- Email: [email protected]
Hepatopancreas alteration of the blue crab Callinectes sapidus by the rhizocephalan barnacle Loxothylacus texanus
Journal of Invertebrate Pathology 99 (2008) 354–356
Contents lists available at ScienceDirect
Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/yjipa
Short Communication
Hepatopancreas alteration of the blue crab Callinectes sapidus by the rhizocephalan barnacle Loxothylacus texanus José Luis Bortolini a, Fernando Alvarez b,* a b
Facultad de Ciencias, Universidad Nacional Autónoma de México, México 04510, DF, Mexico Colección Nacional de Crustáceos, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 70-153, México 04510, DF, Mexico
a r t i c l e
i n f o
Article history: Received 29 May 2008 Accepted 26 August 2008 Available online 5 September 2008 Keywords: Callinectes sapidus Loxothylacus texanus Hepatopancreas Histology
a b s t r a c t A histological study of the hepatopancreas of the blue crab Callinectes sapidus parasitized by the rhizocephalan barnacle Loxothylacus texanus was conducted to explore if the degree of development of the parasite’s rootlet system was correlated to its maturation process as seen by external characters of its reproductive body or externa. Four types of crabs were examined: control, with virgin and mature externa, and scarred. A clear progression with an increase in number and size of the parasite’s rootlets in the hosts’ hepatopancreas can be seen. Although the hepatopancreatic tubules remain functional, the hepatopancreas appears as a loose structure, completely infiltrated with L. texanus rootlets, in advanced stages of the parasitism. Ó 2008 Elsevier Inc. All rights reserved.
1. Introduction The interaction between the rhizocephalan barnacle Loxothylacus texanus and its host the blue crab, Callinectes sapidus, has been studied from many different angles in populations from within the Gulf of Mexico. The impact of L. texanus on the blue crab fishery can be considerable when spatially localized outbreaks develop (Lázaro-Chávez et al., 1996; Alvarez et al., 1998). Within the Gulf of Mexico, L. texanus is present in most of the estuaries and coastal lagoons maintaining moderate prevalence levels (1.4–17.6%) that can occasionally reach up to 53% (Alvarez and Calderón, 1996; Alvarez et al., 1998). All rhizocephalan barnacles are parasitic on other crustaceans, mainly of decapods (Høeg, 1992; Høeg and Lützen, 1995). A female larva infects the host, usually after molting by penetrating the soft exoskeleton, giving rise to an internal phase or ‘‘interna” that develops into a net of fine rootlets that will anchor and nurture the reproductive body of the parasite known as the ‘‘externa”. After a variable growing period of the interna, during a subsequent molt of the host, the externa emerges breaking the soft tegument of the internal surface of the abdomen in decapods. The externa is then fertilized by a male larva and starts growing until the gonads contained in it mature and start releasing larvae (Høeg, 1992; Høeg and Lützen, 1995). In kentrogonid rhizocephalans, the parasite mass develops in a different position relative to the site of penetration, the parasite primordium after being transported in the bloodstream attaches * Corresponding author. Fax: +52 555 55500164. E-mail address: [email protected] (F. Alvarez). 0022-2011/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2008.08.004
to the visceral mass in the abdomen (Høeg, 1992) and starts growing. The internal rootlet system in sacculinids can invade almost every host organ and tissue. Bresciani and Høeg (2001) offered a wealth of information in their review on the ultrastructure of the rhizocephalan root system. Although much is known about the topic, we present new information on the progressive invasion of the hepatopancreas of the blue crab, Callinectes sapidus, parasitized by the rhizocephalan L. texanus. The hepatopancreas was selected since it is known to be one of the main targets of the rhizocephalan rootlet system probably due to its nutrient rich condition (Shirley et al., 1985). Crabs belonging to three different phases of the infection (with virgin and mature externae, and scarred) are compared to healthy crabs using the hepatopancreas. 