Axonchium tropicum, 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 : 37-41

Axonchium tropicum sp. nov.

urn:lsid:zoobank.org:act:84CBC84A-16B6-424A-B6C9-635525595B0A

Figs 13–14 , Table 9

Diagnosis

Axonchium tropicum sp. nov. is characterized by having a 1.7–2.0 mm long body; lip region offset; amphids stirrup-shaped; odontostyle large, 11–12 µm long, about equal to the odontophore; two parts of the pharynx separated by deep constriction; anterior uterine sac 2.3–4.0 times the mid-body diameter long; vagina slightly bent posteriad, tail broadly rounded; spicules 40 µm or 1.1 times the cloacal body diameter long; lateral guiding pieces 14 µm long with bifurcated distal end; four widely spaced ventromedian supplements, beginning above the range of spicules.

Etymology

The new species is named A. tropicum because of its distribution in tropical rain forests.

Material examined

Holotype INDIA • ♀; Kerala State, Kasaragod District, Ranipuram National Park ; 12°25ʹ16.01ʺ N, 75°21ʹ0.27ʺ E; 10–15 cm depth; 7 Nov. 2016; roots of plants (unidentified); slide reference number AMU/ZD/ NC/ Axonchium tropicum /1.

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

Type habitat and locality

Soil samples collected around the roots of plants (unidentified) from Ranipuram National Park, Kasaragod District, Kerala State, India.

Description

Female

Body slightly 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, 5–7 µm on tail tip in females and 3 µm in male. Lateral chords 5–7 µm wide, about 1/ 8 (11–12%) of mid-body diameter; glandular bodies poorly developed, 28–42 in number: 14 in pharyngeal region, 3–5 from pharynx base to vulva, 22–23 from vulva to anal region and 1–2 in caudal region. Lateral, dorsal and ventral body pores indistinct. Lip region rounded, offset by deep constriction, 2.0–2.5 times as wide as high or about 1/ 5 (17–21%) of body diameter at neck base. Lips separate, outer and inner portions demarcated by shallow depression. Amphid fovea stirrup-shaped, their aperture occupying about 0.6–0.7 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, 5–6 times as long as wide, or 1.2 times lip region diameter long, its aperture occupying about ⅓ of its length. Odontophore simple, rodlike, 1.0–1.2 times as long as odontostyle. Nerve ring encircling anterior slender part of pharynx at 18–19% 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 13–17 times as long as wide, or 8–10 times as long as body diameter at neck base, and occupying about 3/ 5 to slightly more than ⅔ (63–71%) of total neck length, enclosed in a thick muscular sheath with straight bands. Only dorsal pharyngeal gland and its orifice visible: DO = 33.8–38.4; DN = 34.2–39; DO–DN = 0.4–0.5. Cardia tongue-like, 1.8–2.3 times as long as wide, occupying about ⅓ to ½ (37–47%) of corresponding body diameter.

