Tylencholaimus striatus, Islam & Ahmad, 2021

Islam, Md Niraul & Ahmad, Wasim, 2021, Five new and five known species of the genus Tylencholaimus de Man, 1876 (Nematoda: Dorylaimida: Tylencholaimoidea) from Western Ghats of India, European Journal of Taxonomy 774 (1), pp. 58-105 : 92-97

Tylencholaimus striatus sp. nov.

urn:lsid:zoobank.org:act:AB28078B-AE98-4000-844C-B8823170F355

Figs 13–14 , Table 9

Diagnosis

Tylencholaimus striatus sp. nov. is characterized by having small sized, robust body, 0.30–0.34 mm; distinctly striated cuticle; lip region set off by slight constriction; odontostyle 5.0–5.5 μm; odontophore about as long as odontostyle with minute basal knobs, total stylet length 10–11 μm; pharynx with slender anterior part, expanding abruptly into a cylindrical basal bulb occupying about 36–41% of total neck length; female genital system monodelphic-prodelphic; posterior genital branch reduced to a small uterine sac, 0.4–0.6 times the midbody diameter; vulva a transverse slit and tail short, cylindroid to conoid with bluntly rounded terminus.

Etymology

The new species is named Tylencholaimus striatus sp. nov. because of its distinctly striated cuticle.

Material examined

Holotype INDIA • 1 ♀; Karnataka State, Kodagu district, Bhagamandala ; 12°23′29.1″ N, 75°31′50.0″ E; 5–15 cm depth; 15 Nov. 2016; roots of shrubs and forest trees (unidentified); slide reference number AMU/ZD/ NC/ Tylencholaimus striatus /1.

Paratypes INDIA • 4 ♀♀; same collection data as for holotype; slides reference number AMU/ZD/NC/ Tylencholaimus striatus /2–3 • 1 ♀; same collection data as for holotype; slide reference number AMU/ ZD/NC/ Tylencholaimus striatus /4, nematode collection of the Zoological Survey of India, Kolkata, India .

Type habitat and locality

Soil samples collected from around the roots of shrubs and forest trees (unidentified) from Bhagamandala, Karnataka State.

Description

Female

Small sized nematodes, slightly curved ventrad to open C-shaped upon fixation; body cylindrical, tapering gradually towards both extremities but more so towards the anterior end. Cuticle with two distinct layers, 1.0–1.5 μm thick at midbody and 2.0–2.5 μm on tail. Outer cuticle strongly striated; inner layer thick, loose, irregular outline with distinct radial refractive elements. Lateral chords occupying about 26–36% of midbody diameter. Lateral dorsal and ventral body pores indistinct. Lip region caplike, offset by slight constriction, 1.7–2.0 times as wide as high or about ⅓ to 2/5 of the body diameter at neck base. Lips rounded, amalgamated, inner part slightly elevated. Labial and cephalic papillae distinct but not interfering with the labial contour. Amphids cup-shaped, their aperture occupying about ⅓ to 2/5 of lip region diameter. Stoma a truncate cone. Odontostyle 0.8 times the lip region diameter long, its aperture about ⅓ of the odontostyle length. Odontophore rod-like, as long as odontostyle, with minute basal knobs. Guiding ring simple, refractive, at 0.7–0.9 times the lip region diameter from anterior end. Pharynx consisting of a slender, slightly muscular anterior part, expanding abruptly into a cylindrical basal bulb, with thick-walled lumen, occupying about 36–41% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 62–66, DN = 65–69, DO–DN = 2.2–3.1, S1N1 = 74–77, S1N2 = 78–82, S2N = 89–91, S2O = 91–92. Nerve ring at 39–44% of neck length from anterior end. Cardia rounded conoid, about ⅓ of the corresponding body diameter long.

