Litonotus cygnus (Müller, 1773) Kahl, 1931

Lionotus cygnus — Bílý et al. 1952: 81; Hanuška 1962: 822; Hanuška 1967: 927.

Litonotus cygnus — Matis 1977: 25; Tirjaková & Matis 1987: 9; Matis 1988: 58; Matis & Straková-Striešková 1991: 114; Matis & Tirjaková 1992: 52; Tirjaková 1993: 134; Matis & Tirjaková 1994: 58; Tirjaková 1997a: 16; Tirjaková 1997b: 27; Tirjaková 1998: 16; Tirjaková 2001: 15; Baláži & Matis 2002a: 155; Baláži & Matis 2002b: 9; Tirjaková 2003a: 37; Tirjaková 2003b: 20; Tirjaková & Stloukal 2004: 17; Tirjaková 2006: 9; Tirjaková & Vďačný 2013a: 670.

Nomenclature. Matis (1977) misdated L. cygnus with year 1786, and Matis (1988) and Matis & Tirjaková (1992) with year 1776. Tirjaková & Stloukal (2004) incorrectly used Foissner et al. (1995) as combining authors. However, Kahl (1931) already combined this species with the genus Litonotus, erroneously using “ Lionotus (Vibrio) cygnus (O. F. Müller), 1776 ”.

Main morphological characters (according to Foissner et al. 1995). Length 200–300 µm in vivo. Body fusiform, posteriorly tail-like when fully extended; highly contractile. Two macronuclear nodules with a single micronucleus in between. Contractile vacuole distinctly subterminal. Extrusomes rod-like and curved, about 6–8 µm long, attached along whole length of oral bulge and scattered in cytoplasm. Somatic ciliary pattern Litonotus - like; 6–13 right and about 5 left kineties.

Distribution. Litonotus cygnus was recorded in the benthos from the Hornád River near the village of Kubachy (Bílý et al. 1952); in the Nitra River and its two tributaries, the Handlovka stream and the Žitava River (Hanuška 1962); in the rivers Hnilec and Hornád as well as in their tributaries (Hanuška 1967); in the littoral of the water reservoir of Zemplínska Šírava during fall and spring (Matis 1977); in submerged, wet, and moist mosses from Slovenský Raj (Tirjaková & Matis 1987); in organic mud from activated sludge plants in Bratislava (Matis 1988); in the Teplý potok brook and thermal lakes in the Bojnice Spa at 16–42 °C and pH 5.6–7.5 (Matis & Straková-Striešková 1991); in the backwaters of the Danube River in Čičov (Matis & Tirjaková 1992); in the periphyton and benthos of the Turiec River (Tirjaková 1993); in small lakes in the inundation zone of the Morava River (Matis & Tirjaková 1994); in debris of the spring area below the Veľký Javorník, Malé Karpaty Mts (Tirjaková 1997a, Tirjaková & Stloukal 2004); in oligotrophic streams in the National Nature Reserve Rozsutec, Malá Fatra Mts (Tirjaková 1997b); in the benthos from tributaries of the Hron River (Tirjaková 1998); in the benthos from the Ružičkov prameň spring, High Tatra Mts (Tirjaková 2001); in the pelagial of the Morava River and Váh River near Komárno (Baláži & Matis 2002a); in the benthos from various localities in the Gidra River (Tirjaková 2003a); in the Stupavský potok brook (Tirjaková 2003b); in the spring area of the Hron River (Tirjaková 2006); in the sediment from the littoral zone of the upper Váh River (Tirjaková & Vďačný 2013a).