarič, R., 2009. Host preferences in Late Ordovician (Sandbian) epibenthic

826

bryozoans: example from the Zahořany Formation of Prague Basin. Bulletin of

827

Geosciences 84 (1), 169–178. DOI 10.3140/bull.geosci.1048

828

Kidwell, S.M., Jablonski, D., 1983. Taphonomic feedback. Ecological consequences of shell

829

accumulation. In: Tevesz, M.J.S., McCall, P.L. (Eds.), Biotic Interactions in Recent and

830

Fossil Benthic Communities. Plenum, New York, pp. 195–248.

831

Kraft, P., Štorch, P., Mitchell, C.E., 2015. Graptolites of the Králův Dvůr Formation (mid Katian

832

to earliest Hirnantian, Czech Republic). Bulletin of Geosciences 90 (1), 195–225. DOI

833

10.3140/bull.geosci.1435

834 835 836

Kříž, J., 1992. Silurian Field Excursions. Prague Basin (Barrandian), Bohemia. National Museum of Wales, Geological Series no. 13, Cardiff, 111 pp. Kříž, J., 1998. Silurian. In: Chlupáč, I., Havlíček, V., Kříž, J., Kukal, Z., Štorch, P. (Eds.),

837

Palaeozoic of the Barrandian (Cambrian to Devonian). Czech Geological Survey, Prague,

838

pp. 79–101.

839 840 841

Lajblová, K., Kraft, P., 2014. The earliest ostracods from the Ordovician of the Prague Basin, Czech Republic. Acta Geologica Polonica 64 (4), 367–392. DOI 10.2478/agp-2014-0021 Lefebvre, B., Derstler, K., Sumrall, C.D., 2012. A reinterpretation of the solutan Plasiacystis

842

mobilis (Echinodermata) from the Middle Ordovician of Bohemia. Zoosymposia 7, 287–

843

306. DOI 10.11646/zoosymposia.7.1.27

844 845 846 847 848

Lindström, M., 1978. An octocoral from the Lower Ordovician of Sweden. Geologica et Palaeontologica 12, 41–47. Marek, L., Parsley, R.L., Galle, A., 1997. Functional morphology of hyoliths based on flume studies. Věstník Českého geologického ústavu 72 (4), 351–358. McKinney, F.K., 1996. Encrusting organisms on co-occurring disarticulated valves of two

849

marine bivalves: comparison of living assemblages and skeletal residues. Paleobiology 22

850

(4), 543–567. DOI 10.1017/S0094837300016523

851

Mergl, M., 1983. Rocky-bottom fauna of Ordovician age in Bohemia (Arenigian; Prague Basin,

852

Barrandian area). Věstník Ústředního ústavu geologického 58 (6), 333–339.

853

Mergl, M., 1984. Marcusodictyon, an encrusting bryozoan from the Lower Ordovician

854

(Tremadocian) of Bohemia. Věstník Ústředního ústavu geologického 59 (3), 171–172.

855

Mergl, M., 2004. The earliest brachiopod-bryozoan dominated community in the Ordovician of

856

peri-Gondwana and its ancestors: a case study from the Klabava Formation (Arenigian) of

857

the Barrandian, Bohemia. Journal of the Czech Geological Society 49 (3–4), 127–136.

858

Mergl, M., 2013. New occurrences of the problematic fossil Berenicea (?) vetera and associated

859

stromatolic structures in the early Ordovician of the Prague Basin (Central Bohemia).

860

Zprávy o geologických výzkumech v roce 2012 46, 180–184 (in Czech, English summary).

861

Mergl, M., Prokop, J.R., 2006. Lower Ordovician cystoids (Rhombifera, Diploporita) from the

862

Prague Basin (Czech Republic). Bulletin of Geosciences 81 (1), 1–15. DOI

863

10.3140/bull.geosci.2006.01.001

864

Mergl, M., Nolčová, L., 2016. Schizocrania (Brachiopoda, Discinoidea): Taxonomy, occurence,

865

ecology and history of the earliest epizoan lingulate brachiopod. Fossil Imprint, 72 (3–4),

866

225–238. DOI 10.14446/FI.2016.223

867

Müller, P., Hahn, G., Bohatý, J., 2013. Agelacrinitid Edrioasteroidea (Echinodermata) from the

868

Middle Devonian of the Eifel (Rhenish Massif, Germany). Paläontologische Zeitschrift 87

869

(4), 455–472. DOI 10.1007/s12542-013-0170-08

870

Nolčová, L., Mergl, M., 2016. Occurrence of epibiont echinoderms in the Buchava Formation

871

(Cambrian, Drumian) at Biskoupky near Radnice (Barrandian area, Czech Republic).

