ASSOCIATIONS 605 



Synagogidae, which are external parasites of antipatharians and crinoids; 

 the Petrarcidae, which live in the body cavities of abyssal madreporarian 

 corals; and the Dendrogasteridae, which are endoparasites of madreporar- 

 ian corals, echinoids and asteroids. Development in ascothoracids usually 

 involves nauplius, metanauplius and cypris larvae. The nauplius, when 

 present, lacks the anterolateral horns characteristic of cirripedes, and the 

 cypris is provided with piercing and sucking mouth parts. The mantle 

 sometimes becomes greatly enlarged in the adult female, and the eggs are 

 retained for some time and commence their development in the mantle 

 cavity. 



Synagoga (Synagogidae) is a small ectoparasite found on the stems of the 

 crinoid Metacrinus. It is provided with a bivalved carapace, buccal mouth 

 parts organized for piercing the host's tissues, and possesses typical crusta- 

 cean features recalling those of a cypris larva. In this form the sexes are 

 separate and the males may be dwarf in size. Myriocladus (Dendrogaster- 

 idae), an endoparasite of Aster ias, is much more specialized in organization. 

 The bulk of the body in the female is made up of ramified digestive diverti- 

 cula covered by a mantle layer, and it feeds by absorbing nourishment from 

 the body fluids of its host. The dwarf males, on the other hand, retain the 

 appendages and have a cypris-like organization (71). 



Copepods. Parasitism is very extensive among copepods, which display 

 all gradations from forms in which there is a slight reduction of append- 

 ages to highly modified species in which the body is reduced to a saccular 

 mass. They infect a remarkably wide variety of marine animals, including 

 alcyonarians, actinians, polychaetes, Crustacea, molluscs, echinoderms, 

 ascidians, fish and cetaceans (Fig. 14.16). Moreover, they have adapted 

 themselves to most diverse modes of existence, and may be encountered 

 outside the host, or internally in the alimentary canal, blood vessels and 

 coelomic cavity. Sexual dimorphism is usually well marked, and the male 

 is either free-living or minute in size and dependent upon the female. 

 Nutrition is derived by sucking in fluids of the host. 



Copepods of the family Caligidae are common parasites of fish and are 

 known as fish-lice. Species of Monstrillidae resemble gnathiids in that the 

 young stages are parasitic, while the adults lead an independent existence. 

 These remarkable animals are internal parasites of polychaetes and are 

 highly modified for their manner of life. In Cymbasoma rigidum, for ex- 

 ample, the eggs hatch into free-swimming nauplii, which appear normal 

 save for the absence of a gut. The nauplius finally invades a serpulid 

 worm. Salmacina, in which it moults and becomes reduced to a cellular 

 mass (Fig. 14.17). Then, by amoeboid movement, it migrates into a longi- 

 tudinal blood vessel of its host and there assumes an elongate cylindrical 

 form, with two long anterior appendages which are employed in absorbing 

 nutriment from the host. The parasite is invested by a cuticle, in which a 

 gradual transformation into the adult form takes place. This has a definite 

 copepod appearance, although the gut has atrophied and buccal and 

 thoracic appendages are wanting. After escaping from the host poly- 



