Tylencholaimus proximus Thorne, 1939

Ahad, Sumaya & Ahmad, Wasim, 2016, Description of two new and six known species of the genus Tylencholaimus de Man, 1876 (Nematoda: Dorylaimida) with a diagnostic compendium and key to species, Zootaxa 4107 (4), pp. 451-490: 454-456

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Tylencholaimus proximus Thorne, 1939


Tylencholaimus proximus Thorne, 1939 

( Figs. 1View FIGURE 1 & 2View FIGURE 2)

Measurements: See Table 1.

Description. Female: Small sized nematodes, slightly curved ventrad upon fixation; body cylindrical, tapering gradually towards both extremities but more so towards the anterior end. Cuticle with two distinct layers, 2–3 Μm thick at midbody and 3–4 Μm on tail. Outer cuticle finely striated; inner layer thick with distinct radial refractive elements. Lateral chords occupying about 36–43 % of the midbody diameter. Lateral body pores distinct, 3–4 in the pharyngeal region, 4–5 between pharynx and vulva, and 4–5 between vulva and tail; dorsal and ventral body pores indistinct.

Lip region cap-like, offset by deep constriction, 2.2–3.2 times as wide as high or about one-third to two-fifths of the body diameter at neck base; lips moderately separated and angular. Amphids cup-shaped with aperture located at the level of cephalic constriction and occupying about one-half to two-fifths of lip region diameter. Stoma a truncate cone. Odontostyle 0.6–0.8 times the lip region diameter long, its aperture about one-fourth to onethird of the odontostyle length. Odontophore rod-like, with small basal knobs, 1.1–1.6 times the odontostyle length. Guiding ring simple, refractive, at 0.5–0.6 times lip region diameter from anterior end. Pharynx consists of a slender, slightly muscular anterior part, expanding gradually into a cylindrical basal bulb, with thick-walled lumen, occupying about 34–43 % of total neck length. Pharyngeal gland nuclei and their orifices are located as follows (after Loof & Coomans 1970): DO = 62–67, DN= 65–70, S 1 N 1 = 77–80, S 1 N 2 = 84–87, S 2 N = 88–91, S 2 O = 90–92. Nerve ring located at 33–43 % of neck length from anterior region. Cardia rounded, hemispheroid, about one-third to one-half of the corresponding body diameter long.

Genital system mono-prodelphic. Ovary reflexed, measuring 62–98 µm long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 68–98 µm, its proximal and distal parts not differentiated; oviduct-uterus junction marked by weak sphincter. Uterus short and tubular, measuring 14–35 µm. Posterior genital branch absent or reduced to a rudimentary sac, less than one-fifth to one-third of the corresponding body diameter. Vagina cylindrical; pars proximalis vaginae 4–5 µm long, its wall encircled by muscles; pars distalis vaginae short, 1.5–2.5 µm long with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 2.0– 3.5 and rectum 0.6 –1.0 anal body diameter long. Tail convex-conoid with bluntly rounded terminus, 1.0– 1.3 times anal body diameter long, with a pair of caudal pores on each side.

Male: Not found.

Table 1. Morphometrics of Tylencholaimus proximus Thorne 1939 

(All measurements in µm)

Habitat and localities: i). Soil around the roots of grasses (unidentified) from Saboo, Leh, Ladakh, Jammu and Kashmir, India.

ii). Soil around the roots of pine ( Pinus sylvestris  ) from the forest trees of Doodhpather, Budgam, Jammu and Kashmir, India.

Remarks. Thorne (1939) described T. proximus  from Utah, U.S.A. Coomans (1962) reported this species from Belgium. Loof (1971) redescribed it from Norway, while Thorne (1974) from U.S. A and Vinciguerra (1986) from Italy. Peña-Santiago and Coomans (1996) in their revision of the genus Tylencholaimus  made a detailed study of the type population as well as five different populations comprising over one hundred female specimens of this species from Spain. The morphometrics of the present populations conform well with those of the type population except in having a shorter rectum (vs 17.5–19 µm). The present specimens also agrees well with other earlier described populations. It also agrees fairly well with Spanish populations as well as a population from China described by Li et al. (2008). This species is reported for the first time from India.