Oostenbrinkellus ventrostylus ( Dhanam and Jairajpuri, 1999 ) 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 : 77-85

Oostenbrinkellus ventrostylus ( Dhanam and Jairajpuri, 1999) comb. n.

= Oostenbrinkella ventrostylus Dhanam and Jairajpuri, 1999

( Figs. 1–3 )

Materials examined. Forty females and twenty-nine males in good state of preservation.

Description. For measurements, See Table 1 .

Female: Slender medium sized nematodes, 0.92–1.3 mm long, 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 in the anterior region, 1.5–2.0 µm at midbody and 2.0–2.5 μm on tail. Outer cuticle thin, with fine transverse striations; inner layer thicker than outer, slightly loose, finely striated. Lateral chords occupying about 24–32% of the midbody diameter. Lateral, dorsal and ventral body pores indistinct. Lip region cap-like, almost continuous or offset by slight depression, 1.5–2.0 times as wide as high or about one-fourth to one-third of the body diameter at the pharyngeal base. Lips rounded, amalgamated; inner part elevated forming a labial disc. Amphidial fovea large cup-shaped, their aperture occupying about two-thirds to four-fifths of the lip region diameter. Odontostyle long, slender, slightly sigmoid, tip beak-like, bent slight dorsally, mid part slight curved dorsally, 1.6–2.0 times the lip region diameter long, with a ventral accessory piece covering the posterior half of the ventral side; its aperture one-seventh to one-sixth of the odontostyle length. Odontophore simple, rod-like with basal knobs, 0.6–0.8 times the odontostyle length. Guiding ring strongly sclerotized, refractive, at 1.0–1.4 times lip region diameter from the anterior end. Pharynx Consisting of a slender and weakly muscular anterior part, expanding gradually into a short cylindrical bulb, occupying 19–25% of total the pharyngeal length. Pharyngeal gland nuclei often visible. Nerve ring at 45–51% of the pharyngeal length. Cardia long, elongate-cylindroid, one-third to one-half of the corresponding body diameter long. Genital system monodelphic-opisthodelphic. Ovary reflexed, measuring 39–141 µm long; oocytes arranged in a single row except near tip. Oviduct joining the ovary sub-terminally, measuring 45–113 µm long and consisting of a slender portion and well-developed par dilatata. Oviduct-uterus junction marked by more or less developed sphincter. Uterus long, tubular, bipartite, consists of a wider proximal part followed by narrower distal part, filled with sperm, measuring 29–56 µm. Anterior genital branch reduced to a simple sac, 16–40 µm or 0.7–1.6 times the midbody diameter long. Sperm cell present throughout the uterus and oviduct. Vagina cylindrical, extending inwards, 10.5–14.0 µm or two-fifths to three-fifths (42–59%) of midbody diameter; pars proximalis vaginae 6.5–9.0 × 4.0–6.0 µm long, its wall encircled by circular muscles; pars distalis vaginae 2.5–3.5 µm with slightly curved walls; pars refringens absent. Vulva a minute pore ( Fig. 3 B ). Prerectum 2.0–4.4 and rectum 1.1–1.8 times anal body diameter long. Tail long filiform, tapering gradually, 11.1–17.3 times anal body diameter long with a pair of distinct caudal pores on each side.

Male: General morphology similar to that of female except for the posterior region being slight ventrally curved. Genital system diorchic, testes opposed, sperm cell spindle-shaped, 4.0–5.0 μm long. Supplements an adcloacal pair, situated at 6.0–8.0 µm from the cloacal aperture, rarely also a single ventromedian supplement located outside the range of spicules; 33–52 μm from the adcloacal pair. Spicules typical dorylaimoid, curved ventrad, slender, 5.7–7.4 times as long as wide and 1.4–1.8 times as long as body diameter at the level of cloacal aperture, dorsal contour regularly convex, ventral contour bearing a moderately developed hump and hollow, curvature 140–145º, head occupying 17–20% of the total spicules length, median pieces about 15–16 times as long as wide, occupying 37% of the spicules maximum width, reaching the spicules posterior tip, posterior end 1.0–1.5 μm wide. Lateral guiding pieces distinct, rod-like, about 6.0–8.0 times as long as wide or about one-fourth to one-third of the spicules length. Prerectum 2.7–4.4 and rectum 1.4–2.4 times cloacal body diameter long. Tail long filiform, tapering gradually, 10.0–15.7 times cloacal body diameter long, with a pair of caudal pores on each side.

Habitats and localities. Soil samples collected from around the roots of,

i). grasses (unidentified) from Yaraganalu , Shivamoga district, Karnataka State, India; coordinates 13º48’04.3’’N 75º34’23.4’’E.

ii). grasses (unidentified) from Kalady , Ernakulum district, Kerala State, India; coordinates 11º03’40.7’’N 76º327’23.8.’’E.

iii). grasses (unidentified) from Mundur , Palakkad district, Kerala State, India; coordinates 10º52’14.6’’N 76º33’08.6’’E.

iv). Arecanut ( Areca catechu ) from Vazhayoor, Kozhikode district, Kerala State, India; coordinates 11º13’14.8’’N 75º54’07.0’’E.

v). grasses (unidentified) from Chungathara forest , Malappuram district, Kerala State, India; coordinates 11º20’01.1’’N 76º16’32.44’’E.

vi). shrubs (unidentified) from Balli , South Goa district, Goa State, India; coordinates 15º08’49.9’’N 74º01’14.5’’E.

vii). grasses (unidentified) from Thattekadu , Ernakulam district, Kerala State, India; coordinates 10º07’33.6’’N 76º41’02.4’’E.

Remarks. Although the present populations were collected from several localities, the morphometrics of all seven populations distinctly overlap and are quite similar. The only distinct difference observed was in the male specimens of the Malappuram population which possessed a single ventromedian supplement ( Fig. 3 G ), compared to males of all other populations which did not have any ventromedian supplements. Since there is no other morphological or morphometric difference, this population is considered conspecific. The morphometrics of the newly collected populations also conform well with the type population except in having slight variation in the structure of amphidial fovea. In the present study a large number of specimenswere studied and they all have simple cup-shaped amphidial fovea, whereas; in the original description the amphids were described as duplex. This may be a misinterpretation or an error in the original description.

Figures

FIGURE 1. Oostenbrinkellus ventrostylus (Dhanam and Jairajpuri, 1999) comb. n. A. Entire female; B. Entire male; C–E. Anterior region; F. Anterior region showing amphid; G. Pharyngeal bulb; H. Pharyngeal region; I. Female genital system; J & K. Male posterior region; L. Female posterior region.

FIGURE 2. Oostenbrinkellus ventrostylus (Dhanam and Jairajpuri, 1999) comb. n. A–E. Anterior region, arrow showing ventral stiffening piece; F. Anterior region showing amphid; G–I. Pharyngeal bulb. (Scale bars: A–I=10 µm)

FIGURE 3. Oostenbrinkellus ventrostylus (Dhanam and Jairajpuri, 1999) comb. n. A & B. Vulval region; C–E. Female genital system (arrow showing the sphincter); F–I. Male posterior region showing spicules, arrow showing ventromedian supplement; J. Male posterior end; K. Female posterior region. (Scale bars: A–D & F–G =10 µm; E, J & K= 20 µm)