(Müller, 1786) Dujardin, 1841
Body nearly cylindrical, length to width ratio 4-8:1, posterior half slightly widened sac-like, rear end broadly to narrowly rounded, contractile; starved specimens dorsoventrally flattened. Posterior end often attached to detritus. Macronucleus moniliform, composed of 8-25 nodules. Possibly several (about 13-18) micronuclei. Contractile vacuole in posterior end, with collecting canal extending anteriorly, latter sometimes originating from confluence of several vacuoles. Cortical granules in 2-3 irregular interkinetal rows. About 40 somatic kineties. Oral cavity triangular. Adoral zone of membranelles extending over 1/4-1/6 of body. Conspicuous undulating membrane on right of oral cavity. Apical membranelles (cirri) 4-5 in number, frontal, on right of oral cavity. Swims rather rapidly. Size in vivo about 300-560 x 45-100 µm.
Ref.: Kahl (1932).