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(Müller, 1773)

Body slender, lanceolate, flexible, highly contractile; posterior portion narrowly rounded to tail-like; neck longer than body, widened anteriorly and curved dorsally. Anterior and posterior body portion distinctly flattened, middle section of left side considerably vaulted (especially in well-fed and contracted specimens). Contracted specimens broadly lanceolate, with several longitudinal ribs on left side. Contractile vacuole subterminal; 6-8 µm long extrusomes rod-like in top view but distinctly curved in lateral view, ends tapering; found mainly along oral slit. Ciliary rows 6-13 in number, on right side, gradually abutting right perioral kinety anteriorly; several rows of short cilia on left side. Dorsal brush composed of 10-15 dikinetids with clavate cilia. Oral slit extends over 1/3-1/2 of body along ventral side of neck. Paralleled by three perioral kineties, i.e. rows 2 and 3 with normally long cilia on right and row 1 with short cilia on left side; kineties 1 and 2 composed of dikinetids and row 3 of monokinetids (Litonotus cygnus). Size in vivo 200-500 µm (extended), 100-200 µm (contracted). Because of marked contractility, very variable in shape and thus easily confused with other species. Litonotus cygnus described by Borror (1972a) belongs to a different species because it has 4-7 macronuclear nodules (Foissner et al., 1995).

Ref.: Dragesco and Dragesco-Kernéis (1986), Foissner et al. (1995).

Litonotus cygnus