5© SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



Since most isopods have biting and chewing mouth parts, the con- 

 version of the mouth parts in the embryo of Paragnathia into piercing 

 organs may be regarded as an embryonic metamorphosis preparing the 

 future larva for its prospective Hfe as a parasite. 



Danalia ciirvata Fraisse. — This isopod belongs to the suborder 

 Epicaridea, the members of which are parasitic on other crustaceans. 

 It gives us an example of the sex versatility of some of the epicaride- 

 ans in which the animal is first a functional male and then a functional 

 female. In its female role Danalia curvata attaches itself to a crab 

 infested with a rhizocephalan and feeds either on this parasite in its 

 external state or on its roots in the host. Here the female is in- 

 seminated by a young free-swimming male, after which the male 

 attaches to the crab and becomes a female. In this manner, though 

 the species is hermaphroditic, it avoids self-fertilization. The follow- 

 ing outline of the life history of Danalia curvata is taken from the 

 work of G. Smith (1906) and of Caullery (1908). 



The mature female (fig. 19 H) has no likeness whatever to a 

 crustacean; she is little more than a sac full of eggs attached to the 

 crab by a narrow stalk inserted into the crab's body. The young on 

 hatching leave the brood pouch of the mother and become free-swim- 

 ming larvae. At this stage the larva (A) is recognizable as an im- 

 mature isopod, and is called a microniscus. The larva is distinctly 

 segmented, has two pairs of antennae, five pairs of thoracic append- 

 ages, and five pairs of pleopods, but eyes are absent and the mouth 

 parts are reduced to a pair of sty li form mandibles enclosed in a small 

 buccal cone. The microniscus larva may adopt a copepod as a tempo- 

 rary host, as do most of its relatives. After several moults it takes 

 on a different form (B, C) and is now termed a cryptoniscus, pre- 

 sumably because its isopod characters are less evident. The body is 

 more elongate and eyes have been developed, the appendages are 

 retained ; the cryptoniscus is a free-swimming stage. Within its body 

 is a pair of large hermaphroditic sex organs (B), each of which con- 

 tains in its anterior end a small ovary {Ov) and in its posterior part 

 a large testis {Tes). The testes rapidly develop and become filled with 

 an abundance of spermatozoa. The larva is now a functional male. 



The male cryptoniscus seeks out a crab parasitized by a sexually 

 mature female of his own species (G). After accomplishing the 

 insemination of the female the larv^al male attaches himself to the 

 crab or to the Sacculina on the crab by the first two pairs of his 

 chelate pereiopods. Then a moult takes place, the cuticle being shed 

 in two pieces from the opposite ends of the body, and it is then seen 

 that the larva has undergone a radical change of structure within the 



