Tylencholaimus southindicus, 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 : 87-92

Tylencholaimus southindicus sp. nov.

urn:lsid:zoobank.org:act:995DAB2D-59D1-4B2D-BD2E-07B06E46C5A5

Figs 11–12 , Table 8

Diagnosis

Tylencholaimus southindicus sp. nov. is characterized by having 0.44–0.55 mm long, slender body; lip region offset by constriction, labial disc distinct; odontostyle 4.5–5.5 μm, odontophore 5.0–6.0 μm, total stylet length 10–11.5 μm; pharynx with slender anterior part expanding abruptly into a cylindrical basal bulb occupying about 39–43% of total neck length; female genital system monodelphic-prodelphic; posterior genital branch reduced to a simple sac, 22–54 μm or 1.2–3.0 times the midbody diameter long; vulva transverse; tail short, rounded to rounded-conoid; males with 17–18 µm long spicules, 4.5–5.5 µm long lateral guiding pieces and two spaced ventromedian supplements.

Etymology

The new species is named Tylencholaimus southindicus sp. nov. because of its distribution in south India.

Material examined

Holotype INDIA • 1 ♀; Kerala State, Ernakulam district, Manikandanchal ; 10º09′28.8″ N, 76º47′56.4″ E; 5–15 cm depth; 28 Oct. 2017; roots of shrubs (unidentified); slide reference number AMU/ZD/NC/ Tylencholaimus southindicus /1.

Paratypes INDIA • 9 ♀♀, 7 ♂♂; same collection data as for holotype; slides reference number AMU/ZD/NC/ Tylencholaimus southindicus /2–5 • 1 ♀, 1 ♂; same collection data as for holotype; slide reference number AMU/ZD/NC/ Tylencholaimus southindicus /6, nematode collection of the Zoological Survey of India, Kolkata, India .

Other material

INDIA • 16 ♀♀; Karnataka State, Kodagu district, Bhagamandala ; 12º23′29.1″ N, 75º31′50.0″ E; 5–15 cm depth; 8 Nov. 2016; roots of shrubs and forest trees (unidentified); slides reference number AMU/ZD/NC/ Tylencholaimus southindicus /7–13 .

Type habitat and locality

Soil samples collected from around the roots of shrubs (unidentified) from Manikandanchal, Ernakulam district, Kerala State.

Other habitat and locality

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

Description

Female

Small sized nematodes, 0.44–0.55 mm long; curved ventrad 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 1.5–2 μm on tail. Outer cuticle finely striated; inner layer thick, with radial refractive elements. Lateral chords occupying about 23–31% of midbody diameter. Lateral, dorsal and ventral body pores indistinct. Lip region cap-like, offset by distinct constriction, 1.4–2.0 times as wide as high or about ⅓ of the body diameter at neck base. Lips rounded, amalgamated, inner part elevated, transformed into a labial disc-like structure. Amphids small, cup-shaped, their aperture occupying about ⅓ to 2/5 of lip region diameter. Stoma a truncate cone. Odontostyle short, slender, anterior end slightly thick, 0.8–1.0 times the lip region diameter long, its aperture about 1/5 to ⅓ of the odontostyle length. Odontophore rod-like, with minute basal knobs, 1.0–1.2 times the odontostyle length. Guiding ring simple, refractive, at 0.6–0.8 times 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 39–43% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 62–65, DN = 65–68, DN–DO = 1.9–3.4, S1N1 = 75–79, S1N2 = 79–82, S2N = 88–90, S2O = 90–92. Nerve ring located at 36–43% of neck length from anterior region. Cardia rounded to conoid, about ⅓ of the corresponding body diameter long.

Genital system monodelphic-prodelphic. Ovary reflexed, measuring 32–86 μm long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 53–102 μm, with a welldeveloped pars dilatata. Oviduct-uterus junction marked by well-developed sphincter. Uterus slightly long and tubular, measuring 27–53 μm. Posterior genital branch reduced to simple sac, measuring 22–54 μm or 1.2–3.0 times midbody diameter. Sperm cell present throughout the genital tract. Vagina cylindrical, extending inwards, 8.0–10 μm or about ½ to 3/5 (46–61%) of midbody diameter; pars proximalis vaginae 5.0–7.0 × 3.0–5.0 μm, encircled by circular muscles; pars distalis vaginae short, 2.0–3.0 μm with slightly curved walls; pars refringens absent. Vulva a transverse slit. Prerectum 3.4–6.6 and rectum 0.9–1.2 times anal body diameter long. Tail short, rounded to rounded-conoid, 0.6–0.9 times anal body diameter long, with a pair of subdorsal and a prominent terminal caudal pore present.

