ISOPODA, an extensive and varied group of Crustacea (q.v.) usually ranked as a suborder of the Arthroitraca or sessile eyed Malacostraca. The body is broad and flattened, and either short or elongated; the carapace is absent. or little developed; the thorax with seven free segments, each bearing a pair of walking limbs; the abdomen more or less shortened and bearing lamellar branchial appendages. The Isopoda are classi fied in several tribes and more than 30 families, embracing an enormous number of species. They vary: greatly in form and mode of life but all are of relatively small size and retiring habits. The vast majority are marine, but a few are inhabitants of fresh water or terres trial; the latter are familiar to everyone under the names wood-lice and pill-bugs. Most of the marine forms live a free life but conceal themselves in crevices or among sessile animals and plants, others bore into wood, some, as the gribble and its allies, being destructive to piling; many are commensal or parasitic, among the latter being the Cymothoirke which infest fishes and whales, and the greatly degenerated Bopyridee, which live in the branchial chamber of prawns and similar crustaceans. Consult
Packard, 'Zoology' (1887); Leichmann, Georg, zur Naturgeschichte der (Cassel 1891); Richardson, H., to Isopods of North America' (in Proceedings United States National Museum, Vols. XXI' and XXIII, 1899, 1901); Id., 'Isopods Collected at Hawaiian Islands by United States Steamer Albatross' (Washington 1903); id., (Contribu tion to the Natural History of the Isopoda' (ib., 1904); id., on the Isopoda of North America' (ib., 1905) ; id., 'Isopods Col lected in the Northwest Pacific' (ib., 1906).