Chaetosomatida

CHAETOSOMATIDA, a small group of minute, free-living, aquatic organisms which are usually placed as an annex to the 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-water. The genus Chaeto soma, have swollen heads. The third genus Rhabdogaster has no such distinct head, though the body may be swollen anteriorly. The mouth is anterior and surrounded by a ring of spicules or a half-ring of hooks.

Scattered hairs cover the body. Just in front of the anus there is in Cizaetosorna a double, and in Tristicochaeta a triple row of about fifteen stout cylindrical projections upon which the animals creep. The females are a little larger.