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 adcloacal pair at 4.0–5.0 µm from cloacal aperture, there are two ventromedian supplements, located outside the range of spicules, first one at 22–31 μm from adcloacal pair, second at 16–31 μm from first ventromedian supplement. Spicules typically dorylaimoid, curved ventrad, 4.3–5.1 times as long as wide and 1.3–1.5 times as long as body diameter at level of cloacal aperture, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 125–130º, head occupying about 10–11% of total spicules length, median pieces 7.5–11.3 times as long as wide, occupying about 37– 57% of the spicules maximum width, reaching the spicules tip, posterior end 1.5–2.0 μm wide. Lateral guiding pieces distinct, rod-like, about 3.3–5.0 times as long as wide or about ¼ to ⅓ of the spicules length. Prerectum 5.1–7.9 and rectum 1.5–1.7 times cloacal body diameter long. Tail short, rounded to conoid, 0.7–1.0 times cloacal body diameter long; a pair of subdorsal and a prominent terminal caudal pore present.

Taxonomic remarks

In the presence of labial disc, abrupt pharyngeal expansion, presence of posterior uterine sac and short rounded to hemispheroid tail, the new species comes close to T. imperamus Mohilal & Dhanachand, 2003 ; T. discus Golhasan et al., 2019 and T. constrictus Vinciguerra, 1986 but differs from the former in the shape and size of labial disc (large vs small); distinctly offset lip region (vs lip region almost continuous); longer post-uterine sac (22–54 vs 9.0–18 μm); smaller spicules (17–18 vs 24–25 μm) and fewer ventromedian supplements (2 vs 3).

The new species differs from T. discus in having a shorter body size (0.44–0.55 vs 0.65–0.76 mm); comparatively smaller amphidial aperture (2.0–2.5 vs 3.0–4.0 μm); shorter total stylet length (10.0– 11.5 vs 15.0–17.5 μm, odontostyle 4.5–5.5 vs 6.0–7.0 μm, odontophore 5.0–6.0 vs 9.0–10.5 μm); odontophore with minute basal knobs (vs large knobs); shorter pharynx and its expansion (142–164 vs

230–259 μm, 56–71 vs 98–125 μm); slightly shorter tail length (9.0–11 vs 13–17 μm) and presence of male (vs absent).

The new species differs from T. constrictus in having a shorter body size (0.44–0.55 vs 0.76–0.96 mm); narrower lip region (5.0–6.0 vs 7.0–8.0 μm); smaller amphidial aperture (2.0–2.5 vs 4 μm), shorter odontophore (5.0–6.0 vs 9.0–10 μm); longer post-uterine sac (22–54 vs 5.0–16 μm); shorter spicules (17–18 vs 28 μm) and fewer ventromedian supplements (2 vs 5–6).

In the presence of long posterior uterine sac, the new species also comes close to T. longicaudatus Peña- Santiago & Coomans, 1994 and T. conicaudatus Peña-Santiago & Coomans, 1994 but differs from the former in having a shorter body size (0.44–0.55 vs 0.60–0.77 mm); comparatively posterior vulva position (V = 64–70 vs 59–63); shorter post-uterine sac (22–54 vs 61–90 μm) and shorter tail (9.0–11 vs 31–41 μm, c = 39–64 vs 18–21, c’ = 0.6–1.0 vs 2.1–3.2).

The new species differs from T. conicaudatus in having a slightly narrow lip region (5.0–6.0 vs 7.0– 8.0 μm); pharyngeal expansion abrupt (vs gradual); slightly posterior vulva position (V = 64–70 vs 61–65); higher c (39–62 vs 21–24) and lower c’ (0.6–1.0 vs 1.3–1.6) ratios; tail rounded (vs conoid) and presence of male (vs absent).

Figures

Fig. 11. Tylencholaimus southindicus sp. nov. A. Paratype 1, ♀ (slide 2). B, J–L. Paratype 11, ♂ (slide 5).C, E. Paratype 5, ♀ (slide 3). D, I. Holotype, ♀ (AMU/ZD/NC/Tylencholaimus southindicus/1). F. Paratype 3, ♀ (slide 2). G. Paratype 4, ♀ (slide 2). H. Paratype 13, ♀ (slide 5). A. Entire female. B. Entire male. C. Female anterior region. D. Female anterior region showing amphid. E. Female pharyngeal region. F. Female expanded part of pharynx. G–H. Female genital system. I. Female posterior region. J. Male posterior region. K. Spicule. L. Lateral guiding piece.

Fig. 12. Tylencholaimus southindicus sp. nov. (LM photographs). A. Paratype 1, ♀ (slide 2). B, E, G. Holotype, ♀ (AMU/ZD/NC/Tylencholaimus southindicus/1). C–D, F. Paratype 5, ♀ (slide 3). H–J. Paratype 4, ♀ (slide 2). K–L. Paratype 3, ♂ (slide 2). A–B. Female anterior region. C. Female anterior region showing amphid. D. Female pharyngeal region. E. Female expanded part of pharynx. F. Female pharyngeal expansion. G. Female pharyngo-intestinal junction. H–I. Female genital system. J. Female posterior region. K. Male posterior region. L. Male posterior end showing spicules. Scale bars: A–C, E–L = 10 μm; D = 20 μm.