Tylencholaimus arakii, 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 : 474-477

Tylencholaimus arakii sp. n.

( Figs. 13 & 14 )

Measurements: See Table 7 .

Description. Female: Small sized nematodes, 0.56–0.65 mm long, slightly curved upon fixation; body cylindrical, tapering gradually towards both extremities. Cuticle with two distinct layers, 2 Μm thick at midbody and 3–4 Μm on tail. Outer cuticle finely striated; inner layer thick with distinct radial refractive elements. Lateral chords occupying about 32–38% of the midbody diameter. Lateral body pores present, but their actual number cannot be ascertained because of dust particles attached on the body surface.

Lip region cap-like, offset by a constriction, 1.7–2.3 times as wide as high or about one-fourth to one-third of the body diameter at neck base. Lips rounded and amalgamated, with inner part elevated forming a perioral disc. Amphids cup-shaped with aperture located at the level of cephalic constriction and occupying about one-half of lip region diameter. Stoma a truncate cone. Odontostyle 1.0–1.1 times the lip region diameter long, its aperture about one-seventh to one-fifth of the odontostyle length. Odontophore 0.8–1.1 times the odontostyle length with asymmetrical basal knobs, lobe of the ventral arm always bigger than the dorsal one. Guiding ring simple, refractive, at 0.5–0.8 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 45–47% of the total neck length. Pharyngeal gland nuclei and their orifice are located as follows: DO = 56–57, DN = 59–60, S1N1 = 70–76, S1N2 = 72–78, S2N = 89–90, S2O = 89–90. Nerve ring located at 27–35% of neck length from anterior end. Cardia hemispherical, about one-fourth to one-third of the corresponding body diameter long.

Genital system monoprodelphic. Ovary reflexed, measuring 57–91 µm long, not reaching the oviduct-uterus junction; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 72–81 µm, its proximal and distal parts not differentiated; oviduct-uterus junction marked by weak sphincter. Uterus short and tubular, measuring 30–34 µm. Posterior genital branch completely absent. Vagina cylindrical; pars proximalis vaginae 7–8 µm long, its wall encircled by muscles; pars distalis vaginae short, 1.5–2.0 µm long with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 2.8–4.0 and rectum 0.6–0.8 anal body diameter long. Tail short, hemispheroid, 1.0–1.1 times anal body diameter long, with two caudal pores on each side, terminal caudal pore prominent.

Male: Not found.

Type habitat and locality. Soil around the roots of grasses (unidentified) from Koibuchimachi, Mito C., Ibaraki, Japan. Collected by Dr. M. Araki on December 2011.

Type specimens. Holotype female on slide Tylencholaimus arakii sp. n. / 1; paratypes females on slides Tylenchoalimus arakii 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 Dr. Masaki Araki of the National Institute for Agro- Environmental Sciences, Tsukuba, Japan in recognition of his contribution to Nematology in Japan.

Diagnosis and relationships. Tylencholaimus arakii sp. n. is characterized by having 0.56–0.65 mm long body; labial disc present; lip region cap-like, set off by a shallow constriction; odontostyle 7–8 µm long; odontophore 7–8 µm long, with well developed asymmetrical basal knobs; total stylet length 15 Μm; pharynx with slender anterior part which expands abruptly into the cylindrical basal bulb occupying about 45–47% of total neck length; female genital system monoprodelphic; transverse vulva and short, hemispheroid tail.

In the presence of characteristically enlarged asymmetrical basal knobs of the odontophore, the new species comes close to T. confusus Ahmad & Araki, 2003 and T. porosus Vinciguerra & Zullini, 1980 .

From T. confusus , it differs in having smaller body size (vs L = 0.8–0.9 mm); lip region with perioral labial disc (vs lip region without labial disc); lower a (vs a = 29–33), b (vs b = 3.8–4.4) and c’ ratios (vs c `=1.3–1.4); shorter odontophore (vs 11–11.5 µm); slightly posterior vulva (vs V=61–65); posterior genital branch completely absent (vs 8–10 µm long posterior uterine sac present); shorter prerectum (vs 100–153 µm) and smaller and differently shaped tail (vs tail conoid, 25–28 µm long).

