Tylencholaimellus arabicus, Ahmad & Ahad, 2018

Ahmad, Wasim & Ahad, Sumaya, 2018, Description of two new and two known species of the Genus Tylencholaimellus Cobb in M. V. Cobb, 1915 (Nematoda: Dorylaimida: Tylencholaimoidea), Zootaxa 4375 (3), pp. 301-324 : 309-313

Tylencholaimellus arabicus sp. n.

( Figs. 5 & 6 )

Material examined: Twelve females in good state of preservation.

Description. Measurements, see Table 3.

Female: Small sized nematodes, 0.66–0.83 mm long, slightly curved ventrad upon fixation, tapering gradually towards the anterior end. Cuticle with two distinct layers, 4–5 µm thick at midbody and 5–8 µm on tail. Outer cuticle with distinct transverse striations; inner layer thick, with fine transverse striations. Lateral chords occupying about 19–25% of the midbody diameter. Lateral body pores: 3–4 from anterior region to pharynx base, 3–4 between pharynx to vulva and 15–21 between vulva and anus. Two to three ventral body pores and 3 dorsal pores in anterior region.. Lip region offset from body by deep constriction, 2.2–2.4 times as wide as high or about onethird of body diameter at neck base; inner liplets slightly raised. Amphids cup-shaped, their aperture occupying slightly more than one-half of lip region diameter. Stoma a truncate cone. Odontostyle 1.2–1.4 times the lip region diameter long, dorsal accessory piece extending the entire length of the dorsal arm; aperture one-ninth to oneseventh of the odontostyle length. Odontophore with distinct basal knobs, 0.4–0.6 times the odontostyle length. Guiding ring simple, refractive, at 0.7–1.0 times lip region diameter from anterior end. Pharynx consists of a slender and weakly muscular anterior part and a short pear-shaped, constricted basal bulb, occupying 19–24% of total neck length. Pharyngeal glands often visible. Cardia round, hemispheroid, about one-fifth of the corresponding body diameter long. Nerve ring located at 55–65% of neck length from anterior end. Genital system monodelphicopisthodelphic. Ovary reflexed, measuring 74–198 µm long, not reaching the oviduct-uterus junction; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 124–210 µm, proximal and distal parts not differentiated. Oviduct-uterus junction marked by well-developed sphincter. Uterus short, tubular, measuring 29–40 µm. Anterior genital branch reduced to a simple sac, 0.5–1.3 times midbody diameter in length. Vagina cylindrical; pars proximalis vaginae 9–13 µm long, wall encircled by muscles; pars distalis vaginae short, 3–5 µm long with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Sperm present throughout genital tract. Prerectum1.8–2.3 and rectum 0.6–0.8 times anal body diameter in length. Tail short, conoid, 0.6–0.8 anal body diameters long; caudal pores two, one on each side of the tail.

Male: Not found.

Type habitat and locality. Soil around roots of maize plant (Zea mays) from agricultural field, Sabya, Jazan province, Saudi Arabia; 17.1548° N, 42.6269° E.

Type specimens. Holotype female on slide Tylencholaimellus arabicus sp. n. / 1; paratype females on slides Tylencholaimellus arabicus sp. n. / 2–11; deposited with the nematode collection of the Department of Zoology , Aligarh Muslim University, India .

Etymology. The new species is named T. arabicus sp. n. because it is the first Tylencholaimellus species recorded from Arabian Peninsula.

Diagnosis and relationships. Tylencholaimellus arabicus sp. n. is characterized by its small body size (L= 0.66–0.83 mm); outer cuticle with distinct transverse striations; inner layer thick with fine transverse striations; lip region offset by a deep constriction, inner liplets slightly raised; odontostyle 15–17 µm, odontophore 8–10 µm, combined length 25–26 µm; female genital system mono-opisthodelphic; anterior uterine sac 0.5–1.3 times midbody diameter in length; transverse vulva and short conoid tail.

With its offset lip region and slightly raised inner liplets, stylet length and presence of an anterior uterine sac, the new species comes close to T. polonicus Szczygieł, 1962 ; T. pluvialis Siddiqi, 1965 and T. auringiensis Peralta & Peña-Santiago, 1992 . However, it differs, from T. polonicus in having a smaller and more robust body (L= 0.66–0.83 vs 0.85–1.53 mm; a = 28–37 vs 21.8–31.9); lips rounded with indistinct labial and cephalic papillae (vs lips more angular with very distinct labial and cephalic papillae); lip region slightly narrower (11–12 vs 13–15.5 µm); outer cuticle with distinct transverse striations (vs outer cuticle with fine transverse striations); dorsal and ventral pores present (vs dorsal and ventral pores absent); both parts of pharynx separated by a distinct constriction (vs both parts of pharynx separated by a more or less marked depression); comparatively smaller pharyngeal bulb (25–28 vs 31–37 µm); smaller neck length (114–144 vs 147–208 µm); comparatively smaller anterior uterine sac (0.5–1.3 vs 1.3–3.2 body diameters long); comparatively longer rounded-conoid tail (vs tail conoid-rounded, ventrally almost straight, dorsally convex; c = 29–37 vs 37.9–59.7); and male absent (vs present).

From T. pluvialis , the new species differs in having completely rounded, wider lip region, offset by deep constriction (vs truncate lip region, 9–10 µm wide, offset by a comparatively shallow constriction); outer cuticle with distinct transverse striations (vs with fine transverse striations); dorsal and ventral body pores present (vs absent); longer odontostyle (15–17 vs 14.4 µm); wider amphid aperture (7–8 vs 6.4 µm); slightly longer prerectum (55–72 µm vs 40–57 µm) and comparatively more anterior vulva (V = 26.6–30 vs 31–33).

From T. auringiensis , the new species differs in having comparatively smaller and more robust body (L= 0.66–0.83 vs 0.81–1.1 mm; a = 18.5–21.9 vs 23.3–30.7); lip region rounded (vs lip region angular); outer cuticle with distinct transverse striations (vs cuticle apparently smooth); lateral hypodermal glands not present (vs conspicuous glandular bodies present); dorsal and ventral body pore present (vs absent); pharyngeal bulb pearshaped (vs cylindroid); oviduct-uterus junction marked by well developed sphincter (vs oviduct-uterus junction poorly developed); male absent (vs present).

Figures

FIGURE 5. Tylencholaimellus arabicus 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 6. Tylencholaimellus arabicus sp. n. A & B. Anterior region; C. Anterior end showing amphid; D & E. Anterior region showing ventral and dorsal body pore; F. Pharyngeal bulb; G. Female genital system; H & I. Female posterior region and showing caudal pore. (Scale bar A–C, I = 10 µm; D–H = 20 µm)