2. Materials and methods Blue crabs, Callinectes sapidus, were collected, using commercial baited traps, in Sontecomapan Lagoon, southern Veracruz, Mexico. Healthy adult male crabs (>10 cm of carapace width), crabs of either sex with virgin and mature externae, and scarred (>8 cm of carapace width), were selected live and fixed in Davidson’s fluid for 72 h before being transferred to 70° EtOH. To ensure that the fixative would reach all the internal organs, crabs were injected through the dorsal carapace–abdomen articulation. Within the parasitized crabs, only those with single parasites were processed. The hepatopancreas of 22 crabs was dissected (five healthy crabs, seven crabs with virgin externae, seven crabs with mature externae, and three scarred crabs) and prepared with conventional histological techniques. After being embedded in paraffin, sections 7 lm thick were stained with hematoxylin–eosin (Bell and
J.L. Bortolini, F. Alvarez / Journal of Invertebrate Pathology 99 (2008) 354–356
Lightner, 1988) and Masson´s trichromic technique (Sheehan and Hrapchak, 1980). Samples from the proximal and medial sections of the hepatopancreas were inspected and photographed using a BX Olympus compound microscope. For the SEM analysis, additional samples were postfixed in 1% OsO4, dehydrated, and critical-point dried with CO2. The samples were mounted, coated with gold, and observed using a Hitachi model S-2460N scanning electron microscope. Rootlet measurements were made using an ocular and a stage micrometers. The cellular types present in the decapod hepatopancreas used herein are those described by Gibson and Barker (1979) and Johnson (1980). The cellular morphology of the hepatopancreas changes due to various effects, such as the stage of the molt cycle, presence of food, and position within the hepatopancreas that is being observed; no ontogenetic differences between juvenile and adult organisms have been reported (Gibson and Barker, 1979; Johnson, 1980). In this study, there is probably no effect of the molt cycle in the samples coming from parasitized crabs since one of the effects of the parasitism by rhizocephalans is the arrest of the molt cycle (O’Brien and van Wyk, 1987). The sections obtained from control crabs showed tightly arranged hepatopancreatic tubules; in contrast, in premolt and postmolt blue crabs there are large fluid-filled intertubular spaces (Johnson, 1980). 3. Results In control crabs the hepatopancreatic tubules appear densely packed, the intertubular spaces are reduced with a thin layer of connective tissue in-between that may have blood vessels and fixed phagocytes (Johnson, 1980) (Fig. 1A). In this section, B and R cells appear in all tubules and the luminae are star-shaped; this is the normal condition for many decapod species (Johnson, 1980; Bell and Lightner, 1988; Factor, 1995; Cuartas and Petriella, 2002).
355
Crabs with virgin externae of L. texanus have an already heavily infiltrated hepatopancreas with the rhizocephalan rootlets, most of which are solid and with a mean diameter of 20–60 lm (Fig. 1B). At this stage of parasitization the hepatopancreatic tubules start to become separated by the numerous rootlets. The intertubular connective tissue appears still somewhat organized, B and R cell are evident in the tubules. The hepatopancreas of a crab carrying a mature externa of L. texanus shows a greater separation between hepatopancreatic tubules. Most of the parasite’s rootlets have developed a lumen and there are disperse remnants of connective tissue in the intertubular spaces (Fig. 1C). In the tubules many binucleate cells can be seen, most of which appear to be type R, being elongate and without large vacuoles; whereas some other are type B with large vacuoles close to the tubular lumen. In scarred crabs, the hepatopancreas has a more loose arrangement, the parasite’s rootlets have developed large luminae (Figs. 1D and 2B). The internal organization of the tubule, with large vacuoles, may be disrupted and the connective tissue appears completely loose. 4. Discussion The hepatopancreas due to its critical role in the digestion of food is richly supplied with hemolymph through main blood vessels that branch out into small capillaries to nourish each individual hepatopancreatic tubule. The whole organ, composed of numerous blind tubules, is ensheathed in a membrane or ‘‘tunica propria”, which covers the tubules as well, maintaining the unity of the organ and fastened to other surrounding structures (Gibson and Barker, 1979). The penetration of numerous rhizocephalan rootlets into the hepatopancreas suggests that the parasite is taking advantage of the nutrient rich medium surrounding the tubules.
