Litinium Cobb 1920
Creators: name: Leduc, Daniel
name: Zhao, Zeng Qi
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Nematoda
Adenophorea
Enoplida
Oxystominidae
Litinium

description: Litinium Cobb, 1920
Diagnosis (modified from Tchesunov et al. 2014)
Circles of six inner and six outer labial papillae (<2 µm) or setae (≥ 2 µm) situated close together on anterior end, subapically, with circle of four cephalic papillae or setae posterior to circles of inner and outer labial sensilla. Amphideal fovea situated between circles of outer labial and cephalic sensilla. Amphideal fovea varies in shape between species and may differ in males and females of same species: may be ovoid with anterior round aperture, horseshoe-like or crescent contoured or more complex. Only one posterior antidromously reflexed ovary present; vulva shifted anteriorly. Tail never clavate, more or less short, cylindrical with rounded tip, occasionally conical or conico-cylindrical with pointed tip; terminal caudal capsule (thick cuticular lining at tip of tail) absent or weakly developed.
Remarks
The amphid of some species of Litinium Cobb, 1920 is described as being “horseshoe-shaped”. In the new species, our observations indicate that it is the superimposition of the amphideal aperture contour over the larger amphideal fovea contours that creates the appearance of a horseshoe-shaped structure. Whether this is also the case in other species of Litinium remains to be clarified.
There has been some confusion regarding the definitions of Litinium and Thalassoalaimus. The diagnoses provided by Smol et al. (2014) indicate that the two genera differ in the shape of the amphids (pocketshaped amphideal fovea and slit-like aperture in Thalassoalaimus vs horseshoe- or heart-shaped fovea and round aperture in Litinium) and presence (Thalassoalaimus) or absence (Litinium) of a caudal capsule. However, we note that the pocket-shaped amphideal fovea and slit-like aperture in Litinium subterraneum Tchesunov, Mokievsky & Nguyen Vu Thanh, 2010 is identical to that of Thalassoalaimus. On the other hand, Litinium profundorum Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014 has a weak thickening of the inner cuticle layer of the tail tip resembling a caudal capsule but is characterised by a horseshoe-shaped amphideal fovea typical of the genus Litinium. Most recently, Martelli et al. (2017) used the presence or absence of a caudal capsule as the sole distinguishing feature between the two genera, resulting in the transfer of several species of Thalassoalaimus to Litinium. Some of the newly transferred species, namely L. aceratus (Vitiello, 1970) Martelli, Lo Russo, Villares & Pastor de Ward, 2017 and L. longicaudatus (Vitiello, 1970) Martelli, Lo Russo, Villares & Pastor de Ward, 2017, as well as L. gludi sp. nov., are characterised by conico-cylindrical tails, which require the genus diagnosis of Tchesunov et al. (2014) to be emended. In addition, L. longicaudatus, L. qangi Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014, L. curticauda Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014 and L. gludi sp. nov. are characterised by papillose to short setose labial sensilla (0.5–2.5 µm long), unlike all other species of the genus which have exclusively setose (> 2 µm) labial sensilla.
List of valid species
L. abyssorum Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014
L. aceratus (Vitiello, 1970) Martelli, Lo Russo, Villares & Pastor de Ward 2017
L. aequale Cobb, 1920
L. australis Martelli, Lo Russo, Villares & Pastor de Ward, 2017
L. bananum Gerlach, 1956
L. curticauda Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014
L. dispariseta Yu & Xu, 2018
L. egregius (Steiner, 1916) Martelli, Lo Russo, Villares & Pastor de Ward 2017
L. gludi sp. nov.
L. longicaudatus (Vitiello, 1970) Martelli, Lo Russo, Villares & Pastor de Ward 2017
L. obtusilobus Bussau, 1993
L. paramontemari (Vitiello, 1970) Martelli, Lo Russo, Villares & Pastor de Ward 2017
L. parmatum Wieser, 1954
L. pirum (Lorenzen, 1969) Martelli, Lo Russo, Villares & Pastor de Ward 2017
L. profundorum Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014
L. quamgi Tchesunov, Nguyen Vu Thanh & Nguyen Dinh Tu, 2014
L. setosus (Timm, 1967) Martelli, Lo Russo, Villares & Pastor de Ward 2017
L. subterraneum Tchesunov, Mokievsky & Nguyen Vu Thanh, 2010
L. volutum Gerlach, 1962
description: Published as part of Leduc, Daniel & Zhao, Zeng Qi, 2021, Litinium gludi sp. nov. (Nematoda, Oxystominidae) from Kermadec Trench, Southwest Pacific Ocean, pp. 138-154 in European Journal of Taxonomy 748 (1) on pages 142-143, DOI: 10.5852/ejt.2021.748.1347, http://zenodo.org/record/4745050