Bolbolaimus tongaensis, Leduc, 2016

Leduc, Daniel, 2016, One new genus and three new species of deep-sea nematodes (Nematoda: Microlaimidae) from the Southwest Pacific Ocean and Ross Sea, Zootaxa 4079 (2), pp. 255-271 : 265

Bolbolaimus tongaensis n. sp.

( Figs. 3 & 4 ; Table 1)

Diagnosis. B. tongaensis n. sp. is characterised by annulated cuticle with faint longitudinal bars, two subventral rows of short somatic setae on main part of body, oval amphideal aperture and cryptocircular amphideal fovea situated between cephalic setae and only partially surrounded by cuticule annulations, cuticularised buccal cavity with dorsal tooth and to smaller subventral teeth, short and curved spicules cuticularised along dorsal edge and at proximal end but not along ventral edge, and with swollen portion near proximal end, short and simple gubernaculum without crurae, and precloacal supplements absent.

Etymology. The species name is derived from the type locality.

Material examined. Holotype male ( NIWA 99770 ), collected 15 October 2013 (JAMSTEC cruise YK13-10, Shinkai Dive 1370), edge of Tonga Trench, Southwest Pacific (174.2917º W, 23.6083º S); water depth: 6254 m . Paratype female ( NIWA 99771 ), same data as holotype .

Description. Male Body cylindrical, tapering slightly towards both extremities, with faint golden colouration. Cuticle annulated from immediately posterior to cephalic setae to near tail tip; faint longitudinal bars visible at level of nerve ring and posteriorly. Two ventrosublateral rows and two dorsosublateral rows of short somatic setae observed in pharyngeal region region; two subventral rows of somatic setae present between pharynx and cloaca. Porids and epidermal glands not observed. Head blunt, not set off from rest of body. Six inner labial papillae and six outer labial papillae in two separate circles; four short cephalic setae situated further posteriorly at mid-level of amphideal fovea, 0.13 corresponding body diameter (cbd) long. Cryptocircular amphideal fovea with cuticularised outline, situated 0.25 cbd from anterior and only partially surrounded by cuticule annulations; oval amphideal aperture, smaller than amphideal fovea, 4 × 5 µm ( Fig. 3A ). Buccal cavity medium-sized, funnel-shaped, cuticularised, with dorsal tooth and two smaller sub-ventral teeth. Cheilostoma with twelve longitudinal folds. Pharynx surrounding buccal cavity slightly swollen, forming a small bulb; muscular posterior pharyngeal bulb present, oval-shaped. Secretory-excretory system present; renette cell situated slightly posterior to cardia, 20 × 10 µm; excretory pore not observed. Nerve ring situated slightly posterior to middle of pharynx length from anterior. Cardia 9 µm long, not surrounded by intestinal tissue.

Reproductive system diorchic, testes opposed and outstretched. Sperm cells globular, maximum dimensions 6 × 7 µm. Two equal spicules, 1.25 cloacal body diameters long, cuticularised along dorsal edge and at proximal end, but not along ventral edge; swollen portion near proximal end. Gubernaculum short, simple, mostly straight, situated dorsally relative to spicules and without crurae. Precloacal supplements not observed. Tail conical, with three pairs of short and stout sub-ventral setae. Three caudal glands and spinneret present.

Female Similar to male in most respects, but with lower value of a, more conspicuous longitudinal bars visible along entire body, and fewer caudal setae. A fine groove visible at level of outer labial papillae, suggesting an extendable anterior cephalic region (as commonly seen in the Desmodorinae ). Reproductive system didelphic, with opposed and outstretched genital branches both situated ventrally relative to intestine. Vulva situated slightly posterior to mid-body, at right angle with body wall. Mature egg 22 × 42 µm. Proximal portion of vagina surrounded by constrictor muscle.

Differential diagnosis. Bolbolaimus tongaensis n. sp. is most similar to B. bahari in the position and size of head sensillae and amphideal fovea. The new species can be distinguished from B. bahari by the shape of the spicules and gubernaculum. The spicules of B. tongaensis n. sp. are only cuticularised along the dorsal edge and at proximal end only and have swollen portion near the proximal end, whereas the spicules of B. bahari are uniformly cuticularised and do not have a swollen portion. In addition, the gubernaculum of B. tongaensis n. sp. is short and straight whereas the gubernaculum of B. bahari is strongly curved proximally. Bolbolaimus tongaensis n. sp. also differs from B. bahari by the longer body (males: 476 vs 328–411 µm), shorter spicules (25 vs 34–35 µm) and shorter gubernaculum (8 vs 13–14 µm).

Figures

FIGURE 3. Bolbolaimus tongaensis n. sp. Holotype. A: Lateral surface view of head; B: anterior body region; C: entire male; D: posterior body region. Scale bar: A = 20 µm; B & D = 25 µm; C = 62 µm.

FIGURE 4. Bolbolaimus tongaensis n. sp. Female. A: Lateral view of head; B: anterior body region; C: entire female; D: posterior body region. Scale bar: A = 20 µm; B = 40 µm; C = 75 µm; D = 30 µm.