Fig. 1. Light microscopy photographs of the hepatopancreas of the blue crab Callinectes sapidus in normal condition and parasitized by the rhizocephalan Loxothylacus texanus: (A) section of an unparasitized crab showing normal arrangement of tubules; (B–D) sections from C. sapidus bearing a virgin (B) and a mature externa (C), and scarred (D). C, connective tissue; Rr, rhizocephalan rootlets. (A, B, and D), stained with hematoxylin–eosin; (C) stained with Masson’s trichromic technique.
356
J.L. Bortolini, F. Alvarez / Journal of Invertebrate Pathology 99 (2008) 354–356
Fig. 2. SEM micrographs of the rootlet system of the rhizocephalan Loxothylacus texanus parasitizing the blue crab Callinectes sapidus: (A) view of a rootlet that has developed a lumen; (B) view of the growing tips of several rootlets.z
Loxothylacus texanus exerts a significant metabolic effect on the blue crab, especially when the externa is mature (Robles et al., 2002; Alvarez et al., 2002). In relation to the hepatopancreas, it can be seen the extent up to which the parasite´s rootlets can invade this organ developing more mass than the original hepatopancreatic tissue. The structural integrity of the tubules is apparently not compromised by the presence of the parasite’s rootlets, even in advanced stages of parasitization. Blue crabs with mature externae had survived in the laboratory for up to 5 months (pers. obs.), suggesting that the hepatopancreas is still functional to some degree, even when completely infiltrated with L. texanus rootlets. Finding scarred crabs may be common in certain crab–rhizocephalan associations from temperate waters where there is a marked decrease in water temperature during winter. The externa is lost during winter to avoid damage due to the changes in host behavior (Alvarez, 1993). In the case of C. sapidus from the southwestern Gulf of Mexico this is a rare condition, less than 1% of the parasitized population is scarred (Alvarez et al., 1998). The rarity of scarred blue crabs could be due to the more tropical water temperatures in which the externae can survive as long as the host survives. But since the parasite’s rootlet system seems to grow continuously, as has been shown here with the progressive invasion of the hepatopancreas, another possibility is that at some point, while still carrying a mature externa, the crab dies due to the break down of organs which cannot function properly due to the parasite’s invasion. The hepatopancreas sections from scarred crabs show that the connective tissue that holds the organ together is completely loose and very few capillaries are seen, suggesting that the functioning of the organ is seriously impaired. Bresciani and Høeg (2001) discussed that in most rhizocephalan species the rootlets have a lumen filled with fluid, but that in some other species all rootlets are solid. Although the rootlet system may have ontogenetic changes or variations depending on the location within the host, it appears that for L. texanus the rootlets increase in diameter and change form solid with a mean diameter of 25 lm, to having a well defined lumen as the parasitization progresses with diameters ranging from 30 to 45 lm (Fig. 2A). The tips of the rootlets appear to grow by projecting small apical buds that become thicker as the rootlet grow, leaving shallow constrictions (Fig. 2B). This type of rootlet is similar to that of Sacculina carcini (Bresciani and Høeg, 2001), except that no bifurcating tips were observed in L. texanus. Beyond the histological description, it would be necessary to test the levels of activity of the main enzymes present in the hepatopancreas, as well as other functions specifically, to more precisely assess in combination with the histological data how functional the organ is at the different stages of parasitism.