872

Zprávy o geologických výzkumech 49, 43–46 (in Czech, English summary). DOI

873

10.3140/zpravy.geol.2016.24

874 875 876 877 878

Plas, V., Prokop, R.J., 1979. ?Argodiscus rarus sp. n. (Edrioasteroidea) from the Šárka Formation (Llanvirn) of Bohemia. Věstník Ústředního ústavu geologického 54 (1), 41–43. Polechová, M., 2013. Bivalves from the Middle Ordovician Šárka Formation (Prague Basin, Czech Republic). Bulletin of Geosciences 88 (2), 427–461. DOI 10.3140/bull.geosci.1426 Prantl, F., 1948. The genus Conchicolites Nicholson, 1872 (Serpulimorpha) in the Ordovician of

879

Bohemia. Věstník Královské české společnosti nauk, Třída matematicko-přírodovědecká

880

1948–9, 1–7.

881

Prokop, R., 1965. Agrodiscus hornyi gen. n. et sp. n. (Edrioasteroidea) from the middle

882

Ordovician of Bohemia and a contribution to the ecology of the edrioasteroids. Časopis

883

Národního muzea, Oddíl Přírodovědný 134 (1), 30–32.

884 885 886 887

Prokop, R.J., Turek, V., 1997. The crinoid holdfast Lichenocrinus Hall, 1866 in the Ordovician of Bohemia. Bulletin of the Czech Geological Survey 72 (3), 307–310. Růžička, R., 1927. Fauna vrstev Eulomových rudního ložiska u Holoubkova (v Ouzkém). Část II. Rozpravy České akademie věd a umění 36, 60, 1–21.

888

Scotese C.R., 2001. Atlas of earth history. Vol. 1. PALEOMAP Project, Arlington, Texas, 58 pp.

889

Servais, T., Sintubin, M., 2009. Avalonia, Armorica, Perunica: terranes, microcontinents,

890

microplates or palaeobiogeographical provinces? In: Bassett, M.G. (Ed.), Early Palaeozoic

891

Peri-Gondwana Terranes: New Insights from Tectonics and Biogeography. Geological

892

Society of London, Special Publication 325, pp. 103–115. DOI 10.1144/SP325.5

893

Stampfli, G.M., Raumer, J.F., Borel, G.D., 2002. Paleozoic Evolution of Pre-Variscan Terranes:

894

From Gondwana to the Variscan Collision. Geological Society of America Special Paper

895

364. pp. 263–280. DOI 10.1130/0-8137-2364-7.263

896

Sumrall, C.D., Sprinkle, J., Bonem, R.M., 2006. An edrioasteroid-dominated echinoderm

897

assemblage from a Lower Pennsylvanian marine conglomerate in Oklahoma. Journal of

898

Paleontology 80 (2), 229–244. DOI 10.1666/0022-

899

3360(2006)080[0229:AEEAFA]2.0.CO;2

900

Sumrall, C.D., Zamora, S., 2011. Ordovician edriosteroids from Morocco: faunal exchanges

901

across the Rheic Ocean. Journal of Systematic Palaeontology 9 (3), 425–454. DOI

902

10.1080/14772019.2010.499137

903

Sumrall, C.D., Zamora, S., in press. New Upper Ordovician edrioasteroids from Morocco. In:

904

Hunter, A.W., Álvaro, J.J., Lefebvre, B., van Roy, P., Zamora, S. (Eds.), The Great

905

Ordovician Biodiversification Event: Insight from the Tafilalt Biota, Morocco. Geological

906

Society, London, Special Publications 485. DOI 10.1144/SP485.6

907

Taylor, P.D., 1984. Marcusodictyon Bassler from the Lower Ordovician of Estonia: not the

