Tylencholaimus macroamphidius, 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 : 76-81

Tylencholaimus macroamphidius sp. nov.

urn:lsid:zoobank.org:act:10F3DAD5-CF89-4677-95FA-A06D29395E95

Figs 7–8 , Table 6

Diagnosis

Tylencholaimus macroamphidius sp. nov. is characterized by having 0.6–0.8 mm long, slender body; lip region set off by deep constriction, lips separate, angular; amphids large; odontostyle 8.0–9.0 μm, odontophore 8.5–9.5 μm with asymmetrical basal knobs, total stylet length 17.0–18.5 μm; pharynx with weakly muscular anterior part expanding gradually into a cylindrical basal bulb occupying about 38–43% of total neck length; female genital system monodelphic-prodelphic; posterior branch 39– 70 μm or 2.0–3.5 times the midbody diameter long, consisting of uterus, sphincter, and with a saclike structure representing a rudimentary oviduct; vulva transverse; tail rounded to conoid and males with 19–23 μm long spicules, lateral guiding pieces 5.0–6.0 μm long and three spaced ventromedian supplements.

Etymology

The new species is named Tylencholaimus macroamphidius sp. nov. because of its characteristically large amphids.

Material examined

Holotype INDIA • 1 ♀; Tamil Nadu State, Nilgiris Hill, Naduvattum ; 11º28′37.8″ N, 76º32′36.7″ E; 5–15 cm depth; 15 Nov. 2016; roots of shrubs (unidentified); slide reference number AMU/ZD/NC/ Tylencholaimus macroamphidius /1.

Paratypes INDIA • 4 ♀♀, 2 ♂♂; same collection data as for holotype; slides reference number AMU/ZD/NC/ Tylencholaimus macroamphidius /2–5 • 1 ♀, 2 ♂♂; same collection data as for holotype; slides reference number AMU/ZD/NC/ Tylencholaimus macroamphidius /6–8; nematode collection of the Zoological Survey of India, Kolkata, India .

Type habitat and locality

Soil samples collected from around the roots of shrubs (unidentified) from Naduvattum, Nilgiri Hills, Tamil Nadu State.

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, 1.5– 2.0 μm thick at midbody and 2 μm on tail. Outer cuticle thin, finely striated; inner layer thick, its outline somewhat irregular, with distinct radial refractive elements, more distinct in caudal region. Lateral chords occupying about 25–29% of midbody diameter. Lateral, dorsal and ventral body pores indistinct. Lip region cap-like, offset by deep constriction, 2.0–2.5 times as wide as high or about ½ to 2/5 of the body diameter at neck base. Lips moderately separate, angular, inner part slightly elevated and protruding. Labial and cephalic papillae distinct but not interfering with the labial contour. Amphids large, stirrup-shaped, their aperture occupying about ½ to 3/5 of lip region diameter. Stoma a truncate cone. Odontostyle 0.8–1.0 times the lip region diameter long, its aperture about ⅓ of the odontostyle length. Odontophore 1.0–1.1 times of the odontostyle length with asymmetrical basal knobs, the subventral knobs always larger than dorsal one. Guiding ring simple, refractive, at 0.6–0.9 times the lip region diameter from anterior end. Pharynx consisting of a slender, slightly muscular anterior part, expanding gradually into a cylindroid basal bulb, with thick-walled lumen, occupying about 38–43% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 61–64, DN = 63–67, DO–DN = 1.5–3.1, S1N1 = 73–76, S1N2 = 77–81, S2N = 88–90, S2O = 90–91. Nerve ring at 33–39% of neck length from anterior region. Cardia rounded to conoid, about ⅓ to 3/5 of the corresponding body diameter long.

Genital system monodelphic-prodelphic. Ovary reflexed, measuring 24–49 μm long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 49–84 μm, consisting of a slender distal part and a well developed pars dilatata. Oviduct-uterus junction marked with welldeveloped sphincter. Uterus short, tubular, measuring 33–45 μm. Posterior genital branch 39–70 μm or 2.0–3.5 times the midbody diameter long, comprised of uterine part measuring 29–54 μm and distinct sphincter followed by sac-like structure representing rudimentary oviduct. Sperm cell present throughout the genital tract. Vagina cylindrical, extending inwards, 8.5–10.5 μm or about 2/5 to ½ (43–53%) of midbody diameter; pars proximalis vaginae 6.5–7.0 × 2.0–2.5 μm, encircled by circular muscles; pars distalis vaginae 3.0–3.5 μm with slightly curved walls; pars refringens absent. Vulva a transverse slit. Prerectum 2.6–4.0 and rectum 0.9–1.0 times anal body diameter long. Tail short, conoid, ventrally curved with rounded terminus, 1.4–1.6 times anal body diameter long, with a pair of subdorsal caudal pores.

