Litinium curticauda Tchesunov, Nguyen Dinh Tu & Nguyen Vu Thanh

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 : 64-66

Litinium curticauda Tchesunov, Nguyen Dinh Tu & Nguyen Vu Thanh sp. n.

Fig. 3 , Table 2

Quang Ngo Xuan et al., 2008: 7–9, fig. 4 ( Litinium sp. 2 )

Material. One holotype male. The specimen is deposited in Vietnam National Museum of Nature (18 Hoang Quoc Viet, Caugiay , Hanoi, Vietnam) with the slide number VNMN .0010 .

Locality. South Vietnam coast, Dong Nai River Delta , Can Gio National Reserve . 10°32'176''N and 106°45'919''E, 0.5 m deep. Sediment consisted of silt and clay (80.5%) and sand (19.5%). NaCl content 13.5‰.

Description of the holotype. Body long, cylindrical, gradually attenuated from the cardia level to the anterior cephalic apex. Cuticle very thick and smooth over the entire body. Cuticle anterior to the amphideal fovea 1.6 µ m thick, posterior to the amphideal fovea 2.5 µ m, posterior to the cardia 2.6 µ m, tail terminal cuticle 4.7 µ m.

Both six inner and six outer labial sensilla united in a crown of twelve equal, short setae situated about 2.5 µ m from the cephalic apex. Four very short cephalic setae situated posterior to the anterior crown of setae at the level of the posterior margin of the amphideal pouch. Each cephalic seta implanted in anterior end of a longitudinal ‘slit’ in the cuticle. Amphideal fovea rather large, situated between the crown of the inner plus outer setae and the cephalic setae. The amphideal fovea longitudinally ovoid in shape, with a distinct peripheral cuticular ridge surrounded the fovea anteriorly and laterally but not posteriorly. Amphideal aperture transversally oval, at the anterior end of the fovea. Some minute papillae scattered along lateral sides of the preneural body.

Distinct midventral excretory pore with a thin duct situated at a quarter of the distance from the cephalic apex to the nerve ring. Apparently part of a ventral gland; neck however only traced a short distance posterior; cell body not clear. A second less distinct midventral pore with a thin intracuticular canal but without any signs of a duct is present; situated 27 µ m posterior to the anterior ventral pore.

Mouth opening tiny and structurally simple, evidently lipless. Buccal cavity not developed, anteriormost internal cuticle thin and not differing from the following cuticular lining of the pharynx. For most of its length, pharynx is slender, with barely discernible transverse striation. At the posterior end, the pharynx widens and has clear transverse muscular striations. Cardia short, semicircular and surrounded by intestinal tissue. Internal canal of the cardia thin and straight. Internal lumen of the midgut filled partly with fine granular non-refractive material.

Anterior testis with distinct longitudinal fibres (spermatozoa?), situated to the right of the intestine. Posterior testis absent. Spicules short and slightly arcuate, broad, with internal longitudinal stripes, with both anterior and posterior spicule ends pointed. Gubernaculum comprises a pair of short cuticular bars. Two short midventral precloacal supplementary setae: anterior one at the level of the posterior end of the spicules, 39 µ m from the cloaca, posterior one just anterior to the cloacal opening, 5 µ m from the cloaca. Both precloacal midventral setae 1.7 µ m long. Distinct bursal musculature in the tail.

Tail very short and terminally rounded, cuticle terminally slightly thickened. Spinneret not apparent as such except for a thin subterminal intracuticular canal. Two (one lateral and one latero-dorsal) papillae on the tail.

Remark. The specimen described above is evidently conspecific with the male denoted as Litinium sp. 2 by Quang et al. (2008). Dimensions of both males are presented in Table 3 .

Diagnosis. Litinium . Body length 2866–3431 µ m, a 63–67.6, c 110–119, c' 0.83–0.94. Inner labial, outer labial setae short, 1.4–1.5 µ m, cephalic setae 1.5–2.1 µ m. Amphideal fovea ovoid in outline, with horseshoe-shaped cuticular rim. Cephalic setae at the level of the posterior end of the amphideal fovea. Two midventral supplementary setae, anterior one situated at the level of anterior tips of the spicules, posterior one just anterior to the cloacal opening.

Differential diagnosis. Litinium curticauda sp. n. belongs to a group of species having ovoid amphideal fovea with round to oval anterior apertures ( L. aequale , L. parmatum , L. quangi , L. subterraneum ). The new species differs from L. parmatum and L. subterraneum in having a short rounded tail (c' 0.83–0.94 vs 4.2, 3.47–3.48, respectively), from L. aequale , L. parmatum , L. subterraneum with shorter anterior sensilla (1.4–1.5 µ m vs 9–10 µ m, 6.9–18 µ m, 2.5–4 µ m, respectively). The species most similar to L. curticauda is the sympatric L. quangi ; differing from it by having two precloacal setae instead one, index a (63–67.6 vs 103–118), c' (0.83–0.94 vs 1.36–1.63), distance from the cephalic apex to the ventral pore (39.5–48 µ m vs 68–75 µ m), and length of spicules (46.5–49 µ m vs 30–33 µ m).

Etymology. Species name means 'short tail'.

Figures

FIGURE 3. Litinium curticauda sp. n., holotype male. A: entire; B: anterior body; C: anterior end; D: posterior end. Arrow indicates a longitudinal slit in the cuticle where cephalic seta is inserted (lo. sl.). Scale bars: A 500 µ m; B 100 µ m; C, D 20 µ m.

Tables

TABLE 2. Morphometry of Litinium curticauda sp. n. Measurements in µ m.

Characters	Male specimens
	Holotype male	Litinium sp. 2, after Quang et al., 2008
L	2866	3431
a	67.6	63
b	9.67	9.8
c	119	110
c'	0.83	0.94
diam.c.s.	6.9	?
diam.am.	11.3	15.9
diam.n.r.	31.5	40.7
diam.ca.	37.6	45.2
diam.midb.	42.4	52.5
diam.ani	29	33.3
i.l.s.	1.4	?
o.l.s.	1.4	?
c.s.	1.5	2.1
dis.c.s.	11.4	?
dis.am.	3.7	6.1
am.l.	7.2	12
am.w.	6	5.2
dis. v.pore	39.5	48
spic.arc.	49	46.5