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.

Almost every species of the Rhizocephala is subject to the attacks of Liriopsids, the latter fixing either on the Rhizocephala themselves, or else on the Decapod host at a point near the fixation of the Rhizocephalous parasite. An exceedingly common Liriopsid is Danalia curvata, parasitic on Sacculina neglecta, which is itself parasitic on the spider-crab, Inachus mauritanicus, at Naples. The adult Danalia is a mere curved bag full of eggs or developing embryos, and without any other recognisable organs except two pairs of spermathecae upon the ventral surface where the spermatozoa derived from the larval males are stored.

Fig. [86].—Inachus mauritanicus, ♀, × 1, carrying two Sacculina neglecta (a, b), and a Danalia curvata (c), the latter bearing two dwarf males.

In Fig. [86] is represented a female of Inachus mauritanicus which carried upon it two Sacculinae and a Danalia curvata, and upon the latter are seen two minute larval males in the act of fertilising the adult Danalia. The eggs develop into the Epicaridian stage, after which the larva passes into the Cryptoniscus stage (Fig. [87]). In this larval form the segments are clearly delimited; the only mouth-parts present are the mandibles, but there are seven pairs of thoracic limbs and the full number of pleopods. This Cryptoniscus stage is found in all the Epicarida, and only differs in detail in the various families.

Fig. [87].—Ventral view of Cryptoniscus larva of Danalia curvata, ♂, × 25.