Tylencholaimus parvus Ahmad and Araki, 2003

Ahmad, Wasim, Park, Byeong-Yong, Lee, Jae-Kook & Choi, Dong-Ro, 2009, Some new and known species of Tylencholaimoidea (Nematoda: Dorylaimida) from Korea, Journal of Natural History 43 (37 - 38), pp. 2329-2356 : 2335-2338

Tylencholaimus parvus Ahmad and Araki, 2003

( Figure 3A–E ; Table 2)

Description

Female. Lip region cap-like, offset by constriction, about twice as wide as high and about one-third as wide as body width at neck base. Amphids small, cup-shaped with a small slit-like aperture. Odontostyle about 0.7–0.8 times the lip region width long. Guiding ring simple, at 0.60–0.65 times the lip region width from anterior end.

Odontophore rod-like with small basal knobs, 1.0–1.1 times the odontostyle length. Anterior part of pharynx slender and rather muscular, expanding gradually into the basal expanded part; latter occupying 41–45% of total neck length. Cardia short conoid. Genital system monodelphic–prodelphic; posterior genital branch completely absent. Vagina bent forward, about half the corresponding body width deep. Vulva transverse. Tail short hemispheroid, always with a distinct terminal caudal pore.

Male. Not found.

Habitats and localities

Soil around the roots of forest trees from (1) Heugsando, Jeollanam-do; (2) Uleungdo, Gyeongsangbuk-do; (3) Geomoondo, Jeollanam-do; (4) Jincheon, Jincheon-gun, Gyeongi-do; (5) Jungmisan mountain , Yangpeong-gun, Gyeongi-do. All localities in South Korea .

Remarks

Ahmad and Araki (2003) described this species from Japan. This species appears to be widely distributed in forest soils of Korea. The present specimens agree fairly well with the Japanese population except that the Korean specimens have a comparatively smaller expanded part of the pharynx (versus 47–50% in Japanese specimens), slightly posterior vulva (versus V = 69–74.5, mean 71), and slightly longer tail (versus tail 9.5– 12 µm, c′ = 0.55–0.88). Ahmad and Araki (2003) described this species based on a large number of females and a single male but in none of our samples could we find a male. Tylencholaimus parvus along with T. chathami Yeates, 1979 ; T. micronanus Yeates, 1979 , T. nanus Thorne, 1939 and T. ibericus Peña-Santiago and Coomans, 1994 constitute a group of very closely related species with minor differences in morphometrics (see Yeates 1979; Thorne 1939; Peña-Santiago and Coomans 1994).

Tylencholaimus confusus Ahmad and Araki, 2003

( Figure 3F–L ; Table 2)

Description

Female. Lip region cap-like, conical, offset from the body by deep constriction; lips moderately separate and angular with inner part elevated and protruding. Labial and cephalic papillae slightly protruding. Amphids cup-shaped, their aperture slit-like, occupying about half of lip region width. Odontostyle 0.8–0.9 times the lip region width long, with aperture about one-quarter of its length. Guiding ring single, at 0.66–0.75 times the lip region width from anterior end. Odontophore rod-like, about 1.5–1.6 times the odontostyle length, with well-developed basal flanges appearing as two posteriorly directed lobes; the flanges are very distinct in fresh specimens. Anterior slender part of pharynx weakly muscular expanding abruptly into an elongate basal bulb, occupying about 44–48% of neck length from anterior end. Cardia short, conoid. Genital system monodelphic–prodelphic; posterior genital branch represented by a small sac, measuring 9–12 µm. Vagina cylindrical, bent forward, about half of the corresponding body width deep. Vulva transverse. Tail short, conoid, ventral side straight, dorsal side convex, with rounded tip, and with a pair of caudal pore on each side.

Male. Not found.

Habitat and locality

Soil around roots of forest trees from Uleungdo, Gyeongsangbuk-do, South Korea.

Remarks

Tylencholaimus confusus Ahmad and Araki, 2003 is a unique species in the genus Tylencholaimus , characterized by the presence of a flanged odontophore rather than basal knobs. Ahmad and Araki (2003), while describing this species, emphasized this apomorphic state of character which is clearly a divergence from all the species of the group and might represent a new genus when more similar forms are recorded. We collected several specimens of this species from Uleungdo. Interestingly, we did not find any male in the Korean population, although in the Japanese population males were quite common. However, our current specimens completely fit the description and measurements of the type population except for having a slightly wide amphidial aperture (versus 4 µm), longer expanded part of the pharynx (versus 83–93 µm), and a slightly lower b value (versus b = 3.8–4.4).

Figures

Figure 3. (A–E) Tylencholaimus parvus Ahmad and Araki, 2003. (A) Anterior region; (B) anterior end showing amphid; (C) pharyngeal expansion; (D) female genital system; (E) female posterior end. (F–L) Tylencholaimus confusus Ahmad and Araki, 2003. (F) Anterior end; (G) anterior end showing amphid; (H) pharyngeal expansion; (I) pharyngointestinal junction; (J) vulval region; (K) prerectum–intestine junction; (L) female posterior end.