Tylencholaimus ibericus Peña-Santiago & Coomans, 1994

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 : 70-73

Tylencholaimus ibericus Peña-Santiago & Coomans, 1994

Fig. 5 , Table 4

Tylencholaimus ibericus Peña-Santiago & Coomans, 1994c: 355–358 .

Tylencholaimus japonicus Ahmad & Araki, 2003: 9–12 .

Tylencholaimus zhongshanensis Wu et al., 2019: 4–8 .

Tylencholaimus ibericus – Dhanam & Jairajpuri 1999: 3.— Ahad & Ahmad 2016: 364–466 . Tylencholaimus japonicus – Li et al. 2008: 2000 .

Material examined

INDIA – Kerala State • 2 ♀♀, 1 ♂; Thiruvananthapuram district, Ponmudi hill; 8º45′36.3″ N, 77º07′08.3″ E; 5–15 cm depth; 4 Nov. 2017; soil samples collected from around the roots of grasses and shrubs (unidentified); slides reference number AMU/ZD/NC/ Tylencholaimus ibericus /1–2 . – Karnataka State • 3 ♀♀; Kodagu district, Bhagamandala ; 12°23′29.1″ N, 75°31′50.0″ E; 5–15 cm depth; 8 Nov. 2016; soil samples collected from around the roots of forest plants (unidentified); slides reference number AMU/ZD/NC/ Tylencholaimus ibericus /3–4 .

Description

Female

Slender nematodes of small size, slightly curved ventrad upon fixation; body cylindrical, tapering gradually towards both extremities. Cuticle with two distinct layers, 1.5–2.0 μm thick at midbody and 2.0–2.5 μm on tail. Outer cuticle finely striated; inner layer thick, loose, its outline irregular with distinct radial refractive elements. Lateral chords occupying about 23–28% of midbody diameter. Lateral, dorsal and ventral body pores indistinct. Lip region cap-like, offset by constriction, 1.9–2.3 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. Amphids cup-shaped, their aperture occupying about ⅓ to 2/5 of lip region diameter. Stoma a truncate cone. Odontostyle 0.7–0.9 times the lip region diameter long, its aperture about ¼ to ⅓ of the odontostyle length. Odontophore rod-like, with minute basal knobs, 1.0–1.1 times the odontostyle length. Guiding ring simple, refractive, at 0.5–0.6 times the lip region diameter from anterior end. Pharynx consisting of a slender, slightly muscular anterior part, expanding gradually into a cylindrical basal bulb, with thick-walled lumen, occupying about 37–39% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 62–66, DN = 65–69, DO–DN = 1.8–2.9, S1N1 = 75–79, S1N2 = 79–81, S2N = 88–91, S2O = 90–92. Nerve ring at 37–42% of neck length from anterior region. Cardia rounded to conoid, about ¼ to 2/5 of the corresponding body diameter long.

Genital system monodelphic-prodelphic. Ovary reflexed, measuring 30–49 μm long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 28–57 μm, consisting of a slender portion and a slightly developed pars dilatata. Oviduct-uterus junction marked with weak sphincter. Uterus short and tubular, measuring 15–31 μm. Posterior genital branch completely absent. Vagina slightly anteriorly directed, 8.5–10μm or about ½ (48–55%) of midbody diameter; pars proximalis vaginae 5.0–6.5 × 2.5–3.5 μm, encircled by circular muscles; pars distalis vaginae 3.0–3.5 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 3.3–4.9 and rectum 0.8–1.1 times the anal body diameter long. Tail short, rounded to conoid, 1.0–1.5 times the anal body diameter long, with a pair of subdorsal and a prominent terminal caudal pore.

Male

General morphology similar to that of female, except for posterior region being more ventrally curved. Genital system diorchic, testes opposed, sperm cell spindle-shaped. In addition to the adcloacal pair at 6.0 µm from cloacal aperture, there are three ventromedian supplements, located outside the range of spicules, first one at 12 μm from adcloacal pair, second at 16 μm from first and third one at 18 μm from second ventromedian supplement. Spicules typically dorylaimoid, curved ventrad, relatively slender, 5.7 times as long as wide and 1.4 times cloacal body diameter long, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 140°, head occupying about 25% of total spicules length, median piece 10.6 times as long as wide, occupying about 42% of the spicules maximum width, reaching the spicules tip, posterior end 2.5 μm wide. Lateral guiding piece distinct, rod-like, about 5.0 times as long as wide or about 1/5 of the spicules length. Prerectum 5.7 and rectum 1.5 times the cloacal body diameter long. Tail short, rounded to conoid, 0.93 times the cloacal body diameter long, with a pair of caudal pores on each side.

Remarks

Peña-Santiago & Coomans (1994c) described Tylencholaimus ibericus from Spain. Dhanam & Jairajpuri (1999) reported this species from Karnataka, India. Ahmad & Araki (2003) described Tylencholaimus japonicus from Japan, which was considered a synonym of T. ibericus by Peña-Santiago (2008). Later, Li et al. (2008) and Ahad & Ahmad (2016) reported it from China. Wu et al. (2019) described Tylencholaimus zhongshanensis from Zhongshan, China. Recently, Peña-Santiago (2020) synonymized this species with T. ibericus that was accepted herein as well. The morphometrics of the present populations conform well with the type population except in having distinct radial refractive elements (vs indistinct); slightly shorter odontophore (5.5–6.5 vs 6.0–8.0 μm) and presence of male (vs male absent). The present populations conform well with the Indian population described by Dhanam & Jairajpuri (1999) except in having slightly lower b (3.0–3.6 vs 4.0) ratio; shorter tail length (14–18 vs 18–20 μm) and presence of male (vs absent). The morphometrics of the present populations also conform well with the Japanese population described by Ahmad & Araki (2003) except in having lower c (24–33 vs 35–46) and slightly higher c’ (1.0–1.5 vs 0.92–1.1) ratios; shorter prerectum (42–53 vs 70–112 μm) and presence of male (vs absent). The present populations also conform well with earlier as well as recently described Chinese populations by Li et al. (2008), Ahad & Ahmad (2016) and Wu et al. (2019). These differences may be interpreted as geographical or intraspecific variability. Male individuals is reported here for the first time in this species.

Figures

Fig. 5. Tylencholaimus ibericus Peña-Santiago & Coomans, 1994 (LM photographs). A–B. Female anterior region. C. Female anterior region showing amphid. D. Female pharyngeal region. E. Female expanded part of pharynx. F. Female pharyngo-intestinal junction. G. Vulval region. H–I. Female genital system. J. Female posterior region. K. Male posterior region. L. Male posterior end. Scale bars: A–C, E–L = 10 μm; D = 20 μm.