Dorylaimoides arcuicaudatus apud Jana and Baqri, 1981

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 : 331-335

Dorylaimoides arcuicaudatus apud Jana and Baqri, 1981 comb. nov.

( Figure 7 ; Table 6 )

Description

Female. Small nematode, slightly curved ventrad to open C-shaped upon fixation; body cylindrical, tapering gradually towards anterior end, posteriorly narrowing into an elongate ventrally arcuate tail. Cuticle with two distinct layers, 1.0–1.5 μm thick at anterior to midbody and 2.0–2.5 μm at tail. Outer cuticle thin, with fine transverse striations; inner layer thick, distinctly striated. Lateral chords 4.5–5.5 μm at midbody, occupying about one-fifth (17–22%) 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-third of the body diameter at neck base. Lips rounded, amalgamated, with inner part slightly raised. Amphids cup-shaped, their aperture occupying about two-thirds to fourth-fifths of the lip region diameter. Stoma a truncate cone. Odontostyle long, slender, asymmetrical, 1.1–1.4 times the lip region diameter long, ventral arm 5.5–6.0 μm, dorsal arm 7.0–7.5 μm, its aperture about one-fourth of the odontostyle length. Odontophore arcuate, about 1.2–1.5 times the odontostyle length. Guiding ring simple, refractive, at 0.6–0.8 times lip region diameter from anterior end. Pharynx consisting of a slender and slightly muscular anterior part, 3.0–4.1 times as long as wide, 1.4–1.9 times corresponding body diameter, expanding gradually into a short, cylindrical basal bulb, occupying about 26–31% of total neck length. Pharyngeal gland nuclei hardly visible. Nerve ring located at 45–55% of neck length from anterior region. Cardia short, rounded to conoid, about one-sixth to one-fourth of the corresponding body diameter long. Genital system didelphic-amphidelphic. Ovaries reflexed, measuring 37– 54 μm (anterior) and 49–58 μm (posterior) long; oocytes arranged in single row except near tip. Oviduct joining the ovary subterminally, measuring 34–50 μm (anterior) and 33– 56 μm (posterior) long, consisting of a slender distal part and a well-developed pars dilatata. Oviduct-uterus junction marked by well-developed sphincter. Uterus short and tubular, measuring 33–49 μm (anterior) and 40–57 μm (posterior). Sperm cells present throughout the genital tract. Vagina cylindrical, extending inwards, 12–15 μm or about two-fifths to one-half (42–49%) of midbody diameter; pars proximalis vaginae 7.0– 10 × 5.0–7.0 μm, encircled by circular muscles; pars distalis vaginae 4.0–6.0 μm with slightly curved walls; pars refringens absent. Vulva apparently a transverse slit. Prerectum 3.6–5.2 and rectum 0.8–1.2 times anal body diameter long. Tail elongate, conoid ventrally arcuate, 2.0–2.6 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 μm long. In addition to adcloacal pair, situated at 6.0 µm from cloacal aperture, there are two irregularly spaced ventromedian supplements, located outside the range of spicules; first ventromedian supplement located at the level of anterior end of the spicules, 19 μm from adcloacal pair, second at 10 μm from first ventromedian supplement. Spicules typical dorylaimoid, curved ventrad, relatively robust, 4.5 times as long as wide and 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 128°, head occupying 11% of total spicules’ length, median pieces 12 times as long as wide, occupying 40% of the spicules’ maximum width, reaching the spicules’ tip, posterior end 3.0 μm wide. Lateral guiding pieces distinct, rod-like, about 4.3 times as long as wide or one-fourth of the spicules’ length. Prerectum 5.0 and rectum 1.4 cloacal body diameter long. Tail elongate, conoid, ventrally arcuate, 2.0 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 shrubs (unidentified) from Ottakal, Kollam district, Kerala State, India; coordinates 8.988°N, 77.016°E.

Remarks. Baqri (1991) described D. mujtabai from Sikkim, India. The morphometrics of the present specimens conform well with the type specimens except in having a slightly shorter male body (L = 0.64 vs 0.75 mm) and shorter odontophore (12–14 vs 15–16 µm).

Gambhir et al. (1997) described two new species, D. musasus and D. microspicoides , from Manipur, India. Some doubts persist regarding the true identity of these species, because the original description lacks some relevant details. They (l.c.) differentiated D. microspicoides from D. musasus based only on the shorter odontostyle (ventral arm 6.0–7.0 vs 8.0–10 µm, dorsal arm 8.0–9.0 vs 8.0–10 µm) and odontophore (8.0–10 vs 11– 13 µm), smaller b (4.5–4.7 vs 4.9–6.6) and c (19–23 vs 18–20) ratios, shorter rectum (9.0–13 vs 16 µm) and presence of male (vs male absent). According to Gambhir et al. (1997), the two arms of the odontostyle are equal (9.0–10 µm, 8.0–10 µm) in D. musasus , and both arms of the odontostyle are almost the same length in the two species (8.0–10 vs 8.0– 9.0 µm) whereas they differ slightly in the length of the ventral arm (6.0–7.0 vs 8.0–10 µm). These unusual differences create some doubts about the validity of these species, because the dorsal arm is always longer than the ventral arm in all Dorylaimoides species. The figures (figs 1(b) and 2(b) of Gambhir et al. 1997) do not correspond with the morphometric values given in their paper, and there seem to be some errors either in their measurements or in the scales used.

Morphometrically as well as morphologically, D. musasus and D. microspicoides appear very close to D. mujtabai Baqri, 1991 , their morphometric values widely overlapping with the latter. It is interesting to note that these species were not compared with D. mujtabai in the original description. There is every possibility that they are conspecific to D. mujtabai .

Baqri and Jairajpuri (1969) described a new species, D. arcuicaudatus , from Uttar Pradesh, India. Jana and Baqri (1981) redescribed this species based on two female specimens from West Bengal, India . Some doubts exist about the correct identity of the West Bengal population as it shows some major morphometric differences including a shorter and robust body (L = 0.68–0.75 vs 1.2–1.4 mm, a = 25–27 vs 31–36), shorter odontophore (12–14 vs 15–16 µm), lower b (4.7–5.2 vs 7.1–8.4) and c (18–20 vs 27–29) ratios and shorter prerectum (49–55 vs 110–117 µm) . Peralta and Peña-Santiago (1997) also commented on the Jana and Baqri (1981) population and did not consider the West Bengal population conspecific with D . arcuicaudatus. The morphometrics of this population is quite comparable to that of D. mujtabai Baqri (1991) . Taking into account this evidence, D. arcuicaudatus apud Jana and Baqri, 1981 is considered identical to D. mujtabai .

The present population also conforms well with the West Bengal population described by Jana and Baqri 1981 except in having a slightly longer prerectum (62–84 vs 49–55).

Figures

Figure 7. Dorylaimoides mujtabai Baqri, 1991 (LM photographs). (a, b) Anterior region; (c) anterior region showing amphid; (d) pharyngeal region; (e) expanded part of pharynx; (f) vulval region; (g,h) female genital system; (i) female posterior region. (j) male posterior region; (k) male posterior end. Scale bars: a–c, e–k = 10 μm; d = 20 μm.