Dorylaimoides brevicaudatus, Islam & Ahmad, 2022

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 : 335-339

Dorylaimoides brevicaudatus sp. nov.

( Figures 8 and 9 ; Table 7 )

Description

Female. Slender nematode of small to medium size, 0.99–1.1 mm long, slightly ventrally curved to open C-shaped upon fixation; tapering gradually towards both extremities. Cuticle with two distinct layers, 1.5–2.0 μm thick at anterior to midbody and 2.0–3.0 μm at tail. Outer cuticle thin, with fine transverse striations; inner layer thick, distinctly striated. Lateral chords 5.0–7.0 μm at midbody, occupying about onefifth (17–21%) of corresponding body diameter. Lateral, ventral and dorsal body pores indistinct. Lip region cap-like, narrow, almost continuous or offset by slight depression, 1.5–1.8 times as wide as high or about one-fourth of the body diameter at neck base. Lips rounded, amalgamated, inner part slightly raised. Amphids cupshaped, their aperture occupying about two-thirds to three-fourths of lip region diameter. Stoma a truncate cone. Odontostyle short, asymmetrical, 0.85–1.1 times the lip region diameter long, ventral arm 5.0–5.5 µm, dorsal arm 6.0–6.5 µm, its aperture small, about one-seventh to one-fifth of the odontostyle length. Odontophore arcuate, about 1.3–1.6 times the odontostyle length. Guiding ring simple, refractive, at 0.6–0.7 times lip region diameter from anterior end. Pharynx consisting of a slender and slightly muscular anterior part, expanding gradually, into a short, cylindrical basal bulb, 3.2–4.2 times as long as wide, 1.4–1.7 times corresponding body diameter, occupying about 24–28% of total neck length. Pharyngeal gland nuclei visible. Nerve ring at 43–53% of neck length from anterior end. Cardia rounded to conoid, about one-fourth to one-third of the corresponding body diameter long. Genital system didelphic-amphidelphic. Ovaries reflexed, measuring 69– 89 μm (anterior) and 68–89 μm (posterior) long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 53–88 μm (anterior) and 56–75 μm (posterior), consisting of a slender distal part and a welldeveloped pars dilatata. Oviduct-uterus junction marked by well-developed sphincter. Uterus short and tubular, measuring 39–81 μm (anterior) and 39–70 μm (posterior). Sperm cells present throughout the genital tract. Vagina cylindrical, extending inwards, 14.0–17.0 μm or about one-half to three-fifths (47–59%) of midbody diameter; pars proximalis vaginae 9.0–11.5 × 7.0–9.0 μm, encircled by circular muscles; pars distalis vaginae short, 3.0–4.0 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 2.0–4.0 and rectum 0.9–1.0 times anal body diameter long. Tail short, cylindrical, convex-conoid with rounded terminus, 0.7–0.8 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, 6.0–8.0 μm long. In addition to adcloacal pair, situated at 7.0–9.0 µm from cloacal aperture, there are five to eight irregularly spaced ventromedian supplements, first ventromedian beginning at level with the head of spicules. Spicules typically dorylaimoid, curved ventrad, slender, 5.4–7.7 times as long as wide and 1.4–1.7 times as long as cloacal body diameter, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 128–135°, head occupying 9–10% of total spicules’ length, median pieces 16–20 times as long as wide, occupying about 30–37% of the spicules’ maximum width, reaching the spicules’ tip, posterior end 2.0–2.5 μm wide. Lateral guiding pieces distinct, rod-like, about 4.6–5.3 times as long as wide or about onefourth of the spicules’ length. Prerectum 2.9–5.1 and rectum 1.3–1.7 cloacal body diameter long. Tail short, cylindrical, convex-conoid with rounded terminus, 0.8–0.9 times the cloacal body diameter, with a pair of distinct caudal pores on each side.

Type habitat and locality

Soil around the roots of grasses (unidentified) from Verna , South Goa district, Goa State, India; coordinates 15.353583°N, 73.922278°E.

