Urosoma emarginata (Stokes, 1885) Berger, 1999

Urosoma is a hypotrich ciliate with a tapered, tail-like posterior and cirri in the Oxytricha pattern (2 rows of marginal cirri, 18 frontal and ventral cirri). It has two elongate macronuclei. Adoral membranelles and undulating membranes are in the Gonostomum pattern (instead of an open “question mark” shape around the oral opening, the membranes follow the line of the AZM, giving the anterior of the hypotrich a distinctive snub-nosed appearance).

Urosoma emarginata is easily distinguished from other members of the genus by the notch in its “tail.” The species was first described by Alfred Stokes as Opisthotricha emarginata, but Helmut Berger moved it to Urosoma (Monograph of the Oxytrichidae , p. 409). It has sometimes been considered a synonym of Urosoma macrostyla, but Berger affirms its distinctness.