CLASS I. CRUSTACEA (Lat. crusta, a crust). Respiration effected by gills or by the general body surface. There are two pairs of antennae. The locomotive appendages are more than eight, articulated to the segments of the thorax, and in most instances to those of the abdomen, the pairs generally being from five to seven. All these animals pass through a series of metamorphoses, and every embryonic organ or part is perma nently represented in some member of an lower order.. Authorities differ in the classifi cation of the erustacea, but that adopted here divides them into four sub-classes, com prising sixteen orders, Suit-CLASS I. EPIZOA (Gr. epi, upon, and soon,, animal). These animals are parasites in the adult state upon the bodies of fishes, but when young they are free-swimming, and have amteunm and eyes. This sub-elass contains titre.; orders: Order I. Ichthyophthira (Gr. icht/ws, a fish, and pktheir, it louse). These animals become attached to the skin, eyes, or gills of fishes by a sartorial mouth, or cephalic processes, or by a disk borne by the last pair of thoracic limbs, or by.hooklets at the extremities of the first pair. The males are usually not attached, hut adhere to the
females, which are much larger. In attaining the adult condition they pass through retrograde metamorphosis. See LERNEADA.
Order IL laiweephala (Gr•rhiza, and- Whale, head; root-headed). These animals, like those of the preceding order, are free-swimming when young. The larvae have ovate bodies, one eye, and a'dorsal shield. In the second, or man stage, they become inclosed in a bivalve shell and attach themselves to larger crustaceans. They then lose all their limbs, and appear like mere sacks. At the point of attachment they send tubular roots into tin.: body of the host, winding round its intestines.
Order III. Cirripcdire. Larva; free-swimming, but a cement-like secretion from a gland is discharged through the immune by which they become permanently attached to rocks, wood, cetaceans, turtles, other crustaceans, and sometimes jelly-fishes. The more important members are the acorn-shells and the barnacles. See BALAEUS, BARNA CLES, and CIRRHOPODA. The cirripedia are divided into three sub-orders, thoraeica, abdomiaalia, and apoda.