Genital system mono-opisthodelphic. Anterior genital branch represented by simple uterine sac with a slightly proximal constriction, measuring 136–168 µm or 2.3–4.0 times mid-body diameter long, and occupying 6.8–9.6% of body length; mostly containing spindle-shaped sperms. Posterior branch well developed; ovary reflexed, not reaching oviduct-uterus junction, measuring 82–105 µm long with squamous shaped oocytes arranged in a single row except near tip; oviduct joining ovary subterminally, measuring 85–105 µm or 1.6–2.4 times mid-body diameter long, consisting of a long slender part with prismatic cells and a well developed pars dilatata with distinct lumen; sphincter present at oviductuterus junction; uterus 71–126 µm or 1.6–2.1 times mid-body diameter long, appearing strongly convoluted, and differentiated into a large proximal region with wide lumen, a narrow intermediate region, and a short spherical distal pars dilatata with distinct lumen; vagina slightly bent posteriad, extending inwards about ½ (42–50%) of corresponding body diameter; pars proximalis vaginae longer than wide, 10–12 × 3–4 µm, surrounded by circular musculature; pars refringens vaginae absent; pars distalis vaginae 8–15 µm. Prerectum 4.5–9.3 and rectum 1.1–1.4 times anal body diameter long. Tail short, broadly rounded. 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 spindle-shaped, measuring 4–6 × 2 µm. In addition to adcloacal pair, located at 10 µm from cloacal aperture, four irregularly spaced ventromedian supplements, beginning just in front of proximal end of spicules; first located at 43 µm from adcloacal pair, second at 23 µm from the first, third at 51 µm from second and fourth at 25 µm from third ventromedian supplement. Copulatory muscles conspicuous, beginning from level of middle of spicules and continuing until level of last supplement. Spicules well developed, arcuate, unusually wide with blunt distal end; total length along arc 1.1 times as long as chord, 5 times maximum width or 1.3 times body diameter at cloacal aperture. Curvature about 135°. Dorsal contour regularly convex, except distal end bent ventrally at right angle; ventral contour concave, bearing a prominent hump, located at 42% of spicule total length from its anterior end; head narrow, slightly curved, and occupying about 15% of spicule length; median piece simple, 7 times as long as wide, and occupying about 62% of spicule maximum width; posterior end 6 µm wide. Lateral guiding pieces almost straight, rod-like, with bifurcated distal ends; about 7.0 times as long as wide, and occupying about ⅓ (35%) of total spicule length. Prerectum long, 8.4 and rectum 1.5 times cloacal body diameter long. Tail similar to that of female. Caudal pores three on each side.

Taxonomic remarks

The new species comes close to A. shamimi Baqri & Khera, 1976 , A. elegans Jairajpuri, 1964 and A. neoeletum Rahman, Jairajpuri & Ahmad, 1985 on the basis of its body size, anterior uterine sac size, spicule and lateral guiding piece sizes, and arrangements of ventromedian supplements, but it differs from the former in having a longer body (L = 1.7–2.0 vs 1.3–1.6 mm), longer odontostyle (11– 12 vs 8–9 µm); longer prerectum (8.4 vs 6–7 times cloacal body diameter long); smaller number of ventromedian supplements (4 vs 6–7); and in the arrangement of ventromedian supplements (beginning just in front of proximal end of spicules vs posterior to the proximal end of spicules), slightly longer spicules (40 vs 36–39 µm long).

It differs from A. elegans in having a wider lip region (9–10 vs 6–8 µm); longer odontostyle (11–12 vs 7–9 µm); in the shape of the spicules (vs unusually wide with blunt distal end); shape of lateral guiding pieces (bifurcated distal end vs with thickened distal end) and in shape of tail (broadly rounded vs obtusely rounded).

It differs from A. neoeletum in having a longer body (L = 1.7–2.0 vs 1.4–1.6 mm); comparatively wider lip region (9–10 vs 7–9 µm); longer odontostyle (11–12 vs 8–9 µm); smaller number of ventromedian supplements (4 vs 4–8); comparatively slender spicules (five times the maximum width vs 3.5–4.6 times the maximum width) and in shape of lateral guiding pieces (rod-like, almost straight with bifurcated distal end vs slightly curved in proximal region).

Figures

Fig. 13. Axonchium tropicum sp. nov. A, D–H, L. Holotype, ♀ (AMU/ZD/Axonchium tropicum sp. nov. /1). B, I–K. Paratype 1, ♂ (slide 2). C. Paratype 2, ♀ (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 pieces. L. Female posterior end.

Fig. 14. Axonchium tropicum sp. nov. (LM photographs). A. Paratype 2, ♀ (slide 2). B–G, L. Holotype, ♀ (AMU/ZD/Axonchium tropicum sp. nov. /1). H–K. Paratype 1, ♂ (slide 2). A. Anterior region. B. Anterior end showing amphid. C. Junction between two parts of pharynx. D. Cardia. E. Vulva and vagina. F–G. Genital branches. H. Ventromedian supplements. I. Lateral guiding pieces. J. Male posterior region and spicule. K. Spicule with arrow indicating its distal end. L. Female posterior region. Scale bars: A–E, I–L =10 µm; F–H = 20 µm.