Genital system monodelphic-prodelphic. Ovary reflexed, measuring 29–47 μm long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 42–54 μm, its proximal and distal parts not differentiated. Oviduct-uterus junction marked by well-developed sphincter. Uterus short, measuring 19–26 μm. Posterior genital branch reduced to a small uterine sac, 5.5–10.0 μm or about 2/5 to 3/5 of the corresponding body diameter long, rarely absent (n = 2). Sperm cell not present in the genital tract. Vagina cylindrical, extending inwards, 7.5–9.0 μm or about ½ (49–55%) of midbody diameter; pars proximalis vaginae 5.0–6.0 × 2.5–3.5 μm, encircled by circular muscles; pars distalis vaginae short, 2.5– 3.0 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 2.6–4.5 and rectum 1.1–1.5 times anal body diameter long. Tail convex-conoid with bluntly rounded terminus, 1.1–1.3 times anal body diameter long, with a pair of caudal pores on each side.

Male Not found.

Taxonomic remarks

In its small sized body, lip region without labial disc, abrupt pharyngeal expansion, mono-prodelphic gonad and short conoid tail, the new species comes close to T. minutus Vinciguerra, 1986 and T. gallaicus Seijas et al., 2007 but differs from the former in having a comparatively smaller body size (0.30–0.34 vs 0.37–0.52 mm); absence of labial disc (vs labial disc present); lower b value (2.5–2.7 vs 2.7–3.5); slightly shorter pharynx (116–126 vs 121–161 μm), shorter pharyngeal expansion (36–41 vs 42–46% of total neck length); presence of well-developed sphincter (vs sphincter weakly developed); shorter and differently shaped tail (12–15 vs 15–18 μm, convex-conoid vs conical with finely rounded terminus) and absence of male (vs present).

The new species differs from T. gallaicus in having a posterior vulva position (V = 68–72 vs 60.3–66.7); shorter tail (12–15 vs 20–28 μm); higher c (23–27 vs 12.3–19.0); lower c’ (1.1–1.3 vs 1.6–2.4) ratios and absence of male (vs present).

In the presence of monodelphic genital system and conoid tail, the new species comes close to T. decens Andrássy, 1991 and T. mirabilis de Man, 1876 , but differs from T. decens , in having a comparatively shorter body size (0.30–0.34 vs 0.68–0.80 mm); narrower lip region (5.5–6.0 vs 8.0–10 μm); lower b value (2.5–2.7 vs 3.2–3.4); shorter odontostyle (5.0–5.5 vs 7.0–8.0 μm) and odontophore (5.0–5.5 vs 8.0–9.0 μm); shorter pharynx (116–126 vs 207–232 μm); shorter pharyngeal bulb (46–51 vs 99–115 μm); shorter tail (12–15 vs 19–21 μm), lower c (23–27 vs 31–38) and slightly higher c’ (1.1–1.3 vs 0.9–1.1) ratios.

The new species differs from T. mirabilis in having a smaller body size (0.30–0.34 vs 0.69–1.0 mm), narrower lip region (5.5–6.0 vs 8.0–10 μm); lower b value (2.5–2.7 vs 2.9–4.4); shorter odontostyle (5.0–5.5 vs 6.0–7.0 μm) and odontophore (5.0–5.5 vs 8.5–11.5 μm); shorter pharynx (116–126 vs 186– 254 μm), shorter pharyngeal expansion (46–51 vs 88–112 μm); shorter tail (12–15 vs 24–34 μm) and absence of male (vs present).

Figures

Fig. 13. Tylencholaimus striatus sp. nov., ♀. A, D–F, H. Paratype 1 (slide 2). B–C. Holotype (AMU/ ZD/NC/Tylencholaimus striatus/1). G. Paratype 5 (slide 4). A. Entire specimen. B. Anterior region C. Anterior region showing amphid. D. Expanded part of pharynx. E. Pharyngeal region. F–G. Genital system. H. Posterior region.

Fig. 14. Tylencholaimus striatus sp. nov., ♀ (LM photographs). A, C, I. Paratype 1 (slide 2). B, H. Holotype (AMU/ZD/NC/Tylencholaimus striatus/1). D. Paratype 2, (slide 2). E, G. Paratype 5 (slide 4). F. Paratype 3 (slide 3). J. Paratype 4, (slide 3). A. Entire specimen. B–C. Anterior region. D. Anterior region showing amphid. E. Pharyngeal region. F. Expanded part of pharynx. G–H. Genital system. I–J. Posterior region. Scale bars: A = 20 μm; B–J = 10 μm.