Acknowledgments The second author gratefully acknowledges the support received through PAPIIT-DGAPA-UNAM Grants IN208702 and IN203906-3. References Alvarez, F., 1993. The Interaction Between a Parasitic barnacle, Loxothylacus panopaei (Cirripedia, Rhizocephala), and three of its Crab Host Species (Brachyura, Xanthidae) along the east coast of North America. Ph.D. Dissertation, University of Maryland, College Park, Maryland. Alvarez, F., Calderón, J., 1996. Distribution of Loxothylacus texanus (Cirripedia: Rhizocephala) parasitizing crabs of the genus Callinectes in the southwestern Gulf of Mexico. Gulf Research Reports 9, 205–210. Alvarez, F., Alcaraz, G., Robles, R., 2002. Osmoregulatory disturbances induced by the parasitic barnacle Loxothylacus texanus (Rhizocephala) in the crab Callinectes rathbunae (Portunidae). Journal of Experimental Marine Biology and Ecology 278, 135–140. Alvarez, F., Gracia, A., Robles, R., Calderón, J., 1998. Parasitization of Callinectes rathbunae and Callinectes sapidus by the rhizocephalan barnacle Loxothylacus texanus in Alvarado Lagoon, Veracruz, Mexico. Gulf Research Reports 11, 15–21. Bell, T.A., Lightner, D.V., 1988. A Handbook of Normal Penaeid Shrimp Histology. World Aquaculture Society. pp. 114. Bresciani, J., Høeg, J.T., 2001. Comparative ultrastructure of the root system in rhizocephalan barnacles (Crustacea: Cirripedia: Rhizocephala). Journal of Morphology 249, 9–42. Cuartas, E., Petriella, A.M., 2002. Cytoarchitecture of the hepatopancreas of three species of crabs from Mar Chuiquita Lagoon, Argentina. In: Escobar-Briones, E., Alvarez, F. (Eds.), Modern Approaches to the Study of Crustacea. Kluwer Academic/Plenum Publishers, New York, pp. 39–44. Factor, J.R., 1995. The digestive system. In: Factor, J.R. (Ed.), Biology of the Lobster Homarus americanus. Academic Press Inc., pp. 395–440. Gibson, R., Barker, P.L., 1979. The decapod hepatopancreas. Oceanography and Marine Biology: An Annual Review 17, 285–346. Høeg, J.T., 1992. Rhizocephala. In: Harrison, F.W., Humes, A.G. (Eds.), Microscopic Anatomy of the Invertebrates Crustacea, vol. 9. Wiley-Liss, New York, pp. 313– 345. Høeg, J.T., Lützen, J., 1995. Life cycle and reproduction in the Cirripedia Rhizocephala. Oceanography and Marine Biology: An Annual Review 33, 427– 485. Johnson, P.T., 1980. Histology of the blue crab, Callinectes sapidus: A model for the Decapoda. New York, Praeger. 440. Lázaro-Chávez, E., Alvarez, F., Rosas, C., 1996. Records of Loxothylacus texanus (Cirripedia: Rhizocephala) parasitizing the blue crab Callinectes sapidus in Tamiahua Lagoon, Mexico. Journal of Crustacean Biology 16, 105–110. O’Brien, J., van Wyk, P., 1987. Effects of crustacean parasitic castrators (epicaridean isopods and rhizocephalan barnacles) on growth of crustacean hosts. In: Wenner, A. (Eds.), Crustacean Issues 3, Factors in Adult Growth. A.A. Balkem, Rotterdam. Robles, R., Alvarez, F., Alcaraz, G., 2002. Oxygen consumption of the crab Callinectes rathbunae parasitized by the rhizocephalan barnacle Loxothylacus texanus as a function of salinity. Marine Ecology Progress Series 235, 189–194. Sheehan, D.C., Hrapchak, B.B., 1980. Theory and Practice of Histotechnology. C.V, Mosby Company. 481 p. Shirley, S.M., Shirley, T.C., Meyers, T.R., 1985. Hemolymph studies of blue (Paralithodes platypus) and golden (Lithodes aequispina) king crab parasitized by the rhizocephalan, Briarosaccus callosus. In: Proceedings of the International King Crab Symposium Anchorage, Alaska, USA. Alaska Sea Grant Report 85-12, pp. 341–352.
