Axonchium nilgiriense, Kumar & Ahmad, 2023

Kumar, Sumit & Ahmad, Wasim, 2023, Six new and four known species of the genus Axonchium Cobb, 1920 (Nematoda: Dorylaimida: Belondiroidea) from the Western Ghats of India, European Journal of Taxonomy 857, pp. 1-56 : 27-31

Axonchium nilgiriense sp. nov.

urn:lsid:zoobank.org:act:D7DA66DD-824A-4755-8107-44E30DD1394E

Figs 9–10 , Table 7

Diagnosis

Axonchium nilgiriense sp. nov. is characterized by having a 1.4–1.6 mm long body; lip region offset; amphids stirrup-shaped; odontostyle fusiform, 8–9 µm long; two parts of the pharynx separated by deep constriction; anterior uterine sac, 2.6–4.1 times the mid-body diameter long; vulva transverse, vagina strongly bent posteriad, almost as deep as corresponding body diameter; spicules robust, strongly arcuate, 37–41 µm long; lateral guiding pieces arcuate, 15–16 µm long with thickened distal end; 3–4 widely spaced ventromedian supplements, beginning at just in front of proximal end of the spicules and tail bluntly conoid with rounded terminus.

Etymology

The new species is named after its type locality.

Material examined

Holotype INDIA • ♀; Tamil Nadu State, Nilgiri District, Mudumalai National Park ; 11°35ʹ0ʺ N, 76°33ʹ0ʺ E; 10–15 cm depth; 14 Nov. 2016; roots of grasses (unidentified); slide reference number AMU/ZD/ NC/ Axonchium nilgiriense /1.

Paratypes INDIA • 5 ♀♀, 1 ♂; same collection data as for holotype; slide reference number AMU/ZD/ NC/ Axonchium nilgiriense /2–5 • 3 ♀♀, 2 ♂♂; same collection data as for holotype; slide reference number AMU/ZD/NC/ Axonchium nilgiriense /6–7, nematode collection of the Zoological Survey of India, Kolkata, India .

Type habitat and locality

Soil samples collected around the roots of grasses (unidentified) from Mudumalai National Park, Nilgiri District, Tamil Nadu State, India.

Description

Female

Body slender, curved ventrad upon fixation, 1.4–1.6 mm long. Cuticle with fine transverse striations, about 1 µm thick at anterior region, 2 µm at mid-body, 4–5 µm on tail tip in females and 3–4 µm in males. Lateral chords 3–5 µm wide, about 1/ 10 to 1/ 5 (10–18%) of mid-body diameter, with weakly developed glandular bodies in posterior region, 10–18 in number. Lateral, dorsal and ventral body pores indistinct. Lip region distinctly offset, twice as wide as high, or about ¼ to slightly less than ⅓ (25–30%) of body diameter at neck base. Lips high, bluntly conoid and separate. Amphid fovea stirrup-shaped, their aperture occupying about 0.6–0.8 times lip region diameter, fusus posterior to odontophore level. Guiding ring single, at 0.6–1.0 times lip region diameter from anterior end. Odontostyle fusiform, 3.5– 5.3 times as long as wide, or 0.9–1.1 times lip region diameter long, its aperture occupying about ⅓ of its length. Odontophore simple, rod-like, 1.1–1.6 times as long as odontostyle. Nerve ring encircling anterior slender part of pharynx at 18–24% of neck length from anterior end. Anterior slender part of pharynx quite muscular, separated from posterior expanded part by a deep constriction. Expanded part of pharynx 14–22 times as long as wide, or 9.3–14 times as long as body diameter at neck base, and occupying about ½ to two-thirds (54–64%) of total neck length, enclosed in a thick muscular sheath with straight bands. Only dorsal pharyngeal gland and its orifice visible: DO = 37.8–49.2; DN = 38.8–49.4; DO–DN = 0.2–1.2. Cardia oblong, 1.4–2.0 times as long as wide, occupying about ⅓ to ½ (34–46%) of corresponding body diameter.

Genital system mono-opisthodelphic. Anterior genital branch represented by a simple uterine sac with slight proximal constriction, measuring 76–111 µm or 2.6–4.1 times corresponding body diameter long, and occupying about 5.0–6.7% of total body length; mostly containing spindle-shaped sperms. Posterior branch well developed; ovary reflexed, not reaching oviduct-uterus junction, measuring 44–120 µm long with squamous shaped oocytes arranged in a single row except near tip; oviduct joining ovary subterminally, 45–92 µm or 1.6–3.4 times mid-body diameter long, consisting of a long slender part with prismatic cells and a wide pars dilatata with distinct lumen; oviduct-uterus junction marked by a sphincter; uterus 40–108 µm or 1.3–4.0 times mid-body diameter long, differentiated into a relatively long proximal region with wide lumen, a narrow intermediate region, and a large spherical distal pars dilatata with distinct lumen. Vulva transverse with wide opening. Vagina bent posteriorly at the right angle with constriction in middle, extending inwards about two-thirds to almost as deep as (70–93%) corresponding body diameter, vaginal walls thick, not differentiated from body cuticle; pars proximalis vaginae longer than wide, 7–12 × 2–4 µm, surrounded by circular muscles; pars refringens absent; pars distalis 12–14 µm long. Prerectum 7–12 and rectum 1.2–1.7 times anal body diameter long. Tail bluntly conoid with rounded terminus. Caudal pores two on each side.

