host has spawned. This and other nemerteans 

 have been described from a number of crabs, 

 inchidinjr the green crab, of Europe (Coe, 1902; 

 Humes, 1942). 



A localized mortality of blue crabs, thought 

 to be caused by parasitization by leeches, Mij- 

 zobdcUa Inr/iibris Leidy, was reported from a 

 Florida river by Hutton and Sogandares-Ber- 

 iial (1959). A sample of 7 crabs had 32 leeches 

 iittached near the base of the legs and near 

 perforations in the exoskeleton. The parasite is 

 known from the Atlantic and Gulf coasts of the 

 United States but had not previously been con- 

 sidered to cause mortalities (Moore, 1946). 



Other leeches occur on crabs. Oka (1927) de- 

 scribed Carcinohdella kaiiibir from Japanese 

 edible crabs, Chioiioecetes opilio. Egg cases and 

 adults of the leech NotostoinobdcUa ciidostoma 

 (Johansson) are common on Alaska king crabs, 

 particularly during summer (Moore and Meyer, 

 1951; Bright et al., .see footnote 3). Unde- 

 scribed worms, probably leeches, were seen by 

 MacKay (1942) on the abdomens of female 

 Dungtness crabs, Cancer magisti r Dana, from 

 British Columbia. The worms were much larger 

 on egg-bearing crabs and were found chiefly 

 among the eggs. 



Disei?ses (.uused h\ Parasitic (Tustaceans 



Parasitic crustaceans — rhizocephalans, iso- 

 pods, and copepods — also infest crabs. 



Many species of crabs, in many parts of the 

 world, are parasitized by rhizocephalan Cirri- 

 pedia. These parasites invade the host's body 

 and cause degeneration of the gonads (Rein- 

 hard, 1956). The tumorlike body of the rhizo- 

 cephalan ramifies throughout much of the crab 

 and causes extensive morphological changes. 

 The crab is usually sterilized, secondary sex 

 characters are modified, and molting is often 

 inhibited (Giard, 1888; Potts, 1906; Smith, 

 1906; Cantacuzene, 1925; Reinhard, 1950; Ichi- 

 kawa and Yanagunachi, 1957). 



Brachyuran or true crabs are parasitized by 

 members of the rhizocephalan family Sacculini- 

 dae. In U.S. waters, crabs most frequently para- 

 sitized are the green crab of the Atlantic coa.st, 

 and the masking crab, Loxorhy}ichus grandis, 

 the kelp crab, Pugettia producta (Randall), 

 and the black-clawed crab, Lophopanoepeus bel- 

 his (Stimpson) of the Pacific coast. Green crabs 



and swimming crabs, Macropipus (Portumis) 

 holsatus (Fabricius), from the English coast 

 are parasitized by Sacciilina carciiii Thompson 

 (Delage, 1884; Day, 1935; Foxon, 1940). Blue 

 crabs from the Gulf of Mexico are parasitized 

 by the rhizocephalan Loxothylacus texauus 

 (Hopkins, 1957a). Mud crabs, Eiirijpanopetis 

 depressHS (Smith), from lower Chesapeake Bay 

 (Virginia) were discovered by Van Engel, Dil- 

 lon, Zwerner, and Eldridge (1966) to have high 

 incidences of the sacculinid Loxnthijlaciis pano- 

 paei (Gissler). The localized nature of the in- 

 festations suggested that the parasite had been 

 introduced with its hosts in shipments of oys- 

 ters from the Gulf of Mexico. 



Many species of anomuran crabs may be par- 

 asitized by rhizocephalans. King crabs, Para- 

 litlwdes platypus, from Alaskan waters are oc- 

 casionally invaded, probably by ,i species of 

 Peltogaster (J. B. Kirkwood, written commu- 

 nication, April 14, 1967). Hermit crabs are also 

 frequently invaded by members of the family 

 Peltogastridae. Reinhard (1942), who exam- 

 ined 3,092 Pagurus pubescens Kroyer from the 

 Maine coast of the United States, found 13.7 

 percent parasitized by Peltogaster pagini 

 Rathke. The same rhizocephalan occurs on the 

 coast of France, where its host is Pagurus 

 bernhardus (L.) (Perez, 1927, 1928, 1931a, 

 1931b, 1931c). Infestation can have significant 

 effects on crab populations, since parasitization 

 usually c.iuses degeneration of host gonads. 

 Perez (1929, 1931a), however, found interest- 

 ing evidence for sterilization and mortalities of 

 Peltogaster paguri because of hyperparasitiza- 

 tion by the epicaridean isopod Li) iopsis pi/g- 

 maea (Rathke) ; in some samples from north- 

 ern France, most of the rhizocephalans were 

 parasitized. Perez believed that this parasitiza- 

 tion was an important control for Peltogaster 

 populations. 



Epicaridean isopods can also be significant 

 parasites of crabs. Two families are of impor- 

 tance: the Bopyridae, which live principally in 

 the gill chambers, and the Entoniscid;ie, which 

 invade the haemocoele. In some species mor- 

 phological modification for parasitic existence 

 parallels that in rhizocephalans (Veillet, 1945). 

 Effects on the crab host often include steriliza- 

 tion and changes in secondary sexual charac- 

 teristics (Tucker, 1930; Reverberi, 1943, 1952: 



DISEASES OF THE MARINE BIVALVE MOLLUSCA AND CRUSTACEA 



355 



