Dorylaimoides silvallis, 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 : 340-344

Dorylaimoides silvallis sp. nov.

( Figures 10 and 11 ; Table 8 )

Description

Female. Slender nematode, medium sized, 1.3–1.4 mm long, slightly ventrally curved upon fixation; body tapering gradually towards anterior end, posteriorly narrowing to form a 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 3.5–4.0 μm at tail. Outer cuticle thick, smooth; inner layer thick, finely striated. Lateral chords 5.0–6.0 μm at midbody, occupying about oneseventh to one sixth (13–18%) of corresponding body diameter. Lateral, ventral and dorsal body pores indistinct. Lip region cap-like, continuous with body, 2.0–2.3 times as wide as high or about one-fourth of the body diameter at neck base. Lips rounded, amalgamated, inner part slightly raised. Amphids cup-shaped, duplex, their aperture occupying about three-fifths to two-thirds of lip region diameter. Odontostyle long, slender, asymmetrical, 1.4–1.7 times the lip region diameter long, ventral arm 8.5–9.0 μm, dorsal arm 9.5– 10.5 μm, its aperture about one-fourth to one third of the odontostyle length. Odontophore arcuate, about 1.1–1.3 times the odontostyle length. Guiding ring simple, refractive, at 0.8–0.9 times 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 a depression, 4.1–5.3 times as long as wide or 1.7–2.4 times corresponding body diameter, occupying about 31–35% of total neck length. Pharyngeal gland nuclei visible. Nerve ring located at 44–47% of neck length from anterior region. Cardia short, conoid, about one-seventh to one-third of the corresponding body diameter long. Genital system didelphic-amphidelphic. Ovaries reflexed, measuring 49–79 μm (anterior) and 50–99 μm (posterior) long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 48–82 μm (anterior) and 49– 88 μm (posterior), consisting of a slender part and a well-developed pars dilatata. Oviductuterus junction marked by well-developed sphincter. Uterus long and tubular, filled with sperm cells, measuring 48–78 μm (anterior) and 42–78 μm (posterior). Vagina cylindrical, extending inwards, 17.5–21.5 μm or about two-fifths to one-half (45–54%) of midbody diameter; pars proximalis vaginae 9.0–13 × 8.0–10 μm, encircled by circular muscles; pars distalis vaginae 3.0–4.0 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 6.2–8.6 and rectum 1.1–1.3 times anal body diameter long. Tail long filiform with finely rounded terminus, tapering gradually, its distal part always curved ventrally, 8.6–9.7 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 7.0–10 µm from cloacal aperture, there are four to five irregularly spaced ventromedian supplements, located outside the range of spicules; first ventromedian supplement located 27–29 μm from adcloacal pair. Spicules typically dorylaimoid, curved ventrad, relatively robust, 4.6–5.3 times as long as wide and 1.2–1.4 times as long as body diameter at level of cloacal aperture, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 130–133°, head occupying 14–18% of total spicules’ length, median pieces 12.7–14.0 times as long as wide, occupying 28–33% of the spicules’ maximum width, reaching the spicules’ tip, posterior end 3.0 μm wide. Lateral guiding pieces distinct, rod-like, 6.0–6.7 times as long as wide or about onefourth of the spicules’ length. Prerectum 5.0–7.9 and rectum 1.3–1.6 times anal body diameter long. Tail long filiform with finely rounded terminus, tapering gradually, its distal part curved ventrally, 7.2–8.8 times anal body diameter long, with a pair of caudal pores on each side.

Type 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.

Type specimens

Holotype female on slide Dorylaimoides silvallis sp. nov. / 1; paratype females on slides Dorylaimoides silvallis sp. nov. / 2–4; paratype males on slide Dorylaimoides silvallis sp. nov. / 5 & 6; deposited with nematode collection of the Department of Zoology, Aligarh Muslim University, India.

Etymology

The new species is named Dorylaimoides silvallis after its type locality, Silent Valley National Park .

Diagnosis and relationships

Dorylaimoides sivallis sp. nov. is characterised by having a slender body, 1.3–1.4 mm long; lip region continuous; odontostyle 12.5–13.5 μm long, ventral arm 8.5–9.0 µm, dorsal arm 9.5–10.5 µm; odontophore arcuate, 14.5–16.5 μm long, total stylet length 27.5–29.5 μm; pharynx slender with slightly muscular anterior part, expanding abruptly into a short, cylindrical basal bulb occupying about 31–35% of total neck length; female genital system didelphic-amphidelphic; tail long filiform with ventrally bent tip, 8.6–9.7 times anal body diameter long, males with 31–33 µm long spicules, lateral guiding pieces and 4–5 irregularly spaced ventromedian supplements.

In its medium-sized body and long filiform tail the new species resembles D. malabaricus Ahmad and Jairajpuri, 1982 and D. filicaudatus Jana and Baqri, 1981 , but it differs from the former in having differently shaped amphids (duplex, cup-shaped vs simple, cup-shaped), a slightly longer odontostyle (12.5–13.5 vs 8.0–11 µm), longer pharyngeal expansion (66–78 vs 47–58 µm or 31–35 vs 23–27% of total neck length), lower c’ ratio (8.6–9.7 vs 10.1–13.7), differently shaped tail (tail filiform, its tip always bent ventrally vs tail very long filiform, its tip bent dorsally) and slightly smaller spicules (31–33 vs 34–36 µm).

The new species differs from D. filicaudatus in having duplex amphids (vs simple), a longer odontostyle (ventral arm 8.5–9.5 vs 4.0–5.0, dorsal arm 9.5–10.5 vs 6.0–7.0 µm), longer pharyngeal expansion (66–78 vs 50 µm or 31–35 vs 25–29% of total neck length), higher c (6.2–7.1 vs 4.1–5.5) and lower c’ (8.6–9.7 vs 13–15) ratios, shorter tail (200–215 vs 214–251 µm) and slightly longer spicules (31–33 vs 24–29 µm).

The new species also resembles D. elaborates Siddiqi, 1965 and D. lepidus Timm, 1964 , but differs from the former in having a longer body (L = 1.3–1.4 vs 0.9–1.2 mm), amphids duplex (vs simple), longer odontostyle (12.5–13.5 vs 10–11 µm), lower c (6.2–7.1 vs 7.0– 8.0) and higher c’ (8.6–9.7 vs 6.0–8.0) ratios, longer tail (200–215 vs 145–150 µm), slightly longer spicules (31–33 vs 28–-31 µm) and differently shaped tail, its distal part always ventrally bent (vs dorsally).

The new species differs from D. lepidus in having a narrower lip region (8.0–9.0 vs 11 µm), amphids duplex (vs simple), longer odontostyle (12.5–13.5 vs 8 µm) and odontophore (14.5–16.5 vs 14 µm), lower c (6.2–7.1 vs 9–12) and higher c’ (8.6–9.7 vs 5.5–7.8) ratios, longer tail (200–215 vs 145–150 µm), smaller spicules (31–33 vs 35–42 µm) and fewer ventromedian supplements (4–5 vs 9–11).

Figures

Figure 10. Dorylaimoides silvallis sp. nov. (a) Entire female; (b) entire male; (c, d) anterior region; (e) anterior region showing amphid; (f) expanded part of pharynx; (g) pharyngeal region; (h) female genital system; (i) female posterior region; (j, k) male posterior region.

Figure 11. Dorylaimoides silvallis sp. nov. (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, i) vulval region; (j, k) female posterior end; (l) male posterior region; (m–o) male posterior region showing spicules. Scale bars: a–c, e–i, m–o = 10 μm; d, j–l = 20 μm.