Axonchium uniqum, 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 : 42-46

Axonchium uniqum sp. nov.

urn:lsid:zoobank.org:act:7F52E2C7-6005-4727-A949-4EE6C0DC4C51

Figs 15–16 , Table 10

Diagnosis

Axonchium uniqum sp. nov. is characterized by having a 1.7–2.0 mm long body; lip region offset; amphid fovea stirrup-shaped; odontostyle fusiform, 10–11 µm long; both part of the pharynx separated by a deep constriction; basal expanded part of pharynx 71–72% of total neck length; anterior uterine branch 2.5–2.8 times the mid-body diameter long; vulva transverse; vagina expanding gradually in middle; spicules slender, somewhat sickle-shaped, 68 µm long; nine irregularly spaced ventromedian supplements, beginning posterior to the proximal end of the spicules; lateral guiding pieces 20 µm long with bifurcate distal ends; tail broadly conoid.

Etymology

The new species is named A. uniqum because of the unique shape of its spicule.

Material examined

Holotype INDIA • ♀; Maharashtra State, Raigad District, Mahabaleshwar Hill ; 17°55ʹ50.52ʺ N, 73°38ʹ51.72ʺ E; 10–15 cm depth; 12 Apr. 2016; roots of plants (unidentified); slide reference number AMU/ZD/ NC/ Axonchium uniqum /1.

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

Type habitat and locality

Soil samples collected around the roots of plants (unidentified) from Mahabaleshwar Hill, Raigad District, Maharashtra State, India.

Description

Female

Body curved ventrad upon fixation, 1.7–2.0 mm long. Cuticle with fine transverse striations, about 2 µm thick at anterior region, 2–3 µm at mid-body and 8–10 µm on tail tip. Lateral chords 5–13 µm wide, about 1/ 10 to 1/ 5 (8–21%) of mid-body diameter; glandular bodies indistinct. Lateral, dorsal and ventral body pores indistinct. Lip region distinctly offset, 2.2–2.5 times as wide as high, or about 1/ 7 to 1/ 6 (14–16%) of body diameter at neck base. Lips low, bluntly conoid, incompletely separate. Amphid fovea stirrup-shaped, their aperture occupying about 0.7–0.8 times lip region diameter, fusus just opposite to odontophore level. Guiding ring single, at 0.9–1.1 times lip region diameter from anterior end. Odontostyle fusiform, 5.0–5.5 times as long as wide, 1.0–1.1 times longer than lip region diameter, its aperture occupying about ⅓ of its length. Odontophore simple, linear, 1.1–1.4 times as long as odontostyle. Nerve ring encircling anterior slender part of pharynx at 16–19% 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 16.5–16.8 times as long as wide, or 8.2–10.4 times as long as body diameter at neck base, and occupying about ¾ (71–72%) of total neck length, enclosed in a thick muscular sheath with straight bands. Only dorsal pharyngeal gland and its orifice visible: DO = 29; DN = 30; DO–DN = 0.3 (n = 1). Cardia oblong, 1.5–2.5 times as long as wide, occupying about ¼ to ⅓ (23–31%) of corresponding body diameter.

Genital system mono-opisthodelphic. Anterior genital branch represented by simple uterine sac, measuring 147–171 µm or 2.5–2.8 times mid-body diameter long, occupying about 7.2–9.8% of total body length. Posterior branch well developed, its tract always appeared strongly convoluted; ovary reflexed, not reaching oviduct-uterus junction, measuring 63–95 µm long with squamous-shaped oocytes arranged in a single row except near tip; oviduct joining ovary subterminally, 82–90 µm or 1.3–1.5 times mid-body diameter long, consisting of a long slender tubular part with prismatic cells and a wider pars dilatata; oviduct-uterus junction marked by weakly developed sphincter; uterus 75–181 µm or 2.9–3.1 times midbody diameter long, differentiated into a relatively long and convoluted proximal region with wide lumen, and a spherical distal pars dilatata with distinct lumen. Vulva transverse. Vagina straight to slightly bent posterior, extending inwards about three-fifths (57–58%) of corresponding body diameter long; vaginal wall expanding gradually near middle, but not differentiated from body cuticle; pars proximalis vaginae longer than wide, 18–19 × 7–8 µm, surrounded by well developed circular musculature; pars refringens absent; pars distalis 16–17 µm long. Prerectum 3.7–5.6 and rectum 0.9–1.0 times anal body diameter long. Tail broadly conoid with rounded terminus. Caudal pores three 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; sperms ovoid, measuring 3–4 × 1–2 µm. In addition to adcloacal pair, located at 10 µm from cloacal aperture, a series of nine irregularly spaced ventromedian supplements, beginning at 30 µm from adcloacal pair, or posterior to proximal end of spicules. Copulatory muscles conspicuous, beginning from level of middle of spicules and continuing until level of last supplements. Spicules large, comparatively slender, ventrally arcuate, somewhat sickle-shaped in lateral view; total length along arc 1.5 times as long as chord, or 11.3 times maximum width, and about 1.9 times body diameter at cloacal aperture; curvature about 132˚. Dorsal contour irregularly convex, bulge at level of hump, ventral contour concave, bearing a distinct hump, located at 45.6% of spicule total length from its anterior end; head slender with slightly curved tip, occupying about 22.1% of total spicule length; median piece simple, 20.8 times as long as wide, and occupying about 41.6% of spicule maximum width; posterior end about 2 µm wide. Lateral guiding pieces almost straight with bifurcated distal end, about 10 times as long as wide, or about ⅓ (31%) of total spicule length. Prerectum 9.3 and rectum 1.2 times cloacal body diameter long. Tail similar to that of female but having slight depression on ventral side. Caudal pores four on each side.