Male

General morphology similar to that of female, except for the posterior body region being comparatively more ventrally curved. Genital system diorchic, testes opposed, sperm cell spindle-shaped. In addition to adcloacal pair at 3.0–5.0 μm from cloacal aperture, there are three ventromedian supplements, located outside the range of spicules, first one at 16–20 μm from adcloacal pair, second at 8.0–10 μm from first, and third at 8.0–14 μm from second ventromedian supplement. Spicules typically dorylaimoid, curved ventrad, relatively robust, 4.9–5.8 times as long as wide, 1.0–1.4 times as long as cloacal body diameter, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 120–123º, head occupying about 14–17% of total spicules length, median pieces 11.3–12.5 times as long as wide, occupying about 37% of the spicules maximum width, reaching the spicules tip, posterior end 2.0–2.5 μm wide. Lateral guiding pieces slender, about 4.0–6.0 times as long as wide or about ⅓ of total spicules length. Prerectum 4.2–5.0 and rectum 1.0–1.2 cloacal body diameter long. Tail short, conoid, 1.1–1.2 times cloacal body diameter long with a pair of subdorsal caudal pores.

Taxonomic remarks

In the presence of asymmetrical basal knobs of the odontophore, the new species comes close to T. confusus Ahmad & Araki, 2003 and T. arakii Ahad & Ahmad, 2016 , but differs from the former in having longer odontostyle (8.0–9.0 vs 6.5–7.5 μm); pharyngeal expansion gradual (vs abrupt); slightly shorter pharyngeal expansion (73–82 vs 83–93 μm); slightly posterior vulva position (V = 65.7–68.5 vs 61–65); longer posterior genital branch with distinct sphincter and rudimentary oviduct (39–60 vs 8.0– 10 μm, sphincter and rudimentary oviduct absent) and fewer ventromedian supplements (3 vs 4–6).

The new species differs from T. arakii in having differently shaped (lips moderately separate and angular vs lips rounded and amalgamated) and wider lip region (9.0–10.0 vs 6.0–7.0 μm); wider amphidial aperture (4.5–5.5 vs 3.0–4.0 µm); absence of labial disc (vs present); higher b (3.4–4.3 vs 2.8–3.1) and c’ (1.4–1.6 vs 1.0–1.1) ratios; shorter pharyngeal expansion (73–82 vs 88–96 μm) and presence of posterior sac (vs absent).

In the presence of gradual pharyngeal expansion and long posterior sac, the new species comes close to T. stecki Steiner, 1914 and T. vulvulatus Rahman et al., 1987 . However, it differs from T. stecki , in having wider amphidial aperture (4.5–5.5 vs 3.0–3.5 µm); longer odontostyle (8.0–9.0 vs 5.0–5.5 μm), odontophore with asymmetrical basal knobs (vs symmetrical); slightly shorter pharynx and its expansion (170–196 vs 203–236 μm, 73–82 vs 89–102 μm); lower c (28–37 vs 44–59) and higher c’ (1.4–1.6 vs 0.7–0.9) ratios.

The new species differs from T. vulvulatus in having a longer odontostyle (8.0–9.0 vs 6.0–7.0 μm), odontophore with asymmetrical basal knobs (vs symmetrical); vulval lips symmetrical (vs asymmetrical); lower c (28–37 vs 40–61), higher c’ (1.4–1.6 vs 0.7–1.0) ratios and smaller spicules (19–23 vs 28–32 μm).

In the presence of gradual pharyngeal expansion and long posterior sac the new species also comes close to T. australis Yeates, 1979 but differs in having longer body (0.61–0.85 vs 0.50–0.54 mm); wider amphidial aperture (4.5–5.5 vs 2.0–2.5 µm); longer odontostyle (8.0–9.0 vs 4.5–5.0 µm) and odontophore (9.0–9.5 vs 5.0 µm); knobs of odontophore asymmetrical (vs symmetrical); longer posterior genital branch with distinct sphincter and rudimentary oviduct (39–70 vs 25 µm, sphincter and rudimentary oviduct absent) and presence of male (vs absent).

Figures

Fig. 7. Tylencholaimus macroamphidius sp. nov.A, C, F–G. Holotype, ♀ (AMU/ZD/NC/Tylencholaimus macroamphidius/1). B, D, H–J. Paratype 6, ♂ (slide 5). E. Paratype 3, ♀ (slide 3). A. Entire female. B. Entire male. C. Female anterior region. D. Male anterior region showing amphid. E. Female expanded part of pharynx. F. Female genital system. G. Female posterior region. H. Male posterior region. I. Spicule. J. Lateral guiding piece.

Fig. 8. Tylencholaimus macroamphidius sp. nov. (LM photographs). A–B, F, G, I. Holotype, ♀ (AMU/ ZD/NC/Tylencholaimus macroamphidius/1). C. Paratype 6, ♂ (slide 5). D–E. Paratype 2, ♀ (slide 3). H. Paratype 1, ♀ (slide 2). J. Paratype 7, ♂ (slide 6). K. Paratype 9, ♂ (slide 8). A–B. Female anterior region. C. Male anterior region showing amphid. D. Female pharyngeal region. E. Female expanded part of pharynx. F–H. Female genital system. I. Female posterior region. J. Male posterior region. K. Male posterior end showing spicules. Scale bars: A–C, E, G–K = 10 μm; D, F = 20 μm.