Tylencholaimus imperanus Mohilal & Dhanachand, 2003

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 : 470-473

Tylencholaimus imperanus Mohilal & Dhanachand, 2003

( Figs. 11 & 12 )

Measurements: See table 6.

Description. Female: Small sized nematodes, slightly curved upon fixation; body cylindrical, tapering gradually towards the anterior extremity, posteriorly ending in a round hemispheroid tail. Cuticle with two distinct layers, 2 Μm thick at mid body 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 almost continuous with the body, about twice as wide as high, or about one-third of the body diameter at neck base; lips rounded and amalgamated; labial disc exceptionally enlarged, clearly offset from the rest of lip region and about two-thirds as wide as lip region diameter. Amphids with small aperture, about one-third as wide as lip region diameter at that level. Stoma a truncate cone. Odontostyle about as long as lip region diameter with slightly thickened tip, and a small aperture. Odontophore with small basal knobs, 0.8–1.2 times the odontostyle length. Guiding ring simple, refractive, at 0.5–0.7 times lip region diameter from anterior end. Pharynx consists of a slender and weakly muscular anterior part, expanding gradually into a cylindrical basal bulb, with thick-walled lumen, occupying about 43–51% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 57–61, DN = 60–65, S1N1 = 78–80, S1N2 = 81–83, S2N = 87–88, S2O = 88–89. Nerve ring located at 38–44% of neck length from anterior end. Cardia hemispherical, about one-sixth to one-third of the corresponding body diameter long.

Genital system monoprodelphic. Ovary reflexed, measuring 49–70 µm long, not reaching the oviduct-uterus junction; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 68–69 µm, its proximal and distal parts not differentiated; oviduct-uterus junction marked by well developed sphincter. Uterus short and tubular, measuring 25–31 µm. Posterior genital branch reduced to very short simple sac, 9–18 µm long. Vagina cylindrical; pars proximalis vaginae 4–6 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 5.5–7.6 and rectum 0.7–1.0 times anal body diameter long. Tail short, hemispheroid, 0.7–0.9 times anal body diameter long, with a pair of subdorsal caudal pores.

Male: General morphology similar to female but the posterior body region is more ventrally curved. In addition to the adcloacal pair, situated at 5 µm from cloacal aperture, there are three or four weakly developed ventromedian supplements, not clearly seen due to cuticle folds, one within the spicule range, two or three ventromedian supplements located outside the range; the first ventromedian supplement located 8 µm anterior to adclaocal pair. Spicules 1.7 times cloacal body diameters long. Lateral guiding pieces about one-fourth of the spicules length. Tail short, bluntly rounded, hemispheroid, 0.7 anal body diameter long.

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

Remarks. Tylencholaimus imperanus Mohilal and Dhanacahand 2003 is an atypical species of the genus, characterized by its unusual continuous lip region and a large labial disc, not fitting the typical cap-like pattern of the genus. Peña-Santiago (2008) also rightly pointed out this anomaly. However, our present specimens in all other features fit well under the generic diagnosis of Tylencholaimus . They also agree fairly well with the type specimens, except for having slightly smaller body size (vs 0.46–0.50 mm), lip region width (6.0–6.5 vs 4.8–5.6 µm), smaller amphid aperture (vs half as wide as corresponding body width), slightly longer odontostyle (vs 4.8 µm), longer prerectum (vs 33.6–35.2 µm) and the presence of male. The shape of the female tail is slightly different, in the original description the tail seems to be conoid rounded ( Fig 1 E of Mohilal & Dhanachand, 2003), rather than hemispheroid as mentioned in their description, however in our specimens it is typically hemispheroid. The male has been recorded here for the first time in this species. Although our specimens originated from the same region of India from where the original specimens were collected, these minor differences are considered here as intraspecific variations.

Figures

FIGURE 1. Tylencholaimus proximus Thorne, 1939. A. Entire female; B. Anterior region; C. Anterior end showing amphid; D. Pharyngeal region; E. Pharyngeal bulb; F. Female genital system; G. Female posterior region.

FIGURE 11. Tylencholaimus imperanus Mohilal & Dhanachand, 2003. A. Entire female; B. Anterior region; C. Anterior end showing amphid; D. Pharyngeal region; E. Pharyngeal bulb; F. Female genital system; G. Female posterior region; H. Male posterior region.

FIGURE 12. Tylencholaimus imperanus Mohilal & Dhanachand, 2003. A. Anterior region; B. Anterior end showing amphid; C. Pharyngeal bulb; D. Pharyngeal expansion; E. Female genital system; F. Vulval region; G. Female posterior region; H. Male posterior region. (Scale bar A, B, D, F = 10 µm; C, E, G, H = 20 µm)