Body oviform, with prominent oral cone. Macronucleus horseshoe-shaped to reniform. Contractile vacuole in posterior end. Resting extrusomes in oral cone and body 5-10 µm long; many granular mucocysts in cortex. 54-80(100) longitudinal basal body rows, only anterior portions (about 9-17 basal bodies long) ciliferous, forming single ciliary wreath. Dorsal brush posterior to ciliary wreath, composed of 4-5 short rows of paired basal bodies with bristle-like cilia. Circumoral kinety immediately anterior to ciliary band (Foissner et al., 1995). Swims to and fro, usually very rapidly. Size in vivo 50-120, usually 50-80 x 30-80 µm. Species apparently highly variable, comprising several rather similar varieties or species (Dingfelder, 1962; Foissner, 1979). Ingested phytoflagellates were previously (e.g., Schewiakoff, 1896; Fauré-Fremiet, 1924) possibly misidentified as zoochlorellae (Foissner et al., 1995).
Ref.: Foissner (1979), Dragesco and Dragesco-Kernéis (1986), Song and Wilbert (1989), Foissner et al. (1995).