Contents lists available at ScienceDirect
Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/yjipa
Short Communication
Hepatopancreas alteration of the blue crab Callinectes sapidus by the rhizocephalan barnacle Loxothylacus texanus José Luis Bortolini a, Fernando Alvarez b,* a b
Facultad de Ciencias, Universidad Nacional Autónoma de México, México 04510, DF, Mexico Colección Nacional de Crustáceos, Instituto de Biología, Universidad Nacional Autónoma de México, Apartado Postal 70-153, México 04510, DF, Mexico
a r t i c l e
i n f o
Article history: Received 29 May 2008 Accepted 26 August 2008 Available online 5 September 2008 Keywords: Callinectes sapidus Loxothylacus texanus Hepatopancreas Histology
a b s t r a c t A histological study of the hepatopancreas of the blue crab Callinectes sapidus parasitized by the rhizocephalan barnacle Loxothylacus texanus was conducted to explore if the degree of development of the parasite’s rootlet system was correlated to its maturation process as seen by external characters of its reproductive body or externa. Four types of crabs were examined: control, with virgin and mature externa, and scarred. A clear progression with an increase in number and size of the parasite’s rootlets in the hosts’ hepatopancreas can be seen. Although the hepatopancreatic tubules remain functional, the hepatopancreas appears as a loose structure, completely infiltrated with L. texanus rootlets, in advanced stages of the parasitism. Ó 2008 Elsevier Inc. All rights reserved.
1. Introduction The interaction between the rhizocephalan barnacle Loxothylacus texanus and its host the blue crab, Callinectes sapidus, has been studied from many different angles in populations from within the Gulf of Mexico. The impact of L. texanus on the blue crab fishery can be considerable when spatially localized outbreaks develop (Lázaro-Chávez et al., 1996; Alvarez et al., 1998). Within the Gulf of Mexico, L. texanus is present in most of the estuaries and coastal lagoons maintaining moderate prevalence levels (1.4–17.6%) that can occasionally reach up to 53% (Alvarez and Calderón, 1996; Alvarez et al., 1998). All rhizocephalan barnacles are parasitic on other crustaceans, mainly of decapods (Høeg, 1992; Høeg and Lützen, 1995). A female larva infects the host, usually after molting by penetrating the soft exoskeleton, giving rise to an internal phase or ‘‘interna” that develops into a net of fine rootlets that will anchor and nurture the reproductive body of the parasite known as the ‘‘externa”. After a variable growing period of the interna, during a subsequent molt of the host, the externa emerges breaking the soft tegument of the internal surface of the abdomen in decapods. The externa is then fertilized by a male larva and starts growing until the gonads contained in it mature and start releasing larvae (Høeg, 1992; Høeg and Lützen, 1995). In kentrogonid rhizocephalans, the parasite mass develops in a different position relative to the site of penetration, the parasite primordium after being transported in the bloodstream attaches * Corresponding author. Fax: +52 555 55500164. E-mail address: [email protected] (F. Alvarez). 0022-2011/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2008.08.004
to the visceral mass in the abdomen (Høeg, 1992) and starts growing. The internal rootlet system in sacculinids can invade almost every host organ and tissue. Bresciani and Høeg (2001) offered a wealth of information in their review on the ultrastructure of the rhizocephalan root system. Although much is known about the topic, we present new information on the progressive invasion of the hepatopancreas of the blue crab, Callinectes sapidus, parasitized by the rhizocephalan L. texanus. The hepatopancreas was selected since it is known to be one of the main targets of the rhizocephalan rootlet system probably due to its nutrient rich condition (Shirley et al., 1985). Crabs belonging to three different phases of the infection (with virgin and mature externae, and scarred) are compared to healthy crabs using the hepatopancreas. 2. Materials and methods Blue crabs, Callinectes sapidus, were collected, using commercial baited traps, in Sontecomapan Lagoon, southern Veracruz, Mexico. Healthy adult male crabs (>10 cm of carapace width), crabs of either sex with virgin and mature externae, and scarred (>8 cm of carapace width), were selected live and fixed in Davidson’s fluid for 72 h before being transferred to 70° EtOH. To ensure that the fixative would reach all the internal organs, crabs were injected through the dorsal carapace–abdomen articulation. Within the parasitized crabs, only those with single parasites were processed. The hepatopancreas of 22 crabs was dissected (five healthy crabs, seven crabs with virgin externae, seven crabs with mature externae, and three scarred crabs) and prepared with conventional histological techniques. After being embedded in paraffin, sections 7 lm thick were stained with hematoxylin–eosin (Bell and
