Axonchium mizukuboi, 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 : 1510-1514

Axonchium mizukuboi sp. nov.

( Figures 1A–N , 2A–J ; Table 1)

Description

Female. Body curved ventrad upon fixation, tapering towards anterior extremity, posteriorly terminating in a short hemispheroid tail. Cuticle with distinct transverse striations, 3–4 µm thick at mid-body and 8–10 µm at tail. Lateral chords about onefifth of body width at mid-body, with distinct glands throughout the body length Lateral, dorsal and ventral body pores indistinct. Lip region offset, about twice as wide as high or about one-sixth as wide as body width at neck base; lips amalgamated. Amphids cup-shaped, their aperture about as wide as lip region width. Odontostyle fusiform, 1.1–1.2 times lip region width long, its aperture about one-third of its length. Guiding ring ‘single’, at 1.1–1.2 times lip region width from anterior end. Odontophore linear, 1.4–1.5 times the odontostyle length. Nerve ring encircling the anterior slender part of pharynx at 18–19% of neck length from anterior end. Anterior part of pharynx muscular, separated from the posterior expanded part by a short isthmus-like section, the latter occupying about 72–75% of total neck length and enclosed in muscle sheath with straight bundles. Cardia cylindroid, two-fifths to three-fifths of corresponding body width long. Genital system mono-opisthodelphic; anterior genital branch represented by a long uterine sac with rudimentary oviduct at its proximal end, 130–150 µm or 2.7–3.2 times the corresponding body width long and filled with spermatozoa. Posterior genital branch well developed; ovary reflexed, not reaching or surpassing the oviduct–uterus junction, measuring 180–325 µm with oocytes arranged in a single row except near tip. Oviduct joining the ovary subterminally, measuring 120–200 µm, consisting of a long slender part with prismatic cells and a well-developed pars dilatata with wide lumen. Uterus measuring 90–150 µm, differentiated into three parts, distal and proximal expanded parts with wide lumen and intermediate convoluted part with narrow lumen. Sphincter at oviduct–uterus junction present in both the genital branches. Vulva transverse. Vagina extending inward, about half of corresponding body width deep; pars proximalis vaginae 14–15 µm long with almost straight walls; encircled by circular muscles; pars refringens vaginae with two rectangular sclerotized pieces, each measuring 4–5 × 3 µm (cw = 10 µm); pars distalis vaginae 4–5 µm with slightly concave walls. Prerectum 7–9 anal body widths long. Rectum about 1.1–1.3 times anal body width long. Tail short, hemispheroid, about 0.7–1.0 times anal body width long. Caudal pores two on each side.

Male. Similar to female in general morphology, except for posterior region being more curved ventrad because of the presence of copulatory muscles. Supplements, an adanal pair and seven evenly spaced ventromedians, starting above the range of spicules. Spicules arcuate, robust, with thickened distal end, about 1.5 times anal body width long. Lateral guiding pieces simple, rod-like with thickened distal tip, about one-quarter of spicule length. Prerectum 5.5 anal body widths long. Rectum about as long as anal body width. Tail, convex conoid to hemispheroid about 0.75 times anal body width long. Two caudal pores on each side.

Type habitat and locality

From grasslands of Ishigaki Island, south Japan, Japan

Type specimens

Holotype female on slide Axonchium mizukuboi sp. nov. / 1; paratype females and males on slides Axonchium mizukuboi sp. nov. / 2–4; deposited with the nematode collection of the Department of Zoology, Aligarh Muslim University, India.

Diagnosis and relationships

Axonchium mizukuboi sp. nov. is characterized by having 2.3–2.4 mm long body; 10 µm long odontostyle; isthmus-like section between two parts of pharynx; cylindrical cardia; anterior uterine branch large with rudimentary oviduct; pars refringens vaginae two rectangular sclerotized pieces; males with arcuate spicules having thickened distal ends; lateral guiding pieces simple rod-like with thickened distal tip; seven regularly spaced ventromedian supplements starting above the range of spicules and hemispheroid tail.

In having well-developed vaginal sclerotization and absence of disc-like structure between vulva and vagina, the new species belongs to the subgenus Axonchium (Metaxonchium) and comes close to Axonchium coronatum ( de Man, 1906) Thorne and Swanger, 1936 in having rudimentary ovarian mass and short isthmus-like constriction between two parts of pharynx but differs from it in having shorter body length (2.3–2.4 vs 2.9–4.2 mm), narrower lip width (8–9 vs 10–14 µm), shorter odontostyle (10 vs 13–16 µm), in the shape of pars refringens vaginae (rectangular vs heart-shaped), in the shape and size of spicules (robust vs slender, 1.5 vs 1.8–1.9 times anal body width long) and in the number of ventromedian supplements (7 vs 9–11).

The new species also comes close to Axonchium zealandicum Naz, Ahmad and Jairajpuri, 2007 in having rudimentary ovarian mass and short isthmus-like constriction between two parts of pharynx but differs from it in having shorter and slender body (2.3–2.4 vs 2.7 mm, a = 46–52 vs 39.3), narrower lip region (8–9 vs 15 µm), shorter odontostyle (10 vs 13.5 µm), in the shape of pars refringens vaginae (rectangular vs drop-shaped with concave outer wall), absence of disc-like structure in vagina (vs presence), in the shape and size of spicules (robust, 45 µm vs less robust, 78 µm), in the number and arrangement of ventromedian supplements (7 vs 10, starting within the range of spicules), and in the shape and size of tail (hemispheroid, c = 77.4 to v = 93.4 vs conoid, c = 73).

Etymology

The new species is named after Dr T. Mizukubo, team leader Nematode Research Group, National Agriculture Research Centre, Tsukuba, Japan for kindly providing specimens from his collection.

Figures

Figure 1. Axonchium mizukuboi sp. nov. (A) Entire female, (B) entire male, (C) anterior region, (D) anterior end showing amphid, (E, F) junction between two parts of pharynx, (G, H) pharyngointestinal junction, (I) female genital system, (J) vulval region, (K) female posterior end, (L) male posterior region, (M) spicule, (N) lateral guiding piece.

Figure 2. Axonchium mizukuboi sp. nov. (A) Anterior region, (B) anterior end showing amphid, (C) junction between two parts of pharynx, (D) pharyngointestinal junction, (E, F) vulval regions, (G) anterior uterine sac showing rudimentary ovarial mass, (H) female posterior end, (I) ventromedian supplements, (J) male posterior end. (Scale bars: A–E, G–J = 10 µm;F = 20 µm).