(Cohn, 1866)
Kahl, 1932
Body elongate rectangular, about anterior 1/3 attenuated (extent depending on nutritional state), posteriorly broadly rounded; flexible, fragile. Dorsoventrally flattened. Macronuclear nodules 16-64 in number; 2 micronuclei. Three frontal, 7-8 ventral, 2 pretransverse, 5(6) transverse cirri; 1 right and 1 left marginal cirral row not confluent posteriorly. Three dorsal kineties with long and fine cilia, perhaps 3 elongate caudal cirri. Adoral zone extending along left margin over 1/3-1/2 of body length, composed of about 40 thickened membranelles; undulating membranes short, on right of oral cavity. Quickly crawling forward and backward, frequently raises anterior portion above substrate, thigmotactic. Size in vivo 100-250 x 20-40 µm. Usually a mesopsammal species, but also found in the benthos and plankton. Very likely closely related to oxytrichids.
Ref.: Kahl (1932), Borror (1963, 1972b), Maeda and Carey (1984).