The Epicarida include an immense number of Isopods, parasitic upon other Crustacea. In the adult state they become greatly deformed, and offer very few characters of classificatory value, but they all pass through certain highly characteristic larval stages which are essentially similar in the different families. All the species are protandric hermaphrodites, each individual being male while in a larval state, and then losing its male organisation and becoming female as the parasitic habit is assumed. Two series of families are recognised according to the larval stages passed through, the =Cryptoniscina=, in which the adult male organisation is assumed in the Cryptoniscus stage, and the female condition is imposed directly upon this form, and the =Bopyrina=, in which the Cryptoniscus passes into a further larval stage, the Bopyrus, which performs the function of the male, and upon which the female organisation is imposed as the parasitic habit is assumed. The following is a list of the Epicarida with the Crustacea which serve as their hosts[106]:— Cryptoniscina │Microniscidae │on Copepoda. „ │Cryptoniscidae │on Ostracoda. „ │Liriopsidae │on Rhizocephala. „ │Hemioniscidae │on Cirripedia. „ │Cabiropsidae │on Isopoda. „ │Podasconidae │on Amphipoda. „ │Asconiscidae │on Schizopoda. Bopyrina │Dajidae │on Decapoda „ │Phryxidae │ „ „ │Bopyridae │ „ „ │Entoniscidae │ „ [Illustration: FIG. 85.—Epicaridian larva, probably belonging to one of the Cryptoniscina. _A_, 2nd antenna; _Ab_, abdominal appendages; _T_, thoracic appendages. (From Bonnier, after Hansen.) ] In all cases the first larval form which hatches out from the maternal brood-pouch is called the Epicaridian larva (Fig. 85). This little larva has two pairs of antennae, a pair of curious frontal processes, and a pair of mandibles. The other mouth-parts are missing; there are only six thoracic limbs, but the full complement of six biramous pleopods are present, and at the end of the body there may be a long tube of unknown function. As a type of the =Cryptoniscina= we may take the =Liriopsidae=,[107] parasitic on the Rhizocephala, which are, of course, themselves parasitic on the Decapoda, the whole association forming a very remarkable study in Carcinology.