Dorylaimellus (Axodorylaimellus) paracrassidens, Ahmad & Naz, 2010

Ahmad, Wasim & Naz, Tabbasam, 2010, Four new and one known species of Belondiroidea (Dorylaimida: Nematoda) from Japan, Journal of Natural History 44 (25 - 26), pp. 1509-1530 : 1524-1528

Dorylaimellus (Axodorylaimellus) paracrassidens sp. nov

( Figures 7A–H , 8A–F ; Table 4)

Description

Female. Body curved ventrad upon fixation, tapering towards both extremities. Cuticle finely striated, 1.0–1.5 µm thick at mid-body and 3–4 µm at tail. Lateral chords occupying about one-third of corresponding body width at mid-body. Lateral, dorsal and ventral body pores indistinct. Lip region distinctly offset by constriction, about twice as wide as high or about one-quarter as wide as body width at neck base, lips amalgamated, perioral disc present. Four cuticularized pieces present around oral opening. Amphids large stirrup-shaped, their aperture about as wide as lip region width. Odontostyle linear, about as long as lip region width, its aperture about one-third of its length. Odontophore poorly flanged, 1.4–2.0 times the odontostyle length. Nerve ring encircling the anterior part of pharynx at 31–32% of neck length from anterior end. Pharyngeal expansion abrupt; expanded part occupying about 50–57% of total neck length, enclosed in a thick sheath of dextrally spiral muscles. Cardia short, rounded, about one-quarter to one-third of corresponding body width long. Genital system didelphic–amphidelphic; both the sexual branches almost equally developed. Ovaries reflexed, measuring 13–17 µm (anterior) and 12–16 µm (posterior) with oocytes arranged in a single row except near tip. Oviduct joining ovary subterminally, measuring 10–15 µm (anterior) and 10–14 µm (posterior) long. Uterus a small tube, measuring 10–15 µm (anterior) and 10–16 µm (posterior). Vulva transverse. Vagina extending inward, about one-half of corresponding body width; pars proximalis vaginae 5–6 µm, with curved walls, encircled by circular muscles; pars refringens vaginae absent; pars distalis vaginae 1.0–1.2 µm, with rounded walls. Prerectum 2.5–4.0 anal body widths long. Rectum about as long as anal body width. Tail short, subclavate 1.3–1.9 anal body widths long, with inner protoplasmic core first cylindrical and then conoid. Caudal pores two on each side.

Male. Not found.

Type habitat and locality

Soil from paddy field, Sonai, Taketomi, Iriamote Island, Japan.

Type specimens

Holotype female on slide Dorylaimellus (A.) paracrassidens sp. nov. /1; paratype females and males on slides Dorylaimellus (A.) paracrassidens sp. nov. /2–5; deposited with the nematode collection of the Department of Zoology, Aligarh Muslim University, India.

Diagnosis and relationships

Dorylaimellus (A.) paracrassidens sp. nov. is characterized by having 0.4–0.5 mm long body; 4–5 µm long, slender odontostyle; expanded part of pharynx 48–57% of total neck length; transverse vulva; amphidelphic female genital system; 5–5.5 anal body widths long prerectum and short subclavate tail.

The new species belongs to the subgenus Axodorylaimellus Jairajpuri and Ahmad, 1980 and is very close to Dorylaimellus (A.) crassidens ( Siddiqi, 1983) Jairajpuri and Ahmad 1992 , but differs from it in having robust body (a = 19.8–29.6 vs 31–36), thin slender odontostyle (vs thick-walled robust odontostyle) and differently shaped tail (subclavate with rounded terminus vs subclavate with rather conical terminus).

The new species is also close to Dorylaimellus (A.) aghai ( Siddiqi, 1983) Jairajpuri and Ahmad, 1992 and Dorylaimellus (A.) caffrae Kruger, 1965 in its small body size but differs from the former in the nature of its cuticle (fine striations vs distinct striations), in having a poorly flanged odontophore (vs strongly flanged odontophore) and in tail shape (subclavate vs subcylindrical).

From D. (A.) caffrae , the new species differs in having cuticle with fine striations (vs distinct striations), stirrup-shaped amphids (vs calyx-shaped); poorly flanged odontophore (vs strongly flanged odontophore) and subclavate tail (vs cylindrical).

Remarks

The subgenus Axodorylaimellus Jairajpuri and Ahmad, 1980 of the genus Dorylaimellus constitutes a group of seven closely related species (an eighth is added here) with overlapping measurements and differing only in a few morphological features. Their body size ranges from 0.32 to 0.58 mm and the males are not recorded in any of these species. Dorylaimellus (A.) crassidens ( Siddiqi, 1983) Jairajpuri and Ahmad, 1992 differs from all other species in having a distinctly thickened odontostyle, while D. (A.) aghai ( Siddiqi, 1983) Jairajpuri and Ahmad, 1992 has prominent body striations and a subcylindrical tail. Dorylaimellus (A.) parvulvus Thorne, 1939 and D. (A.) caffrae Kruger, 1965 differ from all the other species of this group in having a cylindrical tail. These two species are differentiated on the basis of lateral chords and size of prerectum, the former has exceptionally narrow lateral chords and long prerectum (5 vs 2.5–3 times anal body widths). Recently, Andrássy (2009) considered D. caffrae a synonym of D. (A.) parvulus but this has not been accepted here. Dorylaimellus (A.) cataracticus Andrássy, 1968 differs from other species in having s strongly offset lip region, whereas, Dorylaimellus (A.) deviatus Baqri and Jairajpuri 1969 differs from other species in having a slightly offset lip region. Our present new species, D. (A.) paracrassidens sp. nov. although very close to D. (A.) crassidens differs in the nature of its odontostyle. Dorylaimellus (A.) iari Siddiqi, 1983 is the smallest known species in this group with a short hemispheroid tail.

Siddiqi (1983) raised the subgenus Dorylaimellus (Axodorylaimellus) to the rank of a genus, Axodorylaimellus and provided a key to the species under this genus. Jairajpuri and Ahmad (1992) in their book on Dorylaimida did not accept the generic status and retained it as a subgenus under the genus Dorylaimellus . Except for the present new species, no other species has been added to this group after Siddiqi (1983).

Figures

Figure 7. Dorylaimellus paracrassidens sp. nov. (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 8. Dorylaimellus paracrassidens sp. nov. (A) Anterior region, (B) anterior end showing amphid, (C) expanded part of pharynx, (D) vulval region, (E) vulval region in ventral view, (F) female posterior end. (Scale bars: A, B = 10 µm; C–F = 20 µm.).