Dorylaimoides teres 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 : 313-317

Dorylaimoides teres Thorne and Swanger, 1936

( Figures 1 and 2 ; Table 1 )

Description

Female. Medium-sized nematodes, curved ventrad upon fixation; tapering gradually towards both extremities but more so towards the anterior end. Cuticle with two distinct layers, 1.5 μm thick at anterior region, 2.0 μm at midbody and 3.0–4.0 μm at tail. Outer cuticle thin, with transverse striations; inner layer thick, finely striated. Lateral chords 7.0– 10 μm at midbody, occupying about one-fifth to one-fourth (19–24%) of corresponding body diameter. Lateral, dorsal and ventral body pores indistinct. Lip region cap-like, offset by slight depression, 2.0–2.5 times as wide as high or about one-third of the body diameter at neck base. Under SEM ( Figure 2 (a) and (b)), lips rounded, low, amalgamated; labial and cephalic papillae button-like, slightly protruding over the lip surface; oral aperture slit-like. Amphids large, cup-shaped, with large slit-like aperture ( Figure 2 (b)), occupying an area about one-half to three-fifths as wide as lip region diameter. Odontostyle long, asymmetrical, 1.2–1.3 times as long as the lip region diameter; ventral arm 7.5–8.5 μm long; dorsal arm 9.0–9.5 μm long, its aperture about one-fourth of the odontostyle length. Odontophore arcuate, about 1.2–1.4 times the odontostyle length. Guiding ring simple, refractive, at 0.8–0.9 times the lip region diameter from anterior end. Pharynx consisting of a slender and slightly muscular anterior part, expanding gradually into a short, cylindrical basal bulb, 2.9–4.2 times as long as wide, 1.6–2.0 times corresponding body diameter, occupying about 24–27% of total neck length. Pharyngeal gland nuclei hardly visible. Nerve ring located at 46–48% 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 92– 169 μm (anterior) and 106–196 μm (posterior) long; oocytes arranged in a single row except near tip. Oviduct joining the ovary subterminally, measuring 57–87 μm (anterior) and 69–106 μm (posterior), consisting of a slender distal portion and a well-developed pars dilatata. Oviduct-uterus junction marked by well-developed sphincter. Uterus long and tubular, measuring 71–130 μm (anterior) and 64–87 μm (posterior). Sperm cells present throughout the genital tract, rarely absent. Vagina cylindrical, extending inwards, length 19.5–20.5 μm or about one-half to three-fifths (48–58%) of midbody diameter; pars proximalis vaginae 11–15 × 9–11 μm, encircled by circular muscles; pars distalis vaginae 5.0–6.0 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 6.0–7.1 and rectum 1.0–1.2 times anal body diameter long. Tail short, cylindrical, convex-conoid to rounded, 1.1–1.2 times anal body diameter long, with a pair of caudal pores on each side.

Male. General morphology similar to that of female but body slightly shorter than female, 1.3–1.4 mm long, posterior region being more ventrally curved. Genital system diorchic, testes opposed, sperm cells spindle-shaped, 5.0–6.0 μm long. In addition to adcloacal pair, situated at 6.0–7.0 µm from cloacal aperture, there are four to six irregularly spaced ventromedian supplements, first ventromedian supplement located within the range of spicules, 23–25 μm from adcloacal pair. Spicules typically dorylaimoid, curved ventrad, relatively robust, 5.0–6.0 times as long as wide and 1.5 times as long as cloacal body diameter, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 128–132°, head occupying 15–18% of total spicules’ length, median pieces 15–16 times as long as wide, occupying 28–33% of the spicules’ maximum width, reaching the spicules’ tip, posterior end 3.5–4.0 μm wide. Lateral guiding pieces distinct, rod-like, about 4.7–6.0 times as long as wide or about onefourth of the spicules’ length. Prerectum 7.5–8.5 and rectum 1.4–1.6 times cloacal body diameter long. Tail short, cylindrical, convex-conoid to rounded, 1.0–1.1 times the cloacal body diameter long, with a pair of caudal pores on each side.

Habitat and locality. Soil sample collected around the roots of grasses (unidentified) from Thirtha, Shivamoga district, Karnataka State, India; coordinates 14.123389°N, 75.056611°E .

Remarks. Thorne and Swanger (1936) proposed the genus Dorylaimoides with D. teres as its type species from the USA. Altherr (1953) and Thorne (1974) reported it from Switzerland and the USA, respectively. Goseco, Ferris and Ferris (1976), in their revision of the genus Dorylaimoides , made a detailed study of the type population as well as two other populations from the USA (Missouri and Arizona). They (1976) differentiated this species from D. indicus Jairajpuri, 1965 by the presence of a more conoid tail, from D. parateres Siddiqi, 1964 by having a longer pharyngeal bulb, and from D. thecolaimus Heyns, 1963 by a more anterior vulva position. Peralta and Peña-Santiago (1995) also redescribed this species, with four different populations from Spain. The morphometrics of the present population conforms well with the type population except in having a longer ventral arm of the odontostyle (7.5–8.5 vs 6 μm) and a slightly longer tail (29– 32 vs 21–29 μm). The present population conforms well with Altherr’s (1953) population but slightly differs from Thorne’s (1974) population in having higher b (6.9–7.8 vs 5.6–5.9) and c (47–55 vs 31–43) ratios. The present specimens also conform well with Goseco et al.’s (1976) specimens; however, they slightly differ from the Spanish population described by Peralta and Peña-Santiago (1995) in having a long and slender body (L = 1.5–1.6 vs 1.1–1.4 mm, a = 39–43 vs 29–39) and differently shaped tail (rounded to convex-conoid, its terminal part not dorsally bent, vs rounded to convex-conoid, sometimes terminal part bent dorsally). These slight variations should be considered intraspecific as well as geographical variability. This species is reported here for the first time from India.

Figures

Figure 1. Dorylaimoides teres Thorne and Swanger, 1936 (LM photographs). (a, b) Anterior region; (c) anterior region showing amphid; (d) pharyngeal region;(e) pharyngeal expansion;(f) expanded part of pharynx; (g, h) female genital system; (i) vulval region; (j) female posterior region; (k) female posterior end; (l, m) male posterior end. Scale bars: a–c, e, f, i, k–m = 10 μm; d, g, h, j = 20 μm.

Figure 2. Dorylaimoides teres Thorne and Swanger, 1936 (SEM photographs). (a, b) en face view showing labial papillae and amphid aperture; (c) vulval region; (d) male posterior region (arrows showing ventromedian supplements, adcloacal pair and cloacal aperture); (e) female posterior end, with arrow showing anal opening. Scale bars: a, b = 2 μm; c–e = 10 μm.