ENTONISCIDAE, Kossmann, 1881

McDermott, John J., 2011, Parasites of shore crabs in the genus Hemigrapsus (Decapoda: Brachyura: Varunidae) and their status in crabs geographically displaced: a review, Journal of Natural History 45 (39 - 40), pp. 2419-2441 : 2430-2431

Family ENTONISCIDAE

Entoniscid isopods live in the haemocoele of brachyuran and anomuran crabs, and one species infects an alpheid shrimp. Females have evolved a morphology making them hardly recognizable as isopods and almost completely adapted for reproductive purposes ( Lester 2005). They are enclosed within a membranous sheath produced by the host, and external contact is made via a pore located in the wall of the gill chamber or other parts of the host body. Males are minute and maintain the more typical isopod characteristics. Free-swimming epicaridium larvae are released via the external pore, attach to copepod intermediate hosts and eventually metamorphose into larval stages that infect the definitive crustacean host. Parasitic castration and changes in host secondary sexual characteristics may result from infection. Portunion conformis parasitizes H. nudus and H. oregonensis along the Pacific coast of North America ( Muscatine 1956; Kuris et al. 1980; Shields and Kuris 1985). Prevalence of the isopod in H. oregonensis in collections from Mexico to Vancouver Island, Canada ranged from ∼ 20 to 86%, with a mean of ∼ 35% ( Kuris et al. 1980). Parasitism was generally less frequent in H. nudus , and ranged from ∼ 2 to 67%, with a mean of ∼ 17%. The latter species has a more compressed geographical range than H. oregonensis , but is sympatric over part of its distribution. A detailed study of the host–parasite relationship of Portunion conformis by Kuris et al. (1980) documents castration, particularly in female crabs, and feminization of male secondary sex characters, as well as parasite mortality induced by infected hosts. A thickened host-produced sheath encloses dead parasites. Castrated female crabs may redevelop gonads and reproduce in cases following death of the female parasite. Malformation (swelling) of the host’s branchial carapace was noted in H. nudus by Shields and Kuris (1985) but not to the extent found in bopyrid isopod infestations of the branchial chambers in other brachyurans, anomurans and caridean shrimp ( Baer 1951; Kensley and Schotte 1989; McDermott 1991b). Bopyrid isopods have never been reported from either of these two eastern Pacific crabs (n at least 10,000 examined by Shields and Kuris (1985)).

Poulin et al. (2003), while studying other parasites of H. crenulatus in New Zealand, found four crabs infected with an undescribed species of entoniscid thought to be Portunion (Poulin, personal communication). The host–parasite relationship between Portunion sp. and H. crenulatus from New Zealand (and probably the same species seen by Poulin et al. 2003) was studied by Brockerhoff (2004). This parasite had a prevalence of 19.0% (n = 2300) in H. crenulatus , was absent from 636 specimens of H. sexdentatus , but was present in the grapsids Cyclograpsus lavauxi H. Milne Edwards, 1853 (34.1%, n = 1650) and Austrohelice crassa Dana, 1851 (11.6%, n = 825), and the ocypodid crab Macrophthalmus hirtipes . Usually there was one female isopod per crab, but up to seven occurred. Males ranged from one to three per female. Castration occurred in female hosts.

Koehler and Poulin (2010) identified Portunion sp. in one specimen of H. crenulatus (1 of 51; 2.0%). Fifty specimens of H. sexdentatus were uninfected. One of each of the following crabs was infected with this entoniscid: Austrohelice crassa , Cyclograpsus lavauxi and Macrophthalmus hirtipes .

Kuris et al. (1979) described two kinds of virus particles in tissues of Portunion conformis and its host H. oregonensis collected in San Francisco Bay, California. No pathology or mortality was apparent in either parasite or host.