CIRRIPEDIA, an order of entomostrac ous Crustacea (barnacles), sometimes ranked as a sub-class, always fixed in the adult stage, but with free-swimming larvahaving three pairs of appendages (nauplius) like other Crustacea. The typical barnacles have the body enclosed in a reduplication of the skin which secretes a calcareous shell, on which account they were classed with the Mollusc° until the discovery of their free-swimming larva led to a closer in vestigation of their structure. Owing to adapta tion to a sedentary life segmentation of the body has become obscure, and the six pairs of jointed biramous appendages, are mere fringed scoops for creating currents in the water. The eyes and other sense organs have likewise de generated, and most species are hermaphroditic. The barnacles are exclusively marine, and a great many are parasitic.
Four sub-orders are distinguished: (1) Tho racica, including the typical, free-living, shelled barnacles of which the sessile forms (Bala nidce, Coronulidce, etc.) are well known as rock and ship barnacles in which the animal is pro tected by a conical shell formed of several pieces, with a multivalve conical movable lid, having an opening through which several pairs of long, many-jointed, hairy appendages are thrust, thus creating a current which sets in toward the mouth. The young have oval bod ies, with a single eye, a pair of antenna, with three pairs of legs. After swimming about for some time it attaches itself by its antenna to some object, and now a strange backward meta morphosis begins. The body becomes enclosed
by two valves, the stalk by which it is anchored grows larger, the feet become more numerous and eventually the barnacle shape is attained. The goose-barnacle (Lofts) is not sessile, but is flat and triangular, and attached to floating bits of wood or seaweed by a long, large, soft stalk. (2) Abdominalia, parasitic barnacles, in which the sexes arc separate and very unequal in size. In this group is presented the remarkable phe nomenon of dwarfed complemental males dis covered by Darwin. The females live in bur rows in the shells of mollusks and other bar nacles, while the males are minute, lack mouth, digestive canal and appendages, and live, often several together, permanently attached to the female. (3) The Apoda, whose body is maggot shaped, are hermaphrodite and parasitic in other barnacles. (4) Rhizocephala: This group pre sents perhaps the most extreme cases of degen eration, through parasitism, known among ani mals. Sacculina, which attaches itself to the abdomen of the crab, is little more than a bag of genital organs which draws its nourishment from the tissues of its host by means of branch ing root-like processes which penetrate to every part of its body. Consult Darwin, (Mono graph of Cirripedia.'