From T. porosus , the new species distinctly differs in having smaller body size (vs L= 0.7–1.1 mm); in the presence of labial disc (vs absence); comparatively longer odontostyle (vs 6 µm); odontophore with enlarged asymmetrical basal knobs (vs odontophore with large globe-shaped basal knobs); posterior genital branch completely absent (vs post-vulval branch 5 times the corresponding body diameter long); posterior vulva position (vs V = 55–56), and shorter tail (vs 25 µm long, c = 25.7–32.6 vs 37.2).

T. vigil Andrássy, 1959 also has comparatively strong odontophore knobs but it distinctly differs from the new species in the shape of its lip region which is sharply offset and without labial disc.

In the presence of a slightly offset lip region, perioral region with labial disc, abruptly enlarging pharyngeal expansion, absence of post-vulval uterine sac and short rounded tail, the new species also comes close to T. minimus de Man, 1876 and T. minutus Vinciguerra, 1986 . However, it differs from T. minimus in having a slightly longer odontostyle (7–8 µm vs 5.5–6 µm); odontophore with enlarged asymmetrical basal knobs (vs odontophore with symmetrical small basal knobs); lower b value (2.8–3.1 vs 3.4–3.9); and longer pharynx (192–204 vs 152–169 µm) and pharyngeal bulb (88–96 vs 63–72 µm).

From T. minutus , the new species differs in having longer odontostyle (7–8 µm vs 4–5 µm); odontophore with enlarged asymmeterical basal knobs (vs odontophore with small basal knobs); longer pharynx (192–204 vs 121–161 µm); larger basal bulb (88–9 vs 46–68.5 µm); in having hemispheroid tail (vs tail conical, somewhat digitate) and lower c’ value (1.0–1.1 vs 1.3–1.9).

Figures

FIGURE 13. Tylencholaimus arakii sp. n. A. Entire female; B. Anterior region; C. Odontostyle and odontophore; D. Anterior end; E. Pharyngeal region; F. Pharyngeal bulb; G. Female genital system; H. Female posterior region.

FIGURE 14. Tylencholaimus arakii sp. n. A. & B. Anterior region; C. Anterior end showing amphid; D. Pharyngeal bulb; E. Pharyngeal expansion F. Pharyngo-intestinal junction; G. Female genital system; H. Vulval region; I. Female posterior region. (Scale bar A – C, E, F, H = 10 µm; D, G, I = 20 µm)

Tables

Table 7. Morphometrics of Tylencholaimus arakii sp. n. (All measurements in µm)

Characters	Holotype female	Paratype females
n		4
L	625	576±11.8 (565-595)
Body diameter at neck base	26	25.7 ± 0.4 (25-26)
Body diameter at mid body	26	25.5±0.5 (25-2 6)
Body diameter at anus	19	19.7±0.8 (19-21)
a	25.07	22.5±0.4 (21.7-23)
b	3.1	2.9±0.08 (2.8-3)
c	32.6	27.07±0.9 (25.7-28.2)
c`	1.0	1.05±0.05 (1.0-1.1)
V	66.4	68.3±0.57 (67.5-69.1)
G1 Lip region diameter	17.7 7	17.2±0.7 (16.6-18.4) 6.7±0.4 (6-7)
Lip region height	3	3.25±0.4 (3-4)
Amphid aperture	3.5	3.6±0.4 (3-4)
Odontostyle length	7	7.5±0.5 (7-8)
Odontophore length	8	7.5±0.5 (7-8)
Guiding ring from anterior end	4	4.5±0.5 (4-5)
Nerve ring from anterior end	69	63.7±6.7 (52-68)
Neck length	204	193.5±1.5 (192-196)
Expanded part of Pharynx	96	89.7±1.2 (88-91)
Cardia length	10	7.2±0.4 (7-8)
Anterior genital branch	116	99.5±3.2 (95-104)
Vaginal depth	12	11.7±0.4 (11-12)
Vulva from anterior end	433	393.7±5.4 (387-402)
Prerectum length	77	62.5±6.1 (55-69)
Rectum length	16	14.2±0.8 (13-15)
Tail length	20	21.2±0.8 (20-22)