Genus Trefusia de Man, 1893
Bognenia Allgén, 1932 .
Diagnosis (modified from Leduc 2013)
Trefusiinae . Cuticle smooth or striated. Six jointed outer labial setae situated in separate circle from the cephalic setae; the latter situated either slightly anterior to, at same level as, or posterior to amphids. Amphideal fovea circular, oval, unispiral, spiral, elongated or pocket-shaped. Buccal cavity small or minute, funnel-shaped, not cuticularized. Males with mid-ventral row of pharyngeal supplements that may be papilliform, setiform, or complex; sometimes two additional subventral rows are also present. Precloacal supplements usually present, papilliform or setiform. Arcuate or almost straight spicules, with or without capitulum; gubernaculum present or absent. Male reproductive system diorchic. Female reproductive system with two opposed and reflexed ovaries. Tail conico-cylindrical or filiform. Eighteen species.
Type species
Trefusia longicauda de Man, 1893 .
Other valid species
T. americana Keppner, 1992 .
T. axonolaimoides Allgén, 1953 .
T. conica Gerlach, 1957 .
T. cornea Gerlach, 1958 .
T. curvispiculosa Vincx & Vanreusel, 1989 .
T. filicauda Allgén, 1933 .
= T. longispiculosa Bresslau & Schuurmans Stekhoven, 1940 .
T. helgolandica Riemann, 1966 .
T. honessi Keppner, 1986 .
T. litoralis (Allgén, 1932) De Coninck & Schuurman Stekhoven, 1933 .
= Bognenia litoralis Allgén, 1932 .
T. longicorpa Keppner, 1986 .
T. multipapillatum Bouwman, 1981 .
T. piperata Leduc, 2013 .
T. pseudolitoralis Vitiello, 1970 .
T. schiemeri Ott, 1977 .
T. spatulata Keppner, 1992 .
T. varians Gerlach, 1955 .
T. zostericola Allgén, 1933 .
Species inquirendae
T. filum Schuurmans Stekhoven, 1942 .
T. longiseta Allgén, 1947 .
T. nidrosiensis Allgén, 1933 .
T. obtusicaudata Allgén, 1933 .
Remarks
Keppner (1992) and Leduc (2013) provided keys to the males of the genus based on Riemann (1966). De Coninck & Stekhoven (1933) synonymised Bognenia with Trefusia . No male specimens have yet been described for Trefusia varians . Trefusia filum, T. longiseta, T. nidrosiensis and T. obtusicauda were considered species inquirendae by Riemann (1966). The latter author also synonymised T. longispiculosa with T. filicauda . In his PhD thesis, Bussau (1993) described T. dominatrix Bussau, 1993 and T. attenuata Bussau, 1993, but these species are considered nomina nuda because the descriptions were not published.