Deontostoma Filipjev 1916

Genus Deontostoma Filipjev, 1916

Diagnosis (modified from Hope (1967)). Cephalic capsule without ventral tropis. Mouth opening enclosed by one dorsal and two sub-ventral microlabia; buccal cavity with or without dorsal onchium. Pharyngeal pigment spot usually present, and when present, always cyathiform and with lens-like structure. Gubernaculum parallel to spicules, with paired apophyses directed dorsally or anterodorsally, never at right angle to corpus; often with elongated, anteriorly-directed crurae near distal end or middle region of corpus. Caudal glands extending anterior to anus/cloaca.

Remarks. The genus Deontostoma was last revised by Hope (1967), who argued that the presence or absence of the tropis (a process arising from the internal surface of the ventral side of the cephalic capsule) is the most reliable character for differentiating between Deontostoma and the closely related genus Thoracostoma Marion 1870. In an earlier revision, Platonova (1962) suggested that differences in spicule shape may also help differentiate the two genera, but Hope (1967) noted that several exceptions exist, and spicule shape is therefore not considered a useful character.

The following list of valid Deontostoma species is based on the revisions of Platonova (1962) and Hope (1967), as well as subsequent species descriptions by Hope (1974; 1977), Vitiello (1975), Coles (1977), Pastor de Ward (1995), and Gagarin (2008). The list follows Wieser (1953), who considered D. anchorilobatum Allgén 1947 and D. elongatum Ditlevsen 1926 synonymous with D. arcticum Saveljev 1912, and D. polare Cobb 1914 synonymous with D. antarcticum Linstow 1892. Deontostoma montredonense Marion 1870 was considered doubtful by Wieser (1953), and is therefore not included in the list.