ANNELIDA , a name derived from J . B . P .
See also:term Annelides, now used to denote a major phylum or division of coelomate invertebrate animals . Annelids are segmented
See also:worms, and differ from the
See also:Arthropoda (q.v.), which they closely resemble in many respects, by the possession of a portion of the coelom traversed by the alimentary canal . In the latter respect, and in the fact that they frequently develop by a
See also:metamorphosis, they approach the
See also:Mollusca (q.v.), but they differ from that
See also:group notably in the occurrence of metameric segmentation affecting many of the systems of
See also:organs . The
See also:wall is highly
See also:muscular and, except in a few probably specialized cases, possesses chitinous spines, the setae, which are secreted by the ectoderm and are embedded in pits of the skin . They possess a modified anterior end, frequently with
See also:special sense organs, forming a
See also:head, a segmented
See also:system, consisting of a pair of anterior, dorsally-placed ganglia, a
See also:ring surrounding the alimentary canal, and a
See also:double ventral ganglionated chain, a definite vascular system, an excretory system consisting of nephridia, and paired generative organs formed from the coelomic epithelium . They are divided as follows: (1)
See also:Haplodrili (q.v.) or Archiannelida; (2) Chaetopoda (q.v.); (3)
See also:Myzostomida (q.v.), probably degenerate
See also:Polychaeta; (4) Hirudinea (see CHAETOPODA and LEECH); (5) Echiuroidea (q.v.) . (P . C .
PETER ANNET (1693–1769)
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