Axonchium paracingulatum, 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 : 32-36

Axonchium paracingulatum sp. nov.

urn:lsid:zoobank.org:act:2BD7DF2B-E205-45F7-B856-B280828FE218

Figs 11–12 , Table 8

Diagnosis

Axonchium paracingulatum sp. nov. is characterized by having a 2.5–2.8 mm long body; lip region offset by constriction; odontostyle fusiform, 10–11 µm long; both parts of the pharynx separated by deep constriction; anterior uterine sac 1.6–2.2 times mid-body diameter long; vaginal lumen highly expanded in the middle, somewhat diamond-shaped in lateral view; male with 69 µm long and massive spicules; lateral guiding pieces slightly ventrally arcuate, 21 µm long with bifurcated distal ends; seven irregularly spaced ventromedian supplements, beginning just in front of proximal end of spicules and tail broadly conoid with rounded terminus.

Etymology

The new species is named A. paracingulatum because of its resemblance with A. cingulatum Nair, 1973 .

Material examined

Holotype INDIA • ♀; Maharashtra State, Sangli District, Chandoli National Park ; 17°11ʹ30ʺ N, 73°46ʹ30ʺ E; 10–15 cm depth; 14 Apr. 2016; roots of grasses (unidentified); slide reference number AMU/ZD/ NC/ Axonchium paracingulatum /1.

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

Type habitat and locality

Soil samples collected around the roots of grasses (unidentified) from Chandoli National Park, Sangli District, Maharashtra State, India.

Description

Female

Body curved ventrad upon fixation, 2.5–2.8 mm long. Cuticle with fine transverse striations, about 2 µm thick at anterior region, 2–3 µm at mid-body and 6–7 µm on tail tip. Lateral chords 6–9 µm wide, about 1/ 9 to 1/ 7 (11–13.6%) of mid-body diameter. Lateral, dorsal and ventral body pores indistinct. Lip region distinctly offset, twice as wide as high, or about 1/ 7 to 1/ 5 (14–19%) of body diameter at neck base. Lips high, less conoid, outer and inner portions demarcated by slight depression. Amphid fovea stirrup-shaped, their aperture occupying about 0.6–0.7 times lip region diameter, fusus just opposite to odontophore level. Guiding ring single, at 0.9–1.0 times lip region diameter from anterior end. Odontostyle fusiform, 5.0–5.5 times as long as wide, or 1.0–1.1 times lip region diameter long, its aperture about ⅓ of its length. Odontophore simple, rod-like, 1.2–1.4 times as long as odontostyle. Nerve ring encircling anterior slender part of pharynx at 19–22% 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 12–15 times as long as wide, or 8.0–10 times longer than body diameter at neck base, and occupying about 2/ 3 (63–67%) of total neck length, enclosed in a thick muscular sheath with straight muscular bands. Only dorsal pharyngeal gland and its orifice visible: DO = 34–38; DN = 35.5–38.3; DO–DN = 0.1–0.9. Cardia oblong, 1.3–1.6 times as long as wide, occupying about ¼ to ⅓ (24–30%) of corresponding body diameter.

Genital system mono-opisthodelphic. Anterior genital branch represented by a simple uterine sac with a slight proximal constriction, measuring 152–221 µm or 2.5–3.3 times corresponding body diameter long, and occupying about 5.8–7.8% of total body length; mostly containing ovoid sperms. Posterior branch well developed; ovary reflexed, not reaching oviduct-uterus junction, measuring 94–201 µm long with squamous shaped oocytes arranged in a single row except near tip; oviduct joining ovary subterminally, measuring 101–145 µm or 1.6–2.2 times mid-body diameter long, consisting of a long slender part with prismatic cells and a well developed pars dilatata with distinct lumen; oviduct-uterus junction marked by a sphincter; uterus 95–170 µm or 1.5–2.8 times mid-body diameter long, differentiated into a relatively large proximal region with wide lumen, a long narrow intermediate region, and a large spherical distal pars dilatata with clear lumen. Vulva transverse. Vagina slightly bent posteriorly, extending inwards about ½ (46–55%) of corresponding body diameter; vagina lumen highly expanded in middle, somewhat diamond-shaped in lateral view, its wall not differentiated from body cuticle; pars proximalis vaginae longer than wide, 10–13 × 4–6 µm, surrounded by weak circular musculature; pars refringens vaginae absent; pars distalis vaginae 21–24 µm long with convex walls. Prerectum 7.6–10.4 and rectum 0.9–10 times anal body diameter long. Tail short, broadly 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 ovoid, measuring 5–6 × 1–2 µm. In addition to adcloacal pair, located at 17 µm from cloacal aperture, a series of seven irregularly spaced ventromedian supplements, beginning at 33 µm from adcloacal pair, or just in front of proximal end of spicules. Copulatory muscles conspicuous, beginning from posterior end of spicules and continuing until the level of last supplements. Spicules massive, strongly bent ventrally with crenate inner walls; total length along the arc 1.1 times as long as chord, 4.0 times maximum width and 1.5 times body diameter at cloacal aperture. Curvature about 128˚. Dorsal contour irregularly convex with comparatively robust posterior end; ventral contour concave with a prominent hump, located at 43.4% of spicule total length from its anterior end; head comparatively slender, slightly curved, occupying about 24.6% of spicule total length; median piece robust with crenate outer walls, 10.4 times as long as wide, and occupying about 29.4% of spicule maximum width; posterior end 7 µm wide. Lateral guiding pieces distinctly sclerotized, slightly ventrally arcuate with bifurcated distal end, 5.3 times as long as wide or about ⅓ (30.4%) of total spicule length. Prerectum 8.4 and rectum 1.3 times cloacal body diameter long. Tail short, dorsally convex, conoid with broadly rounded terminus. Caudal pores two on each side.