908

earliest bryozoan but a phosphatic problematicum. Alcheringa 8 (3), 177–186. DOI

909

10.1080/03115518408618942

910

Taylor, P.D, Wilson, M.A., 2003. Palaeoecology and evolution of marine hard substrate

911

communities. Earth-Science Reviews 62 (1–2), 1–103. DOI 10.1016/S0012-

912

8252(02)00131-9

913

Vacek F, Žák, J., 2019. A lifetime of the Variscan orogenic plateau from uplift to collapse as

914

recorded by the Prague Basin, Bohemian Massif. Geological Magazine 156 (3), 485–509.

915

DOI 10.1017/S0016756817000875

916

Van Iten, H., Gutierrez-Marco, J.C., Muir, L.A., Simoes, M.G., Leme, J.M., 2018. Ordovician

917

conulariids (Scyphozoa) from the Upper Tiouririne Formation (Katian), eastern Anti-Atlas

918

Mountains, southern Morocco. In: Hunter, A.W., Álvaro, J.J., Lefebvre, B., van Roy, P.,

919

Zamora, S. (Eds.), The Great Ordovician Biodiversification Event: Insight from the Tafilalt

920

Biota, Morocco. Geological Society, London, Special Publications 485. DOI

921

10.11144/SP485.5

922

Van Iten, H., Südkamp, W.H., 2010. Exceptionally preserved conulariids and an edrioasteroid

923

from the Hunsrück Slate (Lower Devonian, SW Germany). Palaeontology, 53 (2), 403–

924

414. DOI 10.1111/j.1475-4983.2010.00942.x

925

Villamil, T., Kauffman, E.G., Leanza, H.A., 1998. Epibiont habitation patterns and their

926

implications for life habits and orientation among trigoniid bivalves. Lethaia 31 (1), 43–56.

927

DOI 10.1111/j.1502-3931.1998.tb00489.x

928 929 930

Waagen W., Jahn J. J. 1899. Classe des Echinodermes 2, Famille des Crinoides. In: Barrande, J., Systême silurien du centre de la Bohême Vol. 7. Praha (215 pp.) Žák, J., Sláma, J., 2018. How far did the Cadomian ʽterranesʼ travel from Gondwana during

931

Early Paleozoic? A critical reappraisal based on detrital zircon geochronology.

932

International Geology Review 60, 313–338. DOI 10.1080/00206814.2017.1334599

933

Zamora, S., Deline, B., Álvaro, J.J., Rahman, I.A., 2017. The Cambrian Substrate Revolution

934

and the early evolution of attachment in suspension-feeding echinoderms. Earth-Science

935

Reviews 171, 478–491. DOI 10.1016/j.earscirev.2017.06.018

936

Figure captions

937 938

Table 1. Synoptic overview on epizoans (top right in diagonally divided cells) and host

939

organisms (left bottom) in contrast to the numbers of the studied fossiliferous nodules (third

940

column). Asterisk indicates a number reduced by an uncertain number of very small holdfasts on

941

one fragment of a cephalopod shell. (Complete overview of studied specimens is available online

942

on https://www.biolib.cz/link/PaleoM2; the database is regularly updated with new finds.)

943 944

Fig. 1. A – Sketch map with the location of the denudation relic of the Prague Basin situated on

945

the territory of the central Czech Republic, between Praha and Plzeň, and the Bohemian Massif

946

(yellow shaded). B – Simplified detail of the Prague Basin with marked localities which yielded

947

the studied specimens. 1 – Osek (49°45'35"N, 13°35'20"E), 2 – Díly (49°45'25"N, 13°36'5"E), 3

948

– Volduchy (49°46'4"N, 13°37'33"E), 4 – Těškov (49°47'23"N, 13°41'43"E), 5 – Mýto – field

949

near the villa (49°47'29"N, 13°43'27"E), 6 – Mýto – Štěpánský rybník (49°47'12"N,

950

13°45'36"E), 7 – Praha-Šárka (cummulative name for several historic localities, for example

951

brickyard near 50°6'5"N 14°21'4"E), 8 – Popovice (50°10'45"N, 14°37'34"E), 9 – Úvaly

952

(50°4'26"N, 14°42'14"E); cumulative name Mýto in text refers to vaguely delimited area.

