Dorylaimoides parvus Thorne and Swanger, 1936

Islam, Md Niraul & Ahmad, Wasim, 2022, Description of two new and six known amphidelphic species of the genus Dorylaimoides Thorne and Swanger, 1936 (Nematoda: Dorylaimida: Tylencholaimoidea) from the Tropical Rainforest, Western Ghats, India, Journal of Natural History 56 (5 - 8), pp. 311-347 : 321-324

Dorylaimoides parvus Thorne and Swanger, 1936

( Figure 4 ; Table 3 )

Description

Female. Small, slender nematode, slightly ventrally curved upon fixation; body cylindrical, tapering gradually towards the anterior end, posteriorly narrowing into an elongate to long filiform tail. Cuticle with two distinct layers, 1.0–1.5 µm thick at anterior region, 1.5–2.0 µm at midbody and 3.0–5.0 μm at tail. Outer cuticle thin, smooth; inner layer thick, finely striated. Lateral chords 4.0–6.0 µm at midbody, occupying about one-seventh to one-fifth (13–19%) of corresponding body diameter. Lateral, ventral and dorsal body pores indistinct. Lip region cap-like, slightly offset by depression, 1.7–2.2 times as wide as high or about one-fourth of the body diameter at neck base. Lips, rounded, amalgamated. Amphids cup-shaped, their aperture occupying an area about two-thirds to fourfifths as wide as lip region diameter. Odontostyle long, slender, asymmetrical, 1.1–1.5 times the lip region diameter long, ventral arm 6.0–6.5 µm, dorsal arm 7.0–8.5 µm, its aperture about one-fourth of the odontostyle length. Odontophore arcuate, about 1.2–1.7 times the odontostyle length. Guiding ring simple, refractive, at 0.8–1.0 times the lip region diameter from anterior end. Pharynx consisting of a slender and slightly muscular anterior part, expanding abruptly into a short, cylindrical basal bulb, separated by slight constriction, 3.3–4.3 times as long as wide, 1.6–1.8 times corresponding body diameter long, occupying about 23–28% of total neck length. Pharyngeal gland nuclei visible. Nerve ring located at 46–51% of neck length from anterior end. Cardia short, rounded to conoid, about one-sixth to one-fourth of the corresponding body diameter long. Genital system didelphic-amphidelphic. Ovaries reflexed, measuring 39–85 μm (anterior) and 41–93 μm (posterior) long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 38–78 μm (anterior) and 40–83 μm (posterior), consisting of a slender distal part and a well-developed pars dilatata. Oviduct-uterus junction marked by well-developed sphincter. Uterus slightly long and tubular, measuring 45–63 μm (anterior) and 41–61 μm (posterior). Sperm cells usually present throughout the genital tract. Vagina cylindrical, extending inwards, 14–18 μm or less than one-half to three-fifths (45–63%) of midbody diameter; pars proximalis vaginae 9.0–12.0 × 6.0–10 μm, its wall encircled by circular muscles; pars distalis vaginae long, 6.0–8.0 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 3.7–6.7 and rectum 1.0–1.5 times anal body diameter long. Tail elongated to long filiform with rounded tip, tapering gradually, its distal part bent dorsally, 5.6–6.9 times anal body diameter long, with a pair of caudal pores on each side.

Male. General morphology similar to that of female except for posterior region being more ventrally curved. Genital system diorchic, testes opposed, sperm cells spindleshaped, 5.0–6.0 μm long. In addition to adcloacal pair, situated at 7.0–9.0 µm from cloacal aperture, there are three to four irregularly spaced ventromedian supplements, located outside the range of spicules; first ventromedian supplement located 25–29 μm from adcloacal pair. Spicules typically dorylaimoid, curved ventrad, relatively slender, 5.8–7.3 times as long as wide and 1.3–1.6 times as long as cloacal body diameter, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 130–136°, head occupying 12–16% of total spicules’ length, median pieces 12.5–16.5 times as long as wide, occupying 37–50% of the spicules’ maximum width, reaching the spicules’ tip, posterior end 2.0–2.5 μm wide. Lateral guiding pieces distinct, rod-like, 4.7–6.0 times as long as wide or about one-fourth of the spicules’ length. Prerectum 5.0–6.6 and rectum 1.3–1.6 cloacal body diameter long. Tail elongated to long filiform with rounded tip, tapering gradually, its distal part bent dorsally, 5.1–5.8 times cloacal body diameter long, with a pair of caudal pores on each side.

Habitat and locality. Soil sample collected around the roots of forest trees (unidentified) from Silent Valley National Park , Mukkali, Palakkad district, Kerala State, India; coordinates; 11.063778°N, 76.538167°E .

Remarks. Thorne and Swanger (1936) described Dorylaimoides parvus based on eight females and three males from Brazil. Loof (1964) redescribed this species from Venezuela. Goseco et al. (1976), in their revision of the genus Dorylaimoides , restudied the type specimens as well as the Venezuelan specimens. Jana and Baqri (1981) reported it from India. The morphometrics of the present population conforms well with the type population except in having a slightly less slender body (a = 32–37 vs 37–58) and lower b (5.3–6.1 vs 6.1–7.5) and c (7.9–9.7 vs 10–13) ratios. The present specimens also conform well with the Venezuela specimens except in having smaller spicules (28–32 vs 34–36 µm). The present population also conforms well with the Indian population except in having a slightly shorter body (L = 0.9–1.2 vs 1.2–1.5 mm) and lower b (5.3–6.1 vs 6.7–8.0) and c (7.9–9.7 vs 11–14) ratios. These differences are considered intraspecific variability.

In the presence of an elongated tail, Dorylaimoides parvus resembles D. elaboratus Siddiqi, 1965 and D. paulbuchneri Meyl, 1956 , but it differs from the former in having differently shaped spicules (slender, slightly curved ventrally vs robust, more curved ventrally) and first ventromedian supplements located beyond the range of the spicules (vs first ventromedian supplements located within the range of the spicules).

From D. paulbuchneri , it differs in having labial papillae indistinct (vs distinct); differently shaped odontostyle (slender vs robust) and differently shaped spicules (slender, slightly curved ventrally vs robust, more ventrally curved).

Figures

Figure 4. Dorylaimoides parvus Thorne and Swanger, 1936 (LM photographs). (a, b) Anterior region; (c) anterior region showing amphid; (d) pharyngeal region; (e) expanded part of pharynx; (f, g) female genital system; (h) vulval region; (i) female posterior region; (j, k) female posterior end; (l–n) male posterior region showing spicules. Scale bars: a–c, e–h, j–n = 10 μm; d, i = 20 μm.