J.L. Bortolini, F. Alvarez / Journal of Invertebrate Pathology 99 (2008) 354–356
Lightner, 1988) and Masson´s trichromic technique (Sheehan and Hrapchak, 1980). Samples from the proximal and medial sections of the hepatopancreas were inspected and photographed using a BX Olympus compound microscope. For the SEM analysis, additional samples were postfixed in 1% OsO4, dehydrated, and critical-point dried with CO2. The samples were mounted, coated with gold, and observed using a Hitachi model S-2460N scanning electron microscope. Rootlet measurements were made using an ocular and a stage micrometers. The cellular types present in the decapod hepatopancreas used herein are those described by Gibson and Barker (1979) and Johnson (1980). The cellular morphology of the hepatopancreas changes due to various effects, such as the stage of the molt cycle, presence of food, and position within the hepatopancreas that is being observed; no ontogenetic differences between juvenile and adult organisms have been reported (Gibson and Barker, 1979; Johnson, 1980). In this study, there is probably no effect of the molt cycle in the samples coming from parasitized crabs since one of the effects of the parasitism by rhizocephalans is the arrest of the molt cycle (O’Brien and van Wyk, 1987). The sections obtained from control crabs showed tightly arranged hepatopancreatic tubules; in contrast, in premolt and postmolt blue crabs there are large fluid-filled intertubular spaces (Johnson, 1980). 3. Results In control crabs the hepatopancreatic tubules appear densely packed, the intertubular spaces are reduced with a thin layer of connective tissue in-between that may have blood vessels and fixed phagocytes (Johnson, 1980) (Fig. 1A). In this section, B and R cells appear in all tubules and the luminae are star-shaped; this is the normal condition for many decapod species (Johnson, 1980; Bell and Lightner, 1988; Factor, 1995; Cuartas and Petriella, 2002).
355
Crabs with virgin externae of L. texanus have an already heavily infiltrated hepatopancreas with the rhizocephalan rootlets, most of which are solid and with a mean diameter of 20–60 lm (Fig. 1B). At this stage of parasitization the hepatopancreatic tubules start to become separated by the numerous rootlets. The intertubular connective tissue appears still somewhat organized, B and R cell are evident in the tubules. The hepatopancreas of a crab carrying a mature externa of L. texanus shows a greater separation between hepatopancreatic tubules. Most of the parasite’s rootlets have developed a lumen and there are disperse remnants of connective tissue in the intertubular spaces (Fig. 1C). In the tubules many binucleate cells can be seen, most of which appear to be type R, being elongate and without large vacuoles; whereas some other are type B with large vacuoles close to the tubular lumen. In scarred crabs, the hepatopancreas has a more loose arrangement, the parasite’s rootlets have developed large luminae (Figs. 1D and 2B). The internal organization of the tubule, with large vacuoles, may be disrupted and the connective tissue appears completely loose. 4. Discussion The hepatopancreas due to its critical role in the digestion of food is richly supplied with hemolymph through main blood vessels that branch out into small capillaries to nourish each individual hepatopancreatic tubule. The whole organ, composed of numerous blind tubules, is ensheathed in a membrane or ‘‘tunica propria”, which covers the tubules as well, maintaining the unity of the organ and fastened to other surrounding structures (Gibson and Barker, 1979). The penetration of numerous rhizocephalan rootlets into the hepatopancreas suggests that the parasite is taking advantage of the nutrient rich medium surrounding the tubules.