953

(Coordinates are approximate and point inside fields with nodules. For descriptions of localities

954

see Lajblová and Kraft, 2014. For interpretation of the references to color in this figure legend,

955

the reader is referred to the web version of this article.)

956 957

Fig. 2. Partial stratigraphic chart of the Ordovician in the Prague Basin (ranges of the units

958

related to the average thicknesses of the formations). The studied stratigraphic interval is shaded.

959

(Modified after Lajblová and Kraft, 2014 and Kraft et al., 2015.)

960 961

Fig. 3. Epibiontic edrioasteroids and holdfasts from the Šárka Formation. A–C – Edrioasteroidea

962

indet. A – Two thecae of different sizes attached to lateral and dorso-lateral parts of the hyolith

963

conch of Bactrotheca teres; WBM S6606. B–C – Dorsal and lateral views to the hyolith conch of

964

Elegantilites euglyphus covered along its entire length by thecae on the dorsal side (note that

965

small objects on the conch surface resemble epizoans but cannot be reliably identified); WBM

966

S6607. D–N – Pentaradial and derived echinoderm holdfasts. D–E – Holdfasts on hyolith

967

Gompholites cinctus. D – Three holdfasts of different sizes concentrated into a small area in the

968

dorso-lateral part of the conch and Pygmaeoconus porrectus in the dorsal apical part; WBM

969

S6608. E – Holdfast of imperfect pentaradial symmetry on the dorsal part of the conch; WBM

970

S6609. F – Four holdfast situated in the antero-dorsal part of the conjoined valves and

971

edrioasteroid in the dorsal portion of right valve (left down) of bivalve Redonia deshayesi; WBM

972

S6610. G–J – Holdfast on shells of bellerophontids of the genus Sinuites (G–H, J – S. sowerbyi, I

973

– S. reticulatus). G, J – Single holdfasts on lateral sides of the of the body whorls. G – Small,

974

regular holdfast; WBM S6611. J – Large, star-like holdfast; WBM S6614. H, I – Clusters of

975

holdfast on the abaxial parts of the body whorls. H – Four holdfast of various sizes and shapes;

976

WBM S6612. I – Two holdfasts of different shapes near the aperture (up); WBM S6613. K –

977

Irregular holdfast on the flat anterior surface of the body whorl of the gastropod Lesueurilla

978

prima; WBM S6615. L–M – Holdfast on ramose problematic fossil (considered to be a

979

gorgonacean octocoral Nonnegorgonides cf. ziegleri); WBM S6616. L – Overall view to the

980

whole ramose fossil. M – Detail of the main branch with several holdfast of the similar size. N –

981

Number of very small rounded holdfast irregularly distributed on the cephalopod phragmocone;

982

WBM S6617. O – Rooted holdfast with its center situated in the antero-dorsal part of the right

983

valve of bivalve Redonia deshayesi and with roots spreading radially; WBM S6618. P–Q –

984

Circular holdfasts on the cephalon of trilobite Ormathops atavus. P – Two holdfast in the

985

posterior part with their secondary mineralized walls; CGS MD 2a. Q – Counterpart of the

986

previous specimen with the irregularly distributed holdfasts; CGS MD 2b. Localities: Díly (A–C,

987

H, O), Mýto – Štěpánský rybník (D–E, I), Osek (F–G, K, N), Mýto – pole u vily (J), Těškov (L–

988

M) and Popovice (P–Q). Latex casts (A–N). Specimens coated with ammonium chloride (A–P).

989

All scale bars equal 5 mm.

990 991

Fig. 4. Idealized drawing of the shape variability of pentaradial and derived holdfasts.

