Tylencholaimus ladakhiensis, Ahad, Sumaya & Ahmad, Wasim, 2016

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 : 477-481

Tylencholaimus ladakhiensis sp. n.

( Figs. 15 & 16 )

Measurements: See Table 8.

Description. Female: Slender nematodes of small size, under 1 mm long; body cylindrical, tapering gradually towards both extremities, slightly ventrally curved upon fixation. Cuticle with two distinct layers, 2 Μm thick at midbody and 2.5–3.0 Μm on tail. Outer cuticle thin, finely striated; inner layer thick with distinct radial refractive elements. Lateral chords occupying about 33–38% of the midbody diameter. Lateral, dorsal and ventral body pores indistinct.

Lip region cap-like, offset by slight constriction, 2.3–2.5 times as wide as high or less than one-third of the body diameter at neck base. Lip region truncate, lips amalgamated, with their inner part somewhat elevated; the submedian lips appear as two round bulges (fig 16A). Amphids cup-shaped with aperture located at the level of cephalic constriction and occupying about one-third of lip region diameter. Stoma a truncate cone. Odontostyle 1.0–1.1 times the lip region diameter long, with very narrow but distinct lumen and its aperture more than onefourth of the odontostyle length. Odontophore rod-like with faint basal knobs, 1.0–1.2 times the odontostyle length. Guiding ring simple, refractive, at 0.6 times lip region diameter from anterior end. Pharynx consists of a slender and weakly muscular anterior part, expanding abruptly into a cylindrical basal bulb, with thick-walled lumen, occupying about 38–45% of total neck length. Pharyngeal gland nuclei and their orifices are located as follows: DO = 61–63, DN = 63–66, S1N1 = 76–80, S1N2 = 82–84, S2N = 95–96, S2O = 96–97. Nerve ring located at 38–44% of neck length from anterior end. Cardia rounded, conoid, somewhat less than one-third to one-half of the corresponding body diameter long.

Genital system didelphic-amphidelphic. Ovaries reflexed, measuring 46–55 µm (anterior) and 37–58 µm (posterior) long, not reaching the oviduct-uterus junction; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 54–70 µm (anterior) and 62–82 µm (posterior), its proximal and distal parts not differentiated. Oviduct-uterus junction marked by well developed sphincter. Uterus short and tubular, measuring 20–23 µm (anterior) and 19–20 µm (posterior). Vagina cylindrical; pars proximalis vaginae 4–6 µm long, its wall encircled by muscles; pars distalis vaginae short, with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 2.7–3.4 and rectum 0.7–1.1 anal body diameter long. Tail cylindrical, rounded-conoid, 1.1–1.3 times anal body diameter long, with a distinct terminal caudal pores.

Male: Not found.

Type habitat and locality. Soil around the roots of the Populus sp. near the bank of Suru River, Bulbul Bagh, Kargil, Ladakh, Jammu and Kashmir state, India.

Type specimens. Holotype female on slide Tylencholaimus ladakhiensis sp. n. / 1; paratypes females on slides Tylencholaimus ladakhiensis n. sp. / 2–5; deposited with the nematode collection of the Department of Zoology, Aligarh Muslim University, India.

Etymology. The new species is named after its type locality, Ladakh.

Diagnosis and relationships. Tylencholaimus ladakhiensis sp. n. is characterized by having a small slender body (L = 0.56–0.73 mm, a ratio = 23–36); lip region truncate, set off by a slight constriction; the submedian lips appears as two round bulges; amphid aperture slit-like; odontostyle slender, 7–9 µm long, with comparatively narrow lumen; odontophore 8–9 µm long; pharynx with slender anterior part which expands abruptly into the cylindrical basal bulb, occupying about 38–45% of total neck length; female genital system didelphicamphidelphic and rounded-conoid tail, with distinct terminal caudal pore.

In the nature of its pharyngeal expansion, amphidelphic gonad and tail shape, the new species comes close to T. cosmos Dhanam & Jairajpuri, 1999 and T. cynodonti Nasira, Erum & Shahina, 2005 but differs from the former in its shape of lip region, comparatively slender odontostyle with narrow lumen (vs comparatively robust odontostyle, with wider lumen); amphid aperture one-third of lip region diameter (vs amphidial aperture almost pore-like) and also in the presence of terminal caudal pore (vs terminal caudal pore absent).

From T. cynodonti , the new species differs because of its longer and slender odontostyle with narrow lumen, and the absence of characteristic circle of large cells around vagina which is present in T. cynodonti . The new species further differs from T. cynodonti in having longer prerectum (vs 21–32 µm) and the presence of a terminal caudal pore.

On the basis of body size, pharyngeal expansion and amphidelphic gonad, the new species also comes close to T. savaryi Loof & Jairajpuri, 1968 . However, it differs from it in having lip region offset by a slight constriction (vs offset by a deep constriction); lips rounded and amalgamated (vs lips moderately separated with the inner part elevated and protruding); odontostyle slender, 7–9 µm long, with comparatively narrow lumen (vs odontostyle relatively robust, 5–6 µm, with clear lumen and aperture); vaginal cells absent (vs large cells present in the vaginal region), and tail rounded-conoid (vs convex-conoid).

In all probability, the single specimen of Tylencholaimus described by Ahmad et al. (2009) from Korea, for which no species name was given as the description was based on single specimen, belongs to this new species.

Figures

FIGURE 15. Tylencholaimus ladakhiensis sp. n. 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 16. Tylencholaimus ladakhiensis sp. n. A. & B. Anterior region; C. Anterior end showing amphid; D. Pharyngeal bulb; E. Pharyngo-intestinal junction; F. Female genital system; G. Vulval region; H. Female posterior region. (Scale bar A – C, E, G = 10 µm; D, F, H = 20 µm)

Tables

Table 8. Morphometrics of Tylencholaimus ladakhiensis sp. n. (All measurements in µm)

Characters	Holotype female	Paratype females
n		5
L	692	665±57.2 (567-733)
Body diameter at neck base	20	18.8±1.1 (18-21)
Body diameter at mid body	21	19.6±1.0 (18-21)
Body diameter at anus	15	14.6±1.3 (13-17)
a	32.9	33.9±2.8 (28.3-35.8)
b	4.0	3.8±0.2 (3.5-4.3)
c	40.7	38.3±2.9 (35.4-42.8)
c`	1.1	1.1±0.1 (1.0-1.3)
V	61.4	60±1.3 (57.8-61.3)
G1	12.7	12±1.2 (9.9-13.1)
G2	12.2	13.9±0.4 (13.5-14.6)
Lip region diameter	7.5	7.3±0.2 (7-7.5)
Lip region height	3	3
Amphid aperture	2	2.8±0.2 (2.5-3.0)
Odontostyle length	8	7.8±0.4 (7-8)
Odontophore length	9	8.4±0.4 (8-9)
Guiding ring from anterior end	5	5.0±0.3 (4.5-5.5)
Nerve ring from anterior end	69	68.2±4.4 (63-73)
Neck length	171	170.2±12.2 (157-186)
Expanded part of Pharynx	73	70.8±6.8 (60-79)
Cardia length	9	7±0.7 (6-8)
Anterior genital branch	88	79.7±11.7 (64-92)
Posterior genital branch	85	92.2±9.2 (80-103)
Vaginal depth	8	8.4±0.4 (8-9)
Vulva from anterior end	425	400.2±39.6 (328-436)
Prerectum length	48	43±2.3 (39-45)
Rectum length	16	13.4±2.0 (10-16)
Tail length	17	17.4±1.6 (15-19)