Fig. 1. Light microscopy photographs of the hepatopancreas of the blue crab Callinectes sapidus in normal condition and parasitized by the rhizocephalan Loxothylacus texanus: (A) section of an unparasitized crab showing normal arrangement of tubules; (B–D) sections from C. sapidus bearing a virgin (B) and a mature externa (C), and scarred (D). C, connective tissue; Rr, rhizocephalan rootlets. (A, B, and D), stained with hematoxylin–eosin; (C) stained with Masson’s trichromic technique.
356
J.L. Bortolini, F. Alvarez / Journal of Invertebrate Pathology 99 (2008) 354–356
Fig. 2. SEM micrographs of the rootlet system of the rhizocephalan Loxothylacus texanus parasitizing the blue crab Callinectes sapidus: (A) view of a rootlet that has developed a lumen; (B) view of the growing tips of several rootlets.z
Loxothylacus texanus exerts a significant metabolic effect on the blue crab, especially when the externa is mature (Robles et al., 2002; Alvarez et al., 2002). In relation to the hepatopancreas, it can be seen the extent up to which the parasite´s rootlets can invade this organ developing more mass than the original hepatopancreatic tissue. The structural integrity of the tubules is apparently not compromised by the presence of the parasite’s rootlets, even in advanced stages of parasitization. Blue crabs with mature externae had survived in the laboratory for up to 5 months (pers. obs.), suggesting that the hepatopancreas is still functional to some degree, even when completely infiltrated with L. texanus rootlets. Finding scarred crabs may be common in certain crab–rhizocephalan associations from temperate waters where there is a marked decrease in water temperature during winter. The externa is lost during winter to avoid damage due to the changes in host behavior (Alvarez, 1993). In the case of C. sapidus from the southwestern Gulf of Mexico this is a rare condition, less than 1% of the parasitized population is scarred (Alvarez et al., 1998). The rarity of scarred blue crabs could be due to the more tropical water temperatures in which the externae can survive as long as the host survives. But since the parasite’s rootlet system seems to grow continuously, as has been shown here with the progressive invasion of the hepatopancreas, another possibility is that at some point, while still carrying a mature externa, the crab dies due to the break down of organs which cannot function properly due to the parasite’s invasion. The hepatopancreas sections from scarred crabs show that the connective tissue that holds the organ together is completely loose and very few capillaries are seen, suggesting that the functioning of the organ is seriously impaired. Bresciani and Høeg (2001) discussed that in most rhizocephalan species the rootlets have a lumen filled with fluid, but that in some other species all rootlets are solid. Although the rootlet system may have ontogenetic changes or variations depending on the location within the host, it appears that for L. texanus the rootlets increase in diameter and change form solid with a mean diameter of 25 lm, to having a well defined lumen as the parasitization progresses with diameters ranging from 30 to 45 lm (Fig. 2A). The tips of the rootlets appear to grow by projecting small apical buds that become thicker as the rootlet grow, leaving shallow constrictions (Fig. 2B). This type of rootlet is similar to that of Sacculina carcini (Bresciani and Høeg, 2001), except that no bifurcating tips were observed in L. texanus. Beyond the histological description, it would be necessary to test the levels of activity of the main enzymes present in the hepatopancreas, as well as other functions specifically, to more precisely assess in combination with the histological data how functional the organ is at the different stages of parasitism.