Male

Similar to females in general morphology, except for posterior region of body being more curved ventrad. Genital system diorchic, with oppositely outstretched testes; sperms spindle-shaped, measuring 5–6 2 µm. In addition to adcloacal pair, located at 5–7 µm from cloacal aperture, 3–4 weakly developed, spaced ventromedian supplements, beginning just in front of proximal end of spicule; first located at 26–31 µm from adcloacal pair, second at 16–18 µm from first, third at 29–38 µm from second and fourth at 9–11 µm from third ventromedian supplement. Copulatory muscles conspicuous, beginning from level of middle of spicules and continuing until the level of last supplements. Spicules robust, strongly arcuate, total length along arc 1.0–1.1 times as long as chord, or 4.1–5.2 times maximum width, and 1.5–1.6 times body diameter at cloacal aperture. Curvature about 113˚–124˚. Dorsal contour regularly convex; ventral contour concave, with prominent hump located at 27–28% of spicule total length from its anterior end; head 3–6 µm long, occupying about 8–15% of total spicule length; median piece simple, 8.5–13.3 times as long as wide, and occupying about 30–57% of spicule maximum width; posterior end 3–4 µm wide, bent ventrally. Lateral guiding pieces lightly sclerotized, ventrally arcuate with thickened distal end, about 8–10 times as long as wide or ⅓ to 2/ 5 of spicule length. Prerectum 8.4–8.7 and rectum 1.5–1.7 times cloacal body diameter long. Tail less conoid, having slight depression on ventral side, bluntly truncated terminus. Caudal pores two on each side.

Taxonomic remarks

The new species comes close to A. elegans Jairajpuri, 1964 and A. parasaccatum Rahman, Jairajpuri & Ahmad, 1985 in general body morphology, but it distinctly differs in the nature of the vagina (vagina almost as deep as corresponding body diameter vs about ½); strongly arcuate spicules with curved posterior ends (vs spicules slightly arcuate and unusually wide with blunt distal end); shape of lateral guiding pieces (arcuate vs almost straight to slightly curved) and tail shape (bluntly conoid vs obtusely rounded).

From A. parasaccatum , it differs in having a shorter body (1.4–1.6 vs 1.87–1.9 mm); narrower lip region (7–8 vs 9–10 µm wide); shorter odontostyle (8–9 vs 10–11 µm); shorter expanded part of pharynx (54–64 vs 67–69% of total neck length); anterior vulva position (V = 51–54 vs 58–60); arrangements of ventromedian supplements (beginning just in front of proximal end of spicules vs anterior to proximal end of spicules); in having short robust, strongly arcuate spicules (37–41 vs 49–53 µm long, comparatively less arcuate and slender spicules); in nature of lateral guiding pieces (arcuate with thickened distal end vs almost straight with bifurcated distal end) and tail shape (bluntly conoid with rounded terminus vs hemispheroid).

The new species also resembles A. cooverkolli Dhanam & Jairajpuri, 1998 in its posterior inclined vagina, long anterior uterine sac and arrangements of ventromedian supplements, but differs in having a longer body (1.4–1.6 vs 1.1–1.3 mm long); longer and strongly arcuate spicules (37–41 vs 30 µm long, relatively less arcuate); lower number of ventromedian supplements (3–4 vs 6); lateral guiding pieces large and ventrally arcuate (15–16 vs 9 µm long, rod-shaped with blunt ends); and in tail shape (bluntly conoid with rounded terminus vs broadly rounded).

Figures

Fig. 9. Axonchium nilgiriense sp. nov. A, C–F, G, K. Paratype 4, ♀ (slide 4). B, H–J. Paratype 5, ♂ (slide 4). A. Entire female. B. Entire male. C. Anterior region. D. Anterior end showing amphid. E. Junction between anterior slender and posterior expanded part of pharynx. F. Cardia. G. Female genital system. H. Male posterior region. I. Spicule. J. Lateral guiding pieces. K. Female posterior end.

Fig. 10. Axonchium nilgiriense sp. nov. (LM photographs). A–D. Paratype ♀, (slide 2). E. Paratype 4, ♀. I–K. Paratype 5, ♂ (slide 4). F–H, L. Paratype 6, ♀ (slide 5). A. Anterior region. B. Anterior end showing amphid. C. Junction between two parts of the pharynx. D. Cardia. E–F. Vulva and vagina. G– H. Female genital branches. I. Male posterior end. J. Arrow indicating lateral guiding piece. K. Arrows indicating ventromedian supplements. L. Female posterior end. Scale bars = 10 µm.