Type specimens

Holotype female on slide Dorylaimoides brevicaudatus sp. nov. /1; paratype females on slides Dorylaimoides brevicaudatus sp. nov. /2–4; paratype males on slides Dorylaimoides brevicaudatus sp. nov. /5–7; deposited with nematode collection of the Department of Zoology, Aligarh Muslim University, India.

Etymology

The new species is named Dorylaimoides brevicaudatus because of its short tail.

Diagnosis and relationships

Dorylaimoides brevicaudatus sp. nov. is characterised by having a slender body, 0.99– 1.1 mm long; lip region cap-like, almost continuous or offset by slight depression; odontostyle 7.5–8.5 μm, ventral arm 5.0–5.5 µm, dorsal arm 6.0–6.5 µm; odontophore 10.5–12.5 μm long, arcuate; total stylet length 18.5–20.0 μm; pharynx slender with slightly muscular anterior part, expanding gradually into a short, cylindrical basal bulb occupying about 25–30% of total neck length; female genital system didelphic-amphidelphic; tail short, convex-conoid with rounded terminus, males with 24.5–30 µm long spicules, lateral guiding pieces and 5–7 irregularly spaced ventromedian supplements.

In the presence of short expanded part of pharynx and short, rounded to conoid tail, the new species resembles D. cameroonensis Ahmad et al., 2003 and D. parateres Siddiqi, 1964 but differs from the former in having a long and slender body (L = 0.91–1.1 vs 0.76– 0.87 mm, a = 33–39 vs 25–29), narrower lip region (7.0–8.0 vs 9.0–11 μm), shorter odontostyle (7.5–8.5 vs 10–11 μm) and higher b (5.7–6.9 vs 4.6–5.5) and c (64–79 vs 43– 60) ratios.

The new species differs from D. parateres in having a shorter body (L = 0.9–1.1 vs 1.2– 1.6 mm), slightly posterior vulva position (V = 47–51 vs 39–48), lower c’ ratio (0.7–0.9 vs 1.0–1.5), shorter and differently shaped tail (15–17 vs 27–29 μm long, convex-conoid to rounded vs rounded to hemispheroid) and smaller spicules (24.5–30 vs 35–36 μm).

In the presence of amphidelphic gonads and a short tail, the new species also resembles D. indicus Jairajpuri, 1965 and D. teres Thorne and Swanger, 1936 , but differs from the former in having a shorter body (L = 0.9–1.1 vs 1.1–1.8 mm), shorter pharyngeal expansion (41–50 vs 64 μm or 24–30 vs 31% of total neck length), slightly posterior vulva position (V = 47–51 vs 39–47), shorter tail (15–17 vs 18–26 μm) and smaller spicules (24.5– 30 vs 38 μm).

The new species differs from D. teres in having a comparatively shorter body (0.9–1.1 vs 1.1–1.6 mm), differently shaped and narrower lip region (conoid vs rounded, 7.0–8.0 vs 9.0–10 μm), shorter pharyngeal expansion (41–50 vs 51–63 μm), slightly posterior vulva position (V = 47–51 vs 40–48), shorter tail (15–17 vs 21–30 μm) and smaller spicules (24.5– 30 vs 35–38 μm).

Figures

Figure 8. Dorylaimoides brevicaudatus sp. nov. (a) Entire female; (b) entire male; (c) anterior region; (d) anterior region showing amphid; (e) pharyngeal region; (f) pharyngeal bulb; (g) female genital system; (h) female posterior region; (i, j) male posterior region.

Figure 9. Dorylaimoides brevicaudatus sp. nov. (LM photographs). (a, b) Anterior region; (c) anterior region showing amphid; (d) pharyngeal region; (e) expanded part of pharynx; (f) female genital system; (g) vulval region; (h) female posterior region; (i, j) female posterior end; (k, l) male posterior end. Scale bars: a–c, e, g–l = 10 μm; d, f = 20 μm.