ASSOCIATIONS 599 



dilation of the posterior thoracic segments. When development is complete 

 the larvae fall off and metamorphose into adults, which no longer feed. 

 After fertilization the embryos develop within the body of the female (67). 



The cymothoids are mostly external parasites offish. The Epicaridea are 

 highly modified parasites found on other Crustacea, and they recall the 

 parasitic cirripedes in the extent of their transformations. The adults show 

 considerable diversity in structure and habits but the larval forms are 

 similar to one another and pass through three successive stages known as 

 the epicaridium, microniscus and the cryptoniscus forms. The eggs are 

 incubated in a special chamber situated either beneath the thorax or 

 internally, and the eggs on hatching give rise to the epicaridium form, which 

 has typical isopod features. This swims actively in the plankton until it 

 encounters a copepod such as Calanus or Acartia to which it adheres by 

 its thoracic appendages, and feeds by sucking in the haemolymph of its 

 host. After a moult the parasite passes into the microniscus stage, and when 

 about to quit its copepod host it undergoes a further transformation into 

 a cryptoniscus larva which becomes free-swimming once more. The crypto- 

 niscus larva is elongated, still with normal appendages, but possesses 

 piercing mouth parts which it uses to attack its definitive host (Fig. 14.11). 



Among the Epicaridea the bopyrid parasites are probably the best 

 known. These animals are parasitic on prawns, anomurans and brach- 

 yurans. In Bopyrus fougerouxi, parasitic on the common prawn Palaemon 

 serratus, the female is large, distinctly segmented and provided with 

 appendages. A definite asymmetry is apparent and corresponds to the 

 lateral position assumed by the parasite on the host. The prawn is attacked 

 when still quite small, host and parasite grow in parallel and even moult 

 together. Nourishment is obtained by sucking in the host's blood and 

 storing it in the greatly enlarged hepatic diverticula. Bopyrus is dioecious 

 and the female is accompanied by a dwarf male which adheres to its under- 

 surface. 



The cryptoniscid Liriopsis pygmaea is a highly modified epicaridian liv- 

 ing as a hyperparasite on Peltogaster, itself a rhizocephalan parasite of the 

 hermit crab Eupagurus. During its growing phase Liriopsis feeds on the 

 body fluids of Peltogaster, and causes atrophy of the ovary in its host. 

 Once mature, however, it ceases to feed, and the ovary of Peltogaster 

 regenerates and becomes functional. This is an interesting instance of 

 partial and temporary castration which may be compared with more pro- 

 found changes induced by bopyrid and rhizocephalan parasites (3, 94). 



The entoniscids inhabiting the visceral cavity of porcellanid and 

 brachyuran crabs are the most specialized of epicaridian parasites. The 

 cryptoniscus larva of Portunion maenadis, to mention one species, pene- 

 trates the hypodermis of the shore crab Carcinus maenas, where it moults 

 and metamorphoses into a larval form devoid of appendages (Fig. 14.11). 

 It gradually makes its way into the visceral cavity and, in the case of the 

 female, becomes a saccular structure surrounded by a cellular sheath and 

 devoid of all resemblance to an isopod. Segments and appendages are no 



