Tylencholaimellus montanus Thorne, 1939

Zhang, Min, Ahad, Sumaya, Liang, Wenju & Ahmad, Wasim, 2012, A new and three known species of the genus Tylencholaimellus Cobb in M. V. Cobb, 1915 (Nematoda: Dorylaimida) from Changbai Mountain, China, Zootaxa 3499, pp. 46-62 : 54-58

Tylencholaimellus montanus Thorne, 1939

( Figs. 5 , 6 )

Measurements: Table 3.

Description. Female: Moderately slender nematodes of small size. Body cylindrical, curved ventrad upon fixation, slightly tapering towards both extremities. Cuticle with two distinct layers, 2.0–2.5 µm thick at mid body and 3 µm on tail. Outer cuticle with fine transverse striations; inner cuticle distinctly striated; radial refractive elements abundant. Lateral, dorsal and ventral body pores indistinct. Lateral chords occupying about one-fifth of mid body diameter. Lip region slightly offset by a weak constriction, 1.5–2.0 times as wide as high and one-third of the body diameter at neck base. Lips amalgamated, with rounded contour; its inner portions transformed into a perioral disc. Amphid cup-shaped, opening at level of the cephalic constriction and occupying about two-thirds of the lip region diameter. Stoma a truncate cone. Odontostyle 1.2–1.5 times the lip region width long and provided with dorsal accessory piece covering the entire dorsal arm; its aperture one-fifth of the odontostyle length. Odontophore with basal knobs; 0.7–0.8 times the odontostyle length. Guiding ring simple, refractive, at 0.7–0.9 times lip region width from anterior end. Pharynx consists of a slender and weakly muscular anterior part separated from a cylindrical basal bulb by a depression, which occupies about 18.6–23.8% of the total neck length. Pharyngeal gland often visible. Cardia hemispherical, partially surrounded by the intestine. Nerve ring at 48–61% of the neck length. Genital system monodelphic-opithodelphic. Ovary reflexed, measuring 40–90 µm long; oocytes arranged in single row except near its tip. Oviduct joining the ovary subterminally, measuring 53–88 µm and consisting of a slender distal part and a poorly developed pars dilatata. Weakly developed sphincter present at oviduct-uterus junction. Uterus short and tubular, measuring 25–37 µm; sperms not present in either uterus or oviduct. Anterior genital branch practically vestigial, almost always appearing as a small cell mass with inconspicuous lumen. Vagina cylindrical, pars proximalis vaginae 9–10 µm long, its wall encircled by muscles. Pars distalis vaginae short, 0.5–1.0 µm long with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 3.4–4.7 times anal body diameter long. Intestine-prerectum junction guarded by three cells. Rectum 0.9–1.2 anal body diameter long. Tail cylindroid and relatively long; outer layer of cuticle thickened posteriorly forming a distinct hyaline layer.

Male: Not found.

Habitat and locality: Mixed coniferous broad-leaved forest, Changbai Mountain, Northeast China (42°24ʹN, 128°06ʹE): 760m a.s.l., annual mean temperature 2.6 ºC, annual mean precipitation 691 mm; tree species were dominated by a mixture of coniferous Pinus koraiensis , broadleaved Quercus spp. and Acer spp. on Albi-Boric Argosols.

Mean ± SD (Range)

n 7

L (mm) 645±47.5(593–755) Body width at neck base 22±0.5 (21–23) Body width at mid body 23.8±0.6 (23–25) Body width at anus 15±0.7 (14–16) a 26.7±2.7 (24–33) b 4.6±0.4 (4.0–5.2) c 26.6±1.5 (25–30) c`1.5±0.04 (1.5–1.6) V 35.8±2.0 (33–39) G1 1.66±0.12 (1.5–1.9) G2 15.4±1.8 (13–18) Lip region width 6.57±0.31 (6–7) Lip region height 3.8±0.2 (3.5–4.0) Amphid aperture 3.8±0.2 (3.5–4.0) Odontostyle length 9±0

Odontophore length 7. 14±0.34 (7–8) Guiding ring from anterior end 5.14±0.34 (5–6) Nerve ring from anterior end 75.8±5.2 (69–83) Neck length 139±5.7 (132–147) Expanded part of pharynx 30±2.5 (25–33) Cardia length 4.3±0.45 (4–5)

Anterior genital branch 10.8±0.9 (9–12) Posterior genital branch 99±10.5 (83–114) Vaginal depth 13±0.92 (12–14) Vulva from anterior end 231±16.5 (210–257) Prerectum length 58.7±4.65 (51–66) Rectum length 17.3±1.6 (15–20) Tail length 24±0.9 (22.5–25) Remarks: Thorne (1939) described this species from Utah and differentiated it from the closely related species, T. striatus Thorne, 1939 mainly in having somewhat more slender body, less strongly striated subcuticle and a more conoid rather than hemispheroid tail. Andrássy (1967) identified a single female specimen of this species from Argentina which had a comparatively longer tail (2 anal body widths). Goseco et al. (1975) in their revision of the genus Tylencholaimellus examined the type specimens, redescribed this species and also designated a lectotype and paralectotype. In their description, the tail shape of the female is conoid (Figs. 10EF of Goseco et al., 1975), the a ratio is 27–30 and they also mentioned the presence of body pores. Peralta & Peña-Santiago (1995) recorded three populations of T. montanus from Spain. Their specimens had a values ranging from 19–28 and rounded-conoid to cylindroid tails, mostly dorsally convex but sometimes ventrally almost straight. They redescribed T. striatus also in the same paper and differentiated the two species mainly in the shape of lip region, being scarcely offset in T. montanus , but more strongly offset in T. striatus , which also has a cylindroid tail with a thick hyaline outer layer in the terminal portion. Mushtaq, Naz & Ahmad (2007) also mentioned a thick terminal tail cuticle in T. striatus . The present Chinese specimens conform well to the earlier descriptions in their morphometrics. The lip region is offset by a depression rather than constriction and the tail shape is more like Spanish populations, and quite different from the original American specimens. In our specimens the prerectum is also slightly longer (vs 31–56 µm or 2–3 anal body widths long). These differences could be due to geographical variation.

The two species, T. striatus and T. montanus are morphometrically very similar to each other but still display some definite morphological differences which clearly differentiate these two species. These include: the shape of lip region, being scarcely offset in T. montanus (vs strongly offset), distinctly striated subcuticle (vs strongly striated subcuticle, the striation being more pronounced in pharyngeal region), and tail shape. The amphids are comparatively wide in T. montanus , almost occupying the entire lateral surface at that level (vs about two-thirds lip region width in T. striatus ).

Figures

FIGURE 5. Tylencholaimellus montanus Thorne, 1939. A: Entire female. B: Anterior region. C: Anterior end showing amphid. D: Pharyngeal region. E: Expanded part of pharynx. F: Female genital system. G: Female posterior region.

FIGURE 6. Tylencholaimellus montanus Thorne, 1939. A: Anterior region. B: Anterior end showing amphid. C: Expanded part of pharynx. D: Female genital system. E – F: Female posterior region (scale bar: 20 µm).