Fig. [84].—Ligia oceanica, ventral and dorsal views, × 1. (From original drawings prepared for Professor Weldon.)
The related Ligidium is found far inland, but always in the neighbourhood of water. These two genera may be distinguished by the numerous joints in the flagellum of the second antennae, the flagellum being in all cases the portion of the antenna succeeding the long fifth joint. Philoscia muscorum occurs usually near the coast, but it is also found inland in England under trees in damp moss. This genus and the common Oniscus, found in woods, are distinguished by the presence of three joints in the flagellum of the second antenna. Philoscia can be distinguished from Oniscus by its narrower body and the pretty marbled appearance of its back. The genus Trichoniscus has four joints in the flagellum; various species are found in woods. In Porcellio and Armadillidium there are only two joints in the flagellum, while Armadillidium, the common garden wood-louse, can be distinguished from all others by the flattened shape of the uropods, and the habit of rolling up into a ball like an Armadillo.
There is also a very peculiar species, Platyarthrus hoffmannseggii, which occurs in England and Northern Europe, and always lives in ants’ nests. It is supposed that they serve as scavengers for the ants, which tend them carefully, and evidently treat them as domestic animals of some kind. The small creature is quite white and blind, and has exceedingly short antennae.
Sub-Order 6. Epicarida.
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 | ||
