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CHAETOSOMATIDA

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Originally appearing in Volume V05, Page 799 of the 1911 Encyclopedia Britannica.
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CHAETOSOMATIDA , a small See also:

group of See also:minute, See also:free-living, aquatic organisms which are usually placed as an annex to the See also:Nematoda. Indeed Mechnikov, to whom we owe much of our knowledge of these forms, calls them " creeping Nematoda." They are usually found amongst seaweed in temperate seas, but they are probably widely distributed; some are fresh-See also:water. The genus Chaetosoma, with the two See also:species Ch. claparedii and Ch. ophicephalum and the genus Tristicochaeta, have swollen heads. The third genus Rhabdogaster has no such distinct See also:head, though the See also:body may be swollen anteriorly. The mouth is terminal and anterior and surrounded by a See also:ring of spicules or a See also:half-ring of hooks. Scattered hairs See also:cover the body. Just in front of the anus there is in Chaetosoma a See also:double, and in Tristicochaeta a triple See also:row of about fifteen stout cylindrical projections upon which the animals creep. The See also:females are a little larger than the See also:males; in Ch. claparedii the former attain a length of 1.5 mm., the latter of I.I2 mm. The mouth opens into an See also:oesophagus which passes into an See also:intestine; this opens by a ventral anus situated a little in front of the posterior end. The testis is single, and its duct opens with the anus, and is provided with a couple of spicules. The ovary is double, and the oviducts open by a median ventral See also:pore about the See also:middle of the body; in this region there is a second swelling both in Chaetosoma and in Rhabdogaster. The last-named See also:form is in the See also:female o•36 mm. in length.

In it the hairs are confined to the dorsal middle See also:

line and the creeping setae are hooked, of a finer structure than in Chaetosoma, and situated so far forward that the vagina opens amongst them. Ch. ophicephalum has been taken in the See also:English Channel. See E. Mechnikov, Zeitschr. wiss.- Zool. xvii., 1867, p. 537; Panceri, Atti Acc. Napoli, vii., 1878, p. 7. (A. E.

End of Article: CHAETOSOMATIDA

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