Chætopods

Chætopods (Gr., 'bristle-footed'), a class of worms including familiar types like the Earthworm, the Fisherman's Lobworm, and the Sea-mouse. They are often included under the title of Annelids or ringed worms. The body consists of numerous more or less similar joints; and the locomotor organs are furnished with or represented by bristles. The class is split into two main orders of Oligochaeta and Polychaeta, of which the latter is much the larger. The Oligochaeta have very rudimentary locomotor structures, which are in fact reduced to bristles; they are fresh-water or subterranean in habit; the familiar earthworm (Lumbricus) and certain river and pond worms (e.g. Tubifex and Nais) are common representatives. The Polychaeta are, with three or four exceptions, marine; the bristles, which are numerous, are fixed in special locomotor outgrowths; and many other characters, such as the possession of antennæ, gills, &c., distinguish them from the earthworm order, and are in obvious association with their very different habits. Many of them, described as errant, lead a free life, and are carnivorous in their diet. The common Nereis, or Alitta, and the Sea-mouse (Aphrodite) are good examples. A large number, however, are sedentary in habit, vegetarian in diet, and often inhabit tubes. The lobworm (Arenicola), the common Serpula, and Terebella are characteristic types. To the two main orders of Chætopods above mentioned, the parasitic Myzostomata causing 'galls' on feather-stars (Crinoids), and the primitive aberrant Saccocirrus must be added. Polygordius is another common marine worm which, along with a few others, is usually regarded as a survival of the ancestral Chætopods or Annelids. See EARTH-WORM, LOBWORM, SEA-MOUSE, WORMS, &c.