Taxonomic remarks

In having large and slender spicules and in the arrangement of its ventromedian supplements, the new species comes close to A. sabulum ( Yeates, 1967) sensu Coomans & Yeates 1969 and A. sinclairi Heyns & Furstenberg, 1993 , but it differs from both, in its unique spicular morphology (large, sickleshaped).

It further differs from the former in having a robust body (a = 29–34 vs 43–44); narrower lip region with comparatively low lips (9–10 vs 12 µm wide with comparatively high lips); longer pharynx (b = 2.1– 2.6 vs 3.6–3.7); shorter prerectum (3.7–5.6 vs 9–10 times the anal body diameter long); vagina expanded near the middle (vs not expanded); in shape and size of spicules (69 µm with dorsal contour irregularly convex, bulge at level of hump vs 50–56 µm with simple regularly convex dorsal contour); longer lateral guiding pieces (20 vs 10 µm); in the number and arrangement of ventromedian supplements (9 beginning from posterior to the proximal end of the spicules vs 5–6 starting just opposite to the proximal end of the spicules) and its comparatively longer tail (c = 53–68 vs 81–86).

From A. sinclairi , it differs in the absence of a hemizonid (vs present at level of nerve ring); narrow lip region (9–10 vs 13–15 µm), lips low and incompletely separate (vs well separated from each other with outer and inner portions prominently demarcated by a depression); narrower amphid aperture (6–7 vs 9 µm wide); single guiding ring (vs double); comparatively longer pharynx (b = 2.1–2.6 vs 2.6–3.0); vagina almost straight to slightly posteriorly bent with its walls expanded in the middle (vs posteriad directed and its walls thicker but not expanded); shorter prerectum (3.7–5.6 vs 7 times the anal body diameter long); in shape and size of spicules (vs 78–81 µm long, strongly curved ventrad with simple regularly convex dorsal arm); lateral guiding pieces rod-shaped with bifurcated distal ends (vs simple arcuate without bifurcated distal end) and its longer tail (c = 53–68 vs 80–114).

Figures

Fig. 15. Axonchium uniqum sp. nov. A, C–D, G, L. Holotype, ♀ (AMU/ZD/Axonchium uniqum sp. nov. /1). B, I–K. Paratype 3, ♂ (slide 3). E–F, H. Paratype 2, ♀ (slide 3). A. Entire female. B. Entire male. C.Anterior region.D. Anterior end showing amphid.E. Junction between anterior and posterior expanded part of pharynx. F. Cardia. G. Vulva. H. Female genital system. I. Male posterior end. J. Spicule. K. Lateral guiding piece. L. Female posterior end.

Fig. 16. Axonchium uniqum sp. nov. (LM photographs). A–B, E, L. Holotype, ♀ (AMU/ZD/Axonchium uniqum sp. nov. /1). C–D, F–G. Paratype 2, ♀ (slide 3). H–K. Paratype 3, ♂ (slide 3). A. Anterior region. B. Anterior end showing amphid. C. Junction between anterior and posterior expanded part of the pharynx. D. Cardia. E. Vulva and vagina. F–G. Female genital branches. H. Ventromedian supplements. I. Arrows indicating ventromedian supplements beginning. J. Male posterior end. K. Spicule and lateral guiding piece. L. Female posterior end. Scale bars: A–E, I–L = 10 µm; F–H = 20 µm.