ANNEL'IDA, or ANNEn'inEs (from Lat. annulus, a ring), a small class of articulated animals, mostly included by Linnmus in his class vermes. They have a more or less elongated body, which is always composed of numerous rings. The first of these rings assumes., in most of them, the characters of a head, but in some there is no proper head. They have no articulated limbs, but most of them are provided with bristles and hairs, often in numerous bundles, which are of use to them in locomotion; some, which want these, are furnished with suckers at the extremities, and employ them for this pur pose; some remain fixed in one place. Their bodies are always soft, and without external or internal skeleton; but some of them form for themselves a calcareous cover ing by exudation, others form coverings partly by exudation and partly by agglutina tion. Their blood is generally red, but not from red corpuscles, as in the vertebrate animals; sometimes it is greenish or yellowish. Their nervous system is simple. Many
of them have eyes, and many have tentacula. Most of them live in water, and of these the greater part inhabit the sea. Those which live in water breathe by gills, which are variously formed and placed; some which are terrestrial, as earthworms, have, instead of gills, numerous small respiratory sacks. They are all hermaphrodite; most of them, however, requiring mutual fecundation, and most of them are oviparous. They feed in general upon other animals, and some of them live by sucking blood. They are now' divided into four orders: 1. Dorsibranekiata, having gill-tufts disposed regularly along the body, and composed of animals of comparatively active habits; 2. Tubleolts, having gill-tufts near the head, and provided with shells or other coverings; 3. Terricola', destitute of all external appendages except minute bristles, and breathing by respiratory sacs; 4. Suetoria, destitute even of bristles, and provided with suckers.