Litinium Cobb, 1920

Tchesunov, Alexei V., Thanh, Nguyen Vu & Tu, Nguyen Dinh, 2014, A review of the genus Litinium Cobb, 1920 (Nematoda: Enoplida: Oxystominidae) with descriptions of four new species from two contrasting habitats, Zootaxa 3872 (1), pp. 57-74 : 58-59

Litinium Cobb, 1920 , emended diagnosis

(= Alaimonemella Allgén, 1935 , syn. Lorenzen, 1981: 304) Oxystominidae , Oxystomininae . Circles of six inner and six outer labial setae situated close together on the anterior end, subapically, with a circle of four cephalic setae posterior to the circles of inner and outer labial setae. Amphideal fovea situated between the circles of the outer labial and cephalic setae. Amphideal fovea varies in shape between species and may differ in males and females of the same species: may be ovoid with an anterior round aperture, horseshoe-like or crescent contoured or more complex. An only posterior antidromously reflexed ovary present; vulva shifted anteriorly. Tail never clavate, more or less short, cylindrical or occasionally conical, with rounded tip; terminal caudal capsule absent or weakly developed.

Type species: Litinium aequale Cobb, 1920 .

Ten valid species, from marine and brackish sediments.

Remark. Within Oxystominidae , Litinium is morphologically closest to Thalassoalaimus de Man, 1893, and differentiation of the two genera may be difficult. Thalassoalaimus is particularly characterized by having a conical tail with a terminal structural elaboration, with distinctly thickened inner cuticle of the tail tip forming a so called tail capsule. However, the tail capsule in some species may be poorly developed (e.g. Th. lissus Gagarin, 2009 ) or almost absent ( Th. tardus de Man, 1893). On the other hand, the newly described Litinium profundorum sp. n. also has a weak thickening of the inner cuticle layer of the tail tip (but the latter is rounded rather than conical). Differentiation of Litinium and Thalassoalaimus should be clarified in a further study of Thalassoalaimus species.