Taxonomic remarks

In its large body size, long anterior uterine sac and the shape of the vagina, the new species comes close to A. cingulatum Nair, 1973 , but differs in the nature of the cuticle towards the anterior ends (thin vs very thickened); obscure body pores (vs distinct); the shape of the lips (comparatively high vs small and low); shorter odontostyle (10–11 vs 12–13 µm); shorter odontophore (14–16 vs 23 µm); junction between two parts of the pharynx separated by a deep constriction (vs separated by an isthmus-like portion); in intestino-prerectal junction (simple vs surrounded by a sphincter-like structure with long microvilli in the intestine present just anterior to the sphincter) and presence of male (vs not found but spindle-shaped sperms are present).

In body size, shape of spicules and lateral guiding pieces, the new species comes close to A. heynsi Nair, 1973 , but differs in the nature of the cuticle striations (with fine transverse striations vs distinct transverse striations); shape of vagina (vs the vagina abruptly narrows within the sphincter); middle tubular part of uterus relatively less narrow (vs very narrow); longer prerectum in male (8.4 vs 12–18 times the cloacal body diameter long); longer spicules (69 vs 41–58 µm long with comparatively slender and more arcuate head region), median piece ending with bluntly conoid projection towards the head region of spicules (vs ending with a long sharp pointed projection); longer lateral guiding pieces (21 vs 12–16 µm long); in shape of median piece (with blunt projection in anterior region of spicule vs simple with fine projection) and first ventromedian supplement located just in front of proximal end of spicules (vs at about ½ the anal body diameter anterior to the proximal end of the spicules).

The new species also resembles to A. manalicum Ali, Jairajpuri & Coomans, 1974 in the large body size, large and robust spicules and tail shape but differs in the shape of the vagina (vs not expand in middle, narrowing within the sphincter); shorter prerectum in male (8.4 vs 11–13 times cloacal body diameter long); in shape of spicules (vs spicule walls smooth and relatively less thick), spicule ventral arm with prominent hump (vs indistinct), median piece robust with irregularly crenate walls (vs relatively less thick with smooth walls); first ventromedian supplement located just in front of proximal end of spicules (vs behind the proximal end of spicules).

Figures

Fig. 11. Axonchium paracingulatum sp. nov. A, H. Holotype ♀ (AMU/ZD/Axonchium paracingulatum sp. nov. /1). B, I–K. Paratype 1, ♂ (slide 2). C–G, L. Paratype 3, ♀ (slide 2). 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. Vulva. H. Female genital system. I. Male posterior region. J. Spicule. K. Lateral guiding piece. L. Female posterior end.

Fig. 12. Axonchium paracingulatum sp. nov. (LM photographs). A–G, K. Paratype 3, ♀ (slide 3). H– J. Paratype 2, ♂ (slide 2). A. Anterior region.B. Anterior end showing amphid. C. Junction between two parts of the pharynx. D. Cardia. E. Vulva and vagina. F–G. Female genital branches. H. Ventromedian supplements. I. Male posterior end. J. Arrow indicating lateral guiding piece and distal end of spicule. K. Female posterior end. Scale bars: A–E, I–K = 10 µm; F–G = 20 µm; H = 50 µm.