CLASS II. ANNELIDA. by Linnwas in his class rerme,Q. See ANNELIDA. The members of this class have distinct segments, each segment usually corresponding with a single pair of ganglia in the double ventral cord, all the segments being similar except those at the anterior and posterior extremities. Each segment may have a pair of lateral appendages, but they are never articulated with the body. There are four orders: Order I. Hirudinea (diseophara. or surtoriallerehrs). These animals are characterized by having a locomotive and adhesive sucker posteriorly, or at both extremities, and by having no bristles or foot-tubercles. They are hermaphrodite, and the young undergo no metamorphosis. See Ltt:eu.
Order II. Oligoehata (Gr. oligos, few; ehatte, hair), earth-worms—lumbricider; water worms—nvididte; and mud-worms—Umictila. These have locomotive appendages in the form of bristles. See EARTH-WORM.
Order III. ?Vitola (Lat. tuba, a tube). These annelides inhabit tubes, sometimes calcareous and secreted by the animals; sometimes composed of a glutinous secretion mixed with grains of sand, forming a cement. Sexes separate; young passing through a metamorphosis. There is a pseudo-hemal system, usually containing red blood. some times green. Respiratory organs in spiral, funnel-shaped tufts, or branchi:e. See TUBICO1.2E and SERPULA.
Order iv: Errantla (Let. erm, I wander), nereidea, dorsibranchiata. Respiratory organs in the form of branchial tufts, arranged along the back and sides of the body. This order includes the sand-worms, sea-worms, and sea-mice. Body soft, integument having a great number of segments; head provided with eyes, and two or more feelers, which are not jointed like the antenna: of crustaceans; mouth on the under surBfee of the head, and having one or more pairs of horny, lateral-working jaws; stomach ;lad intestine usually distinct, and hued with ciliated epithelium; periviseeral cavity tilled with a colorless fluid containing corpuscles (Owen). The pseudo-fitnal system consists
of a dorsal and a ventral vessel connected by transverse branches. There are pulsating dilations at the base of the bmuchial tufts. The circulating fluid is usually red. but is yellow in some, as the sea-mouse (q.v.). On account of the position of the tufts the members of. this order are sometimes called dorsibranehlate, or notobrauchiate. The nervous system in errantia consists of a double, ventral cord, with two ganglia to each segment or somite. The cerebral ganglia, situated in front of the gullet, are large. and send filaments to the eyes and feelers. Among the errantia is the common lob-worm, often used by fishermen for bait. It lives in deep burrows formed in the sand on the sea-shore, the animal passing the sand through its body to get nourishment. There are thirteen pairs of brauchke or gills, placed one of each pair on zi side, in the middle por tion of the body. In the nereidm, or sea centipedes, the head is distinct, and has eyes and feelers, the mouth having a large proboscis with horny jaws. In the ennieca the branchite are large, and the mouth has from seven to nine horny jaws. The euniee gigantea often has over 400 segments, and is sometimes more than 4 ft. long. Traces of errantia are found in the Cambrian rocks and other formations up to the present thne, and the tnbicola have left thin sheaths in all formations from the Silurian upwards. See EIIG-WORM, LOB-WORM, NEREIS, and PALOLO.