Axonchium microspiculum, 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 : 21-26

Axonchium microspiculum sp. nov.

urn:lsid:zoobank.org:act:E6E21124-1D3D-4571-84FA-BE2B7B128355

Figs 7–8 , Table 6

Diagnosis

Axonchium microspiculum sp. nov. is characterized by its 1.1–1.22 mm long body; lip region offset by deep constriction; odontostyle fusiform, 7–8 µm long; two parts of the pharynx separated by a deep constriction; anterior uterine sac 1.7–2.3 times the corresponding body diameter long; vulva transverse, vagina slightly bent posteriorly with distinct thickening in the middle; spicules short, slightly arcuate, 20–23 µm long; lateral guiding pieces slightly curved dorsally with bifurcated distal end; two weakly developed ventromedian supplements and obtusely rounded tail.

Etymology

The new species is named A. microspiculum because of its characteristic small-sized spicules.

Material examined

Holotype INDIA • ♀; Kerala State, Idukki District, Vagamon Hill ; 9°41ʹ10.25ʺ N, 76°54ʹ18.82ʺ E; 10–15 cm depth; 31 Oct. 2017; roots of grasses (unidentified); slide reference number AMU/ZD/NC/ Axonchium microspiculum /1.

Paratypes INDIA • 2 ♀♀, 4 ♂♂; same collection data as for holotype; slide reference number AMU/ZD/ NC/ Axonchium microspiculum /2–3 • 1 ♀, 2 ♂♂; same collection data as for holotype; slide reference number AMU/ZD/NC/ Axonchium microspiculum /4, nematode collection of the Zoological Survey of India, Kolkata, India .

Other material

INDIA • 4 ♀♀, 1 ♂; Kerala State, Thiruvananthapuram District, Ponmudi Hill ; 8°45′37″ N, 77°7′0″ E; 10–15 cm depth; 4 Nov. 2017; roots of grasses (unidentified); slide reference number AMU/ZD/ NC/ Axonchium microspiculum /4–6 .

Type habitat and locality

Soil samples collected around the roots of the grasses (unidentified) from Vagamon Hill, Idukki District, Kerala State, India.

Other habitat and locality

Soil samples collected around the roots of the grasses (unidentified) from Ponmudi Hill, Thiruvananthapuram District, Kerala State, India.

Description

Female

Body slightly curved ventrad upon fixation, 1.1–1.2 mm long. Cuticle with fine transverse striations, about 1 µm thick at anterior region, 1–2 µm at mid-body and 3–5 µm on tail tip. Lateral chords 2–4 µm wide, about 1/ 13 to 1/ 7 of mid-body diameter, glandular bodies indistinct. Lateral, dorsal and ventral body pores indistinct. Lip region high, offset by deep constriction, 1.7–2.1 times as wide as high, or about ¼ to 2/ 7 (23–28%) of body diameter at neck base. Lips incompletely separate. Amphid fovea stirrup-shaped, their aperture occupying about 0.7–0.8 times lip region diameter, fusus slightly posterior to odontophore level. Guiding ring single, at 1.0–1.1 times lip region diameter from anterior end. Odontostyle fusiform, 3.5–5.0 times as long as wide, or 1.0–1.2 times lip region diameter long, its aperture occupying about ⅓ of its length. Odontophore simple, rod-like, 1.1–1.3 times as long as odontostyle. Nerve ring encircling anterior slender part of pharynx at 21–25% of neck length from the anterior end. Anterior slender part of pharynx quite muscular, separated from posterior expanded part by a deep constriction. Expanded part of pharynx 12.6–16.5 times as long as wide, or 8.9–10.6 times as long as body diameter at neck base, and occupying about ½ to 2/ 3 (57–64%) of total neck length, enclosed in a thick muscular sheath with straight bands. Only dorsal pharyngeal gland and its orifice visible: DO = 37–45; DN = 38.7–46.3; DO–DN = 0.7–1.6. Cardia oblong, 1.5–2.4 times as long as wide, occupying about ¼ to 2/ 5 (25–41%) of corresponding body diameter.

Genital system mono-opisthodelphic. Anterior genital branch represented by simple uterine sac, measuring 47–65 µm or 1.7–2.3 times mid-body diameter long, and occupying about 4.0–5.9% of total body length, filled with a few scattered spindle-shaped sperms. Posterior branch well developed, strongly convoluted; ovary reflexed, not reaching oviduct-uterus junction, measuring 28–98 µm long with squamous shaped oocytes arranged in a single row except near tip; oviduct joining ovary subterminally, measuring 46–72 µm or 1.5–2.6 times mid-body diameter long, consisting of a long slender part with prismatic cells and a slightly wider pars dilatata with distinct lumen; a distinct sphincter present at oviduct-uterus junction; uterus 33–64 µm or 1.2–2.3 times mid-body diameter long, differentiated into a large proximal region with wide lumen, a long narrow intermediate region, and a spherical distal pars dilatata with distinct lumen. Vulva transverse. Vagina slightly bent posteriorly with a constriction in middle, extending inwards about ½ to two-thirds (55–66%) of corresponding body diameter; vaginal wall not differentiated from body cuticle, but distinctly thickened in middle; pars proximalis vaginae longer than wide, 9–11 × 1.5–3 µm, with somewhat concave walls surrounded by well developed circular musculature; pars refringens vaginae absent; pars distalis vaginae 6–8 µm long. Prerectum 6.0–7.3 and rectum 1.0–1.3 times anal body diameter long. Tail short, obtusely rounded. Caudal pores two on each side.

