Tylencholaimus cosmos ( Dhanam & Jairajpuri, 1999 ) Peña-Santiago, 2008

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: 466-469

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Tylencholaimus cosmos ( Dhanam & Jairajpuri, 1999 ) Peña-Santiago, 2008


Tylencholaimus cosmos ( Dhanam & Jairajpuri, 1999) Peña-Santiago, 2008 

( Figs. 9View FIGURE 9 & 10View FIGURE 10)

Measurements: See Table 5.

Description. Female: Slender nematodes of small size, 0.57–0.70 mm long; body cylindrical, tapering gradually towards both extremities, slightly ventrally curved upon fixation. Cuticle with two distinct layers, 2 Μm thick at midbody and 2–3 Μm on tail. Outer cuticle thin, finely striated; inner layer thick with distinct radial refractive elements. Lateral chords occupying about one-third of the midbody diameter. Lateral, dorsal and ventral body pores indistinct.

Lip region cap-like, offset by a slight constriction, 2.3–3.5 times as wide as high or about one-third of the body diameter at neck base; lips amalgamated, with their inner part somewhat elevated. Amphid aperture a small slit. Stoma a truncate cone. Odontostyle 1.0– 1.1 times the lip region diameter long, its aperture about one-fourth to onethird of the odontostyle length. Odontophore rod-like with minute basal thickenings, 1.1–1.4 times the odontostyle length. Guiding ring simple, refractive, at 0.6–0.7 times lip region diameter from anterior end. Pharynx consists of a slender and weakly muscular anterior part, expanding abruptly into a cylindrical basal bulb, with thick-walled lumen, occupying about 41–45 % of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 58–63, DN = 61–65, S 1 N 1 = 76–80, S 1 N 2 = 82–88, S 2 N = 93–95, S 2 O = 93–96. Nerve ring located at 40–44 % of neck length from anterior end. Cardia rounded, hemispheroid, about one-fourth to one-third of the corresponding body diameter long.

Genital system didelphic-amphidelphic. Ovary reflexed, measuring 47–67 µm long (anterior) and 32–78 µm long (posterior), in one specimen the posterior branch reaches back up to vulva; oocytes arranged in a single row except near tip. Oviduct measuring 54–64 µm (anterior) and 48–64 µm (posterior), joining the ovary subterminally, its proximal and distal parts not differentiated; oviduct-uterus junction indistinct. Uterus short and tubular, measuring 21–25 µm (anterior) and 15–20 µm (posterior). Vagina cylindrical; pars proximalis vaginae 5–7 µm long, its wall encircled by muscles; pars distalis vaginae short, 1–2 µm long with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 1.9–4.3 and rectum 0.8–1.2 anal body diameter long. Tail cylindrical to rounded-conoid, 1.0– 1.1 anal body diameter long; caudal pores indistinct.

Male: Not found.

Habitat and locality. Soil samples collected from the grassland of the Kaziranga National Park, Assam, India.

Remarks. Dhanam and Jairajpuri (1999) described Amphitylencholaimus cosmos  from the Malnad tracts of Karnataka, India. Peña-Santiago (2008), not accepting the generic status of Amphitylencholaimus  , transferred this species to Tylencholaimus  . The present specimens, though conforming well with the type population in general morphology, have a comparatively smaller body size (L= 0.57–0.70 vs 0.7–0.9 mm), comparatively smaller neck length (146–175 vs 179–207 µm) and shorter tail (16–18 vs 19–22 µm). Dhanam and Jairajpuri (1999) characterized this species as having a weakly non-muscular anterior slender part of pharynx expanding gradually to form the basal part. This is a very unusual feature for Tylencholaimus  . All the didelphic species of Tylencholaimus  with gradual expansion of pharynx have quite muscular anterior part while those having non-muscular anterior part have sudden expansion (figure 1 C of Dhanam & Jairajpuri 1999 also to some extent indicate a sudden expansion. In our specimens also the anterior slender part of pharynx is slender and weakly muscular abruptly expanding to form the basal muscular part. The nature of the amphid is reminiscent of the genera Promumtazium Siddiqi, 1982  and Tantunema Siddiqi, 1982  . As per their figure 1 B, the amphid aperture is quite small, about one-third of the corresponding body diameter instead of about half lip region diameter as stated in their description ( Dhanam & Jairjpuri, 1999). In the present specimens the amphid aperture is also a small slit.

Table 5. Morphometrics of Tylencholaimus cosmos (Dhanam & Jairajpuri, 1999) Peña-Santiago, 2008 (All measurements in µm)

616.5 ± 44.4 (572-705)
Guiding ring from anterior end
376.8 ± 28.2 (345-420)