PARASITIC CRUSTACEA 119 



The body become longer and the larva is now called a cryptoniscus. 

 This leaves the copepod and seeks out the final host. 



In one family of the Epicaridea, the Bopyridae. the cryptoniscus 

 makes its way into the gill chamber of a young decapod. The larva 

 moults and loses the pleopods from its abdomen; it then grows in a 

 series of moults, which coincide with those of its host. The parasite 

 feeds by sucking blood, and this tempts one to think that the 

 moults of the parasite may be influenced by the hormones circulat- 

 ing in the host. 



The first cryptoniscus to take up residence in a gill chamber 

 invariably develops into a female, and any later arrivals develop 

 into males. As a rule only one adult male is found with a female. 

 If a young female is removed from its host and placed in a gill 

 chamber with a mature female, the development of the young one 

 is retarded and it eventually becomes a male. Young males will 

 develop into females if they are removed from the presence of a 

 female and placed in a gill chamber of an uninfected crab. 



The later development of the two sexes is rather different. The 

 males remain small and resemble the cryptoniscus. The females 

 grow considerably and sometimes lose some of their legs. The brood 

 pouch develops on the underside and is often relatively enormous, 

 capable of holding large numbers of eggs until they hatch as 

 epicaridian larvae to start the whole cycle again. 



Although the bopyrids are external parasites the draining of 

 blood from the host has serious internal effects. In general these are 

 similar to the effects of Sacculina on crabs. The reproductive organs 

 of the host are reduced, and parasitised males become feminised. 

 These effects are so marked that some of the early biologists thought 

 that onlv female hosts were infected. 



The Liriopsidae, which form another family of the Epicaridea. 

 are parasites on the Rhizocephala; they are parasites of parasites. 

 Danalia is a parasite on Sacculina, and Liriopsis parasitises Pelto- 

 gaster, which is itself a parasite on hermit crabs. It is interesting 

 that Liriobsis has a similar effect on Peltogaster to the effect 

 which Peltogaster has on its host. The ovaries of an infected Pelto- 

 gaster are usually degenerate and poorly developed. However, the 

 isopod does not live as long as its cirripede host and it eventually 

 drops off. The ovary of Peltogaster then regenerates, and eggs are 

 produced. 



Distortion of the grossest kind is found in members of the family 

 Entoniscidae (fig. 52). These are internal parasites of crabs. In life 