992 993

Fig. 5. Epibiontic monoplacophorans and bryozoan from the Šárka Formation. A–J –

994

Pygmaeoconus porrectus on conchs of Gompholites cinctus. The set of photographs illustrates

995

the size variability of the monoplacophoran shells, their relationships to conchs of different sizes,

996

the distribution pattern from half of the conch length toward the apical end and their opposite

997

orientation related to the hyoliths with the monoplacophorans facing anteriorly to the apical end

998

of conchs. A, B – Dorso-lateral position of small specimen in the half length of concha; WBM

999

S6619. A – Oblique view. B – Lateral view. C – Dorsal view to small, relatively wide specimen

1000

on the dorsal surface in the center of concha; WBM S6620. D – Moderately sized specimen

1001

sitting on latero-dorsal surface in the center of concha, WBM S6621. E – Large specimen

1002

situated on the dorsal part in the apical part of concha; CGS CW 395e. F – Large specimen on

1003

the latero-dorsal surface in the apical part of concha; WBM S6622. G – Large specimen situated

1004

dorsally near the apex of concha; WBM S6623. H, I – Large specimen on the dorsal side of

1005

concha close to its apex; WBM S6624. H – Lateral view. I – Dorsal view. J – Two specimens of

1006

Gompholites cinctus with opercula, that with monoplacophoran latero-dorsally in apical portion

1007

has also preserved helens; WBM S6625. K–L – Indeterminable monoplacophorans related to

1008

asaphid trilobite fragments; they are sitting on the flat surfaces and have wide, almost circular

1009

aperture. K – Low cone attached to the in a relatively high space between exoskeleton and

1010

duplicature; WBM S6626. L – Small specimen hidden deeply in the very narrow space of

1011

doublured exoskeleton; WBM S6627. M–N – Bryozoan zoarium coating the conulariid theca

1012

around its corner groove; only traces of zooecia are preserved on the abraded surface; WBM

1013

S6628. M – Detail of zoarium. N – Overall view to the conulariid fragment with zoarium in its

1014

lower right part. O–P – Barrandicella ovata on the internal surfaces of conulariid thecae. O –

1015

Large specimen in apertural view, others opposite oriented inside the deformed theca; MBHR

1016

8977. P – Two specimens of different sizes in apertural view; MBHR 4096. Localities: Díly (A–

1017

D, F, H–I, O–P), Osek (E, G, M–N), Mýto – pole u vily (J) and Těškov (K–L). Latex casts (A–J).

1018

All specimens coated with ammonium chloride. All scale bars equal 5 mm.

1019 1020

Fig. 6. Reconstructed mode of life of (A) semi-infaunal bivalve Redonia deshayesi and (B)

1021

epifaunal hyolith based on the observed positions and character of epibionts, which are supposed

1022

to colonize shells during the host life; echinoderm holdfasts are shown to be attached to both

1023

shells, edrioasteroid is moreover related to the bivalve and Pygmaeoconus porrectus is sitting

1024

distinctively on the hyolith. Approximate scale bar is valid for both reconstructions.

Table 1 Epizoan

Bryozoan

Host Group

Holdfast

Taxon and approximate number of studied specimens

Conulariida

Indeterminable

> 100

Bivalvia

Redonia deshayesi

> 200

Bellerophontoidea

Sinuites div. sp.

> 500

Gastropoda

Lesueurilla prima

> 100

Cephalopoda

Indeterminable

> 200

Bactrotheca teres

> 200

Gompholites cinctus

> 500

Elegantilites euglyphus

> 100

Indeterminable

> 100

Asaphidae sp.

> 200

Ormathops sp.

> 500

Echinodermata

Soluta sp. nov.

> 10

Unknown

ramose problematic fossil

Monoplacophoran

Total

1

1

1

1 7 4

9

2 2

6

14

14

5

5 1

1 1 ?18 ?2

1 7*

7

3

3 1

1

9

10

3 4

2

4 6

4

14

5 1 1

24

14

1

20 1

6

1 2

2

2 2

2

1 1

6 6

2 2

Trilobita

2 2

7

7

1

1 1

1

1

1

7

1 Several thousands

Pygmaeoconus

Number of studied specimens (hosts\epibionts)

Hyolitha

Total

Edrioasteroid

7

1 1 1

1 49

19

25 13

17 17

3 3

95 53

Highlights Epibionts of the Bohemian Darriwilian are very poorly diversified Hyolith conch are the most often host shells Epibionts belong only to chinoderms, monolacophorans and bryozoans First discovered octocoral in the Bohemian Darriwilian bears epibionts Epibionts support reconstructions of host taxa modes of life

No conflict of interest.