Acknowledgments The second author gratefully acknowledges the support received through PAPIIT-DGAPA-UNAM Grants IN208702 and IN203906-3. References Alvarez, F., 1993. The Interaction Between a Parasitic barnacle, Loxothylacus panopaei (Cirripedia, Rhizocephala), and three of its Crab Host Species (Brachyura, Xanthidae) along the east coast of North America. Ph.D. Dissertation, University of Maryland, College Park, Maryland. Alvarez, F., Calderón, J., 1996. Distribution of Loxothylacus texanus (Cirripedia: Rhizocephala) parasitizing crabs of the genus Callinectes in the southwestern Gulf of Mexico. Gulf Research Reports 9, 205–210. Alvarez, F., Alcaraz, G., Robles, R., 2002. Osmoregulatory disturbances induced by the parasitic barnacle Loxothylacus texanus (Rhizocephala) in the crab Callinectes rathbunae (Portunidae). Journal of Experimental Marine Biology and Ecology 278, 135–140. Alvarez, F., Gracia, A., Robles, R., Calderón, J., 1998. Parasitization of Callinectes rathbunae and Callinectes sapidus by the rhizocephalan barnacle Loxothylacus texanus in Alvarado Lagoon, Veracruz, Mexico. Gulf Research Reports 11, 15–21. Bell, T.A., Lightner, D.V., 1988. A Handbook of Normal Penaeid Shrimp Histology. World Aquaculture Society. pp. 114. Bresciani, J., Høeg, J.T., 2001. Comparative ultrastructure of the root system in rhizocephalan barnacles (Crustacea: Cirripedia: Rhizocephala). Journal of Morphology 249, 9–42. Cuartas, E., Petriella, A.M., 2002. Cytoarchitecture of the hepatopancreas of three species of crabs from Mar Chuiquita Lagoon, Argentina. In: Escobar-Briones, E., Alvarez, F. (Eds.), Modern Approaches to the Study of Crustacea. Kluwer Academic/Plenum Publishers, New York, pp. 39–44. Factor, J.R., 1995. The digestive system. In: Factor, J.R. (Ed.), Biology of the Lobster Homarus americanus. Academic Press Inc., pp. 395–440. Gibson, R., Barker, P.L., 1979. The decapod hepatopancreas. Oceanography and Marine Biology: An Annual Review 17, 285–346. Høeg, J.T., 1992. Rhizocephala. In: Harrison, F.W., Humes, A.G. (Eds.), Microscopic Anatomy of the Invertebrates Crustacea, vol. 9. Wiley-Liss, New York, pp. 313– 345. Høeg, J.T., Lützen, J., 1995. Life cycle and reproduction in the Cirripedia Rhizocephala. Oceanography and Marine Biology: An Annual Review 33, 427– 485. Johnson, P.T., 1980. Histology of the blue crab, Callinectes sapidus: A model for the Decapoda. New York, Praeger. 440. Lázaro-Chávez, E., Alvarez, F., Rosas, C., 1996. Records of Loxothylacus texanus (Cirripedia: Rhizocephala) parasitizing the blue crab Callinectes sapidus in Tamiahua Lagoon, Mexico. Journal of Crustacean Biology 16, 105–110. O’Brien, J., van Wyk, P., 1987. Effects of crustacean parasitic castrators (epicaridean isopods and rhizocephalan barnacles) on growth of crustacean hosts. In: Wenner, A. (Eds.), Crustacean Issues 3, Factors in Adult Growth. A.A. Balkem, Rotterdam. Robles, R., Alvarez, F., Alcaraz, G., 2002. Oxygen consumption of the crab Callinectes rathbunae parasitized by the rhizocephalan barnacle Loxothylacus texanus as a function of salinity. Marine Ecology Progress Series 235, 189–194. Sheehan, D.C., Hrapchak, B.B., 1980. Theory and Practice of Histotechnology. C.V, Mosby Company. 481 p. Shirley, S.M., Shirley, T.C., Meyers, T.R., 1985. Hemolymph studies of blue (Paralithodes platypus) and golden (Lithodes aequispina) king crab parasitized by the rhizocephalan, Briarosaccus callosus. In: Proceedings of the International King Crab Symposium Anchorage, Alaska, USA. Alaska Sea Grant Report 85-12, pp. 341–352.