Axonchium singaporense, Ahmad & Naz, 2010

Ahmad, Wasim & Naz, Tabbasam, 2010, Two new and two known species of the family Belondiridae Thorne, 1939 (Nematoda: Dorylaimida) from Singapore, Journal of Natural History 44 (41 - 42), pp. 2465-2479 : 2466-2468

Axonchium singaporense sp. nov.

( Figures 1A–M, 2A–I ; Table 1)

Description

Female. Body slightly curved ventrad upon fixation, tapering towards both extremities. Cuticle finely striated, 3–4 µm thick at mid body and 7–9 µm at tail. Lateral chords about one-quarter as wide as body width at mid body. Lateral, dorsal and ventral body pores indistinct. Lip region narrow, rounded, continuous with body, about onethird as wide as body width at neck base. Cephalic framework distinctly sclerotized. Amphids cup-shaped, their aperture about 0.8 times as wide as lip region width. Odontostyle fusiform, about as long as lip region width, its aperture about one-third of its length. Guiding ring single, at about one lip region width from anterior end. Odontophore linear, 1.6 times odontostyle length. Nerve ring at 23–26% of neck length from anterior end. Anterior part of pharynx muscular and separated from posterior expanded part by deep constriction or two parts of the pharynx abutting each other, the latter occupying 52–65% of total neck length and enclosed in muscle sheath with straight bundles. Cardia rounded to conoid, about half of the corresponding body width long. Genital system mono-opisthodelphic. Anterior branch represented by a short uterine sac, 1.4–2.1 times corresponding body width long. Posterior branch well developed; ovary reflexed, not reaching or surpassing the oviduct– uterus junction, measuring 85–95 µm with oocytes arranged in a single row except near tip. Oviduct joining ovary subterminally, measuring 65–75 µm, consisting of a long slender part with prismatic cells and a slightly wider pars dilatata with clear lumen, its inner part more refractive, being encircled by a muscular ring. Sphincter present at oviduct–uterus junction. Uterus a simple tube, 35–50 µm long. Vulva transverse. Vagina narrow and directed posteriad, extending inwards about twothirds of the corresponding body width deep; pars proximalis vaginae 13–18 µm long with almost straight walls and surrounded by circular muscles; pars refringens vaginae absent; pars distalis vaginae 3–5 µm with slightly rounded walls. Prerectum 5.0–6.3 times anal body width long. Rectum 1.1–1.3 times anal body width long. Tail short, broadly rounded, clavate, 0.8–0.9 times anal body width long. Caudal pores two on each side.

Male. Not found.

Type habitat and locality

Soil around the roots of forest trees from Kent Ridge Park, near the National University of Singapore, Singapore.

Type specimens

Holotype female on slide Axonchium singaporense sp. nov. / 1; paratype females on slides Axonchium singaporense sp. nov. / 2–5; deposited with the nematode collection of the Department of Zoology, Aligarh Muslim University, India.

Diagnosis and relationships

Axonchium singaporense sp. nov. is characterized by having body 1.1–1.3 mm long, continuous lip region, cephalic framework distinctly sclerotized, odontostyle 6 µm long, posteriorly directed vagina, anterior uterine sac 30–50 µm long, clavate tail and absence of male.

In having a continuous lip with amalgamated lips, the new species belongs to the group of species placed under the subgenus Syncheilaxonchium Coomans and Nair, 1975 . In this subgenus, because of the presence of a posteriorly directed vagina, the new species appears most closely related to Axonchium indicum Siddiqi, 1964 , Axonchium asacculum Siddiqi, 1968 and Axonchium banaticum Popovici, 1990 , however, it is distinct from all by the presence of labial sclerotization. From A. indicum , the new species further differs in having a more slender body (a: 52–59 vs 43–47), slightly shorter anterior uterine sac (G1: 2.4–4.2% vs 5.0–6.5%), in the shape of the tail (clavate vs obtusely rounded), and in the thickness of the tail cuticle (7–9 vs 5.5–6.0 µm). From A. asacculum , the new species differs in having a more slender body (a: 52–59 vs 37–49), shorter odontostyle (6 vs 7–8 µm) and in the presence of an anterior uterine sac (vs anterior uterine sac absent).

From A. banaticum , it differs in having a longer body (L: 1.1–1.3 vs 1.8–2.0 mm), narrower lip region (6–7 vs 8–9 µm), shorter odontostyle (6 vs 8–9.5 µm), comparatively shorter pharynx (b: 2.2–2.7 vs 3.2–3.5), in the presence of an anterior uterine sac (vs anterior uterine sac absent), and in the shape of the tail (clavate vs rounded).

The new species also resembles Axonchium siddiqii Coomans and Nair, 1975 in having a posteriorly directed vagina and in tail shape but differs from it in having a comparatively slender body (a: 52–59 vs 38–42), continuous lip region with distinct cephalic sclerotization (vs offset lip region without sclerotization), shorter odontostyle (6 vs 8–9 µm), comparatively shorter anterior uterine branch (G1: 2.4–4.2% vs 5–6.5%) and in the absence of male (vs male present).

Etymology

The species name refers to Singapore, the country of origin.

Figures

Figure 2. Axonchium singaporense sp. nov. (A–C) anterior region, (D) junction between two parts of pharynx, (E) pharyngo–intestinal junction, (F,G) vulval region, (H) female posterior region (dorsoventral), (I) female posterior region (lateral). Scale bars A–C, 10 µm; D–I, 20 µm.