Male

Similar to female in general morphology, except for posterior region of body being more curved ventrad. Genital system diorchic, with oppositely outstretched testes, surrounded by a thick muscular wall; sperms elongate spindle-shaped, measuring 9–11 × 2 µm. In addition to adcloacal pair, located at 4–5 µm from cloacal aperture, with two widely spaced and weakly developed ventromedian supplements, first at 30–41 µm from adcloacal pair, and the second at 62–75 µm from first supplement. Copulatory muscles less conspicuous, beginning from level of middle of spicules and continuing until the level of last supplement. Spicules slightly arcute, slender and weakly developed; total length along arc 1.0–1.1 times as long as chord, 5.0–5.8 times maximum width, or about equal to the body diameter at cloacal aperture. Curvature about 130–150°. Dorsal contour regularly convex, except its distal end being slightly curved ventrally; ventral contour concave, without distinct hump; head short, with rounded ends, occupying 4.8–9.5% of spicule total length; median piece simple with rounded proximal end, 19–21 times as long as wide and occupying 25% of spicule maximum width; posterior end 2–3 µm wide. Lateral guiding pieces lightly sclerotized, slightly curved dorsally with bifurcate distal end, about 5–7 times as long as wide or about 1/ 5 to ⅓ of spicules length. Prerectum long, 5.0–10.8 and rectum 1.2–1.6 times cloacal body diameter long. Tail similar to than in female but having slight depression on ventral side. Caudal pores two on each side.

Taxonomic remarks

In the presence of only two ventromedian supplements, the new species comes close to A. vallum Ahmad & Jairajpuri, 1982 , A. siddiqii Coomans & Nair, 1975 and A. noreasum Naz & Ahmad, 2012 but differs from the former mainly in having a shorter body length (1.1–1.2 vs 1.6–1.95 mm long); indistinct glandular bodies (vs distinct); shorter odontostyle (7–8 vs 10–12 µm); shorter odontophore (9–10 vs 13–14 µm); in the nature of the spicules (20–23 µm long with regularly arcuate ventral arm without hump vs 50–57 µm long with prominent hump), median piece with blunt end in head region (vs simple, ending with a very sharply pointed projection); shorter and slender lateral guiding pieces, slightly curved dorsally (5–7 µm vs 14–16 µm long and robust, slightly bent ventrally in middle) and differently shaped tail (obtusely rounded vs hemispherical).

From A. siddiqii it differs in the shape of the lip region (outer and inner lip depression indistinct vs inner lips rounded amalgamated and outer lips demarcated by a depression); posterior vulva position (V = 53–56 vs 52–52.5); in shape and size of the vagina (15–19 µm long and slightly bent posteriorly with a constriction in the middle vs 25–28 µm long and highly bent posteriad, regularly narrowing toward the uterus); in the shape and size of spicules (vs 32 µm long, simple arcuate, with proximal slender part about ⅓ of total spicule length with slightly curved ends), in the nature of the median pieces (vs ending with a long sharp pointed projection) and in the shape and size of the lateral guiding pieces (5–7 µm, slightly curved dorsally vs 10 µm long, slightly bent ventrally).

From A. noreasum , it differs in the shape of the vagina (vagina slightly bent posteriad vs strongly bent posteriad); mainly in the shape and size of spicules (vs 30–36 µm with proximal slender part about 2/ 5 of the total spicule length, and distal part comparatively robust and slightly arcuate), in the shape of the median piece (vs expanded in the middle and ending in a long pointed projection in slender part of spicules); in the shape and size of the lateral guiding pieces (5–7 µm long, slightly curved dorsally vs 8–13 µm long, almost straight) and the cuticle thickening on the tail terminus (3–5 vs 6–8 µm).

Figures

Fig. 7. Axonchium microspiculum sp. nov. A, C–H, K. Holotype, ♀ (slide 1). B, I–J. Paratype 4, ♂ (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. Female genital system. H. Vulva. I. Male posterior region. J. Spicule and lateral guiding piece. K. Female posterior end.

Fig. 8. Axonchium microspiculum sp. nov. (LM photographs). A–G, L. Holotype, ♀ (slide 1). H– K. Paratype 4, ♂ (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. Male testes. I. Ventromedian supplements. J. Male posterior end. K. Arrows showing lateral guiding piece and first ventromedian supplement. L. Female posterior end. Scale bars: A–G, I–L = 10 µm; H = 20 µm.