Lawtonema indicum, Islam & Ahmad, 2024

Islam, Md Niraul & Ahmad, Wasim, 2024, Oostenbrinkellus gen. n. and a new species of the rare nematode genus Lawtonema Siddiqi, 1998 (Nematoda: Dorylaimida: Tylencholaimoidea) from the Western Ghats, Zootaxa 5428 (1), pp. 75-90 : 85-89

Lawtonema indicum sp. n.

( Figs. 4 & 5 )

Materials examined. Three females and one male in good state of preservation.

Description. For measurements, see Table 2 .

Female: Slender medium sized nematodes, straight to slightly curved ventrad upon fixation; tapering gradually towards the anterior end and posteriorly narrowing to form a long filiform tail. Cuticle with two distinct layers, 1.0 µm thick anteriorly, 1.5–2.0 µm at midbody and 2.0–2.5 μm on the tail. Outer cuticle thin, smooth; inner layer thicker than outer, slightly loose, striated, radial refractive elements indistinct. Lateral chords occupying about one-third of the midbody diameter. Lateral, dorsal and ventral body pores indistinct. Lip region cap-like, continuous with the body or offset by slight depression, 1.9–2.2 times as wide as high or about one-fourth of body diameter at the pharyngeal base. Lips rounded, amalgamated, inner part elevated forming a prominent labial disc. Amphidial fovea large cup-shaped, their aperture occupying about three-fourths of the lip region diameter. Odontostyle asymmetrical, long, slender, tip beak-like, bent slight dorsally, 1.4–1.6 times the lip region diameter long, its aperture about one-sixth of the odontostyle length. Odontophore simple, rod-like with slightly basal thickening, as long as the odontostyle length. Guiding ring strongly sclerotized, refractive, at 1.1–1.2 times lip region diameter from the anterior end. Pharynx consists of slender and weakly muscular anterior part, expanding gradually into a short cylindrical bulb; occupying about 19–20% of total pharyngeal length. Pharyngeal gland nuclei often visible. Nerve ring at 47–51% of the pharyngeal length from the anterior end. Cardia long, elongate-cylindroid, one-half to three-fifths of the corresponding body diameter long. Genital system didelphic-amphidelphic. Ovaries reflexed, length 47–53 µm (anterior) and 56–96 µm (posterior); oocytes arranged in a single row except near tip. Oviduct joining the ovary sub-terminally, measuring 45–48 µm (anterior) and 51–78 µm (posterior), consisting of a slender distal portion and well-developed pars dilatata. Oviduct-uterus junction marked by well-developed sphincter. Uterus short with wide lumen, length 38–47 µm (anterior) and 41–53 µm (posterior). Sperm cell present throughout the uterus and oviduct. Vagina cylindrical, extending inwards, 13.5–14.0 µm or about one-half (48–50%) of midbody diameter; pars proximalis vaginae 9.5–10.5 × 4.5–6.0 µm, its wall encircled by circular muscles; pars distalis vaginae 3.0–3.5 µm with slightly curved walls; pars refringens absent. Vulva a transverse slit. Prerectum 3.3-3.5 and rectum 1.5–1.7 times anal body diameter long. Tail long filiform, tapering gradually, 12.7–13.2 times anal body diameter long with a pair of distinct caudal pores on each side.

Male: General morphology similar to female except for the posterior region being more ventrally curved. Genital system diorchic, testes opposed, sperm cell spindle-shaped. Supplement an adcloacal pair, situated at 6.0 µm from the cloacal aperture, a single ventromedian supplements located outside the range of spicules, 36 μm from the adcloacal pair. Spicules typical dorylaimoid, curved ventrad, slender, 7.0 times as long as wide and 1.6 times as long as cloacal body diameter, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 140º, head occupying 18% of total spicules length, median pieces 16 times as long as wide, occupying 37% of the spicules maximum width, reaching the spicules tip, posterior end 2 μm wide. Lateral guiding pieces distinct, rod-like, about six times as long as wide or about one-fourth of the spicules length. Prerectum 3.2 and rectum 1.8 cloacal body diameter long respectively. Tail long filiform, tapering gradually, 10.5 times cloacal body diameter long, with a pair of caudal pores on each side.

Type habitat and locality. Soil samples from around the roots of shrubs (unidentified) from Balli , South Goa district, Goa State, India; coordinates 15º08’49.9’’N 74º01’14.5’’E; 10 April, 2016, collected by Md Niraul Islam.

Type specimens. Holotype female on slide Lawtonema indicum sp. n. /1; paratype females and male on slides Lawtonema indicum sp. n. / 2–3; deposited in the nematode collection of the Department of Zoology, Aligarh Muslim University (AMU/ZD/NC), as well as with nematode collection of the Zoological Survey of India, Kolkata, India.

Etymology. The new species is named Lawtonema indicum sp. n. because of its type locality India.

Diagnosis and relationships. Lawtonema indicum sp. n. is characterized by having a 0.94–1.28 mm long body; lip region cap-like, continuous with the body or offset by slight depression; lips rounded, amalgamated, inner part elevated forming a labial disc; odontostyle slender, 10.0–10.5 μm long with its tip dorsally bent, odontophore 9.5–10.0 μm long, total stylet length 19.5–20.0 μm; pharynx slender with slightly muscular anterior part, expanding gradually into a short cylindrical bulb, occupying about 19–20% of the total neck length; female genital system amphidelphic; tail long filiform; similar in sexes; 12.7–13.2 times anal body diameter long; male with 29 μm long spicules, lateral guiding pieces and a single ventromedian supplement located outside the range of spicules.

The new species differs from the type and only known species of the genus, L. lawtoni Siddiqi, 1998 , in having a shorter body (Female, L=1.25–1.28 vs 1.59 mm, Male 0.94 vs 1.4–1.6 mm); differently shaped amphidial fovea (cup-shaped vs stirrup-shaped), longer odontostyle (10.0–10.5 vs 7.0 µm), shorter odontophore (9.5–10.0 vs 14 µm); shorter pharyngeal bulb (35–39 vs 50 µm or 19–20 vs 22% of total neck length); vulva transverse (vs vulva pore-like); shorter prerectum (3.3–3.5 vs 7.0 times anal body diameter long); shorter tail (211–220 vs 240 µm or ć=12.7–13.2 vs 15) and fewer ventromedian supplements (1 vs 2).

Note. After Camera Lucida the male specimen was crushed accidentally during photography.

Figures

FIGURE 4. Lawtonema indicum sp. n. A. Entire Female; B.Anterior region C.Anterior region showing amphid; D. Pharyngeal bulb; E. Pharyngeal region; F. Female genital system; G. Vulval region; H. Female posterior region; I. Male posterior region.

FIGURE 5. Lawtonema indicum sp. n. A & B. Anterior region; C. Anterior region showing amphid; D. Pharyngeal region; E & F. Pharyngeal bulb; G. Female genital system; H. Vulval region; I. Spicules; J. Female posterior region showing prerectum; I. Female posterior end. (Scale bars: A–C, E, F & H–J =10 µm, D, G & K= 20 µm)