Halichoanolaimus ovalis Ditlevsen 1921

Halichoanolaimus ovalis Ditlevsen, 1921

Table 1, Figs 1–3

NEW ZEALAND • 2 ♂♂, 1 ♀; Kaikōura Canyon, 42.5082° S, 173.6325° E; water depth 1061 m; voyage TAN1006 station 7, site K4; 3 May 2010; NIWA 139245.

North Arm of Carnley Harbour, Auckland Islands.

Males

BODY. Cylindrical, tapering slightly towards anterior extremity. Cuticle with transverse rows of punctations; lateral differentiation consisting of larger, more widely spaced punctations. Two dorsosublateral rows of

pore complexes extending from posterior to nerve ring to cloacal region, each pore complex ca 1.5 µm in diameter, becoming more closely spaced posteriorly. Up to two or three ventrosublateral pore complexes also present in pharyngeal region or slightly posterior to pharynx. Eight longitudinal rows of short, sparse somatic setae, 2–3 µm long. Cephalic region slightly rounded, with slight indentation immediately posterior to cephalic setae. Lip region not conspicuously differentiated, bearing six inner labial papillae. Six short outer labial papillae, 2 µm long, located at base of labial region and at same level as four cephalic papillae of same length. Amphideal fovea multispiral with 5.0 to 5.25 turns, situated ~0.4 cbd from anterior end. Buccal cavity (pharyngostome) large, 25–30 µm deep, divided into anterior (gymnostome) and posterior portions (stegostome). Anterior portion of buccal cavity cup-shaped, with three sets of six cuticularized rhabdions, 12–14 µm long, terminating in three sets of at least six pairs (one anterior and one posterior) of denticles; posterior portion of buccal cavity narrower, cylindrical, surrounded by three Y-shaped pairs of cuticularized rhabdions with swollen bases, 15–17 µm long. Pharynx cylindrical, muscular, without anterior or posterior bulb. Nerve ring at ca 45–50% of pharynx length from anterior. Secretory-excretory system present; renette cell up to 18 µm wide and 18 µm long, situated at level of cardia. Several nucleated pseudocoelomocytes also present around base of pharynx and either side of secretory-excretory duct; ampulla slightly smaller than renette cell, pore situated posterior to nerve ring. Cardia small, surrounded by intestine; posterior extremity of intestine blind.

REPRODUCTIVE SYSTEM. Diorchic with outstretched testes. Anterior testis to the right or ventrally to intestine, posterior testis to the left side of intestine. Sperm cells globular, 8–12 × 15–17 µm. Spicules paired, curved, tapering distally, length 1.5–1.6 body diameters at level of cloacal opening; minute ventral denticle present at one third of spicule length from distal tip, interior of spicules granular in appearance. Gubernaculum consisting of two detached lateral pieces (crurae) tapering distally, median portion of gubernaculum (corpus and cuneus) not visible. Seven precloacal supplements present, consisting of conical papillae set on cylindrical cuticular elevations each with internal duct, supplements located 10– 14 µm from each other. Tail conicocylindrical with cylindrical portion ca two thirds of total tail length; a few short and sparse somatic setae present subventrally and subdorsally. Three caudal glands located posterior to spicules, spinneret present.

Females

Similar to males but with slightly longer tail. Reproductive system didelphic-amphidelphic, with reflexed ovaries. Anterior ovary to the left of intestine and posterior ovary to the right of intestine. Vulva situated at mid-body. Mature eggs not observed. Proximal portion of vagina surrounded by constrictor muscle, two large and conspicuous vaginal glands with coarsely granulated cytoplasm and large nucleus present. Intestine blind, no rectum or anus.

Halichoanolaimus ovalis was originally described by Ditlevsen (1921) based on two females from the Auckland Islands, and males were later described from the littoral zone of Campbell Island by Allgén (1927) (both Auckland and Campbell islands are located in the Southern Ocean directly south of New Zealand’s South Island). The female specimen from Kaikōura Canyon broadly resembles the original description of Ditlevsen (1921), although the Kaikōura Canyon female is shorter (body length 1.4 vs 1.8 mm in H. ovalis) and has a higher ratio of ‘a’ (24 vs 18). Ditlevsen (1921) states that the amphideal fovea of H. ovalis females has six turns; however, his figure shows only five turns, which is consistent with the Kaikōura Canyon specimen. The present description is also consistent with the observation of conspicuous vaginal glands with coarsely granulated cytoplasm by Ditlevsen (1921). The two male specimens from Kaikōura Canyon agree well with the description of Allgén (1927) in general body dimensions, although like the Auckland Islands specimens, the Campbell Island specimens are somewhat stouter as indicated by a lower value of ‘a’ (17) relative to the Kaikōura Canyon specimens (22). In addition, Allgén counted only four amphideal fovea turns in his male specimens compared to five in the Kaikōura Canyon specimens. However, the structure of the copulatory apparatus, as well as the shape and number of precloacal supplements, are the same.

The intestine of one of the male H. ovalis specimens contained the anterior half of a nematode prey which was identified as belonging to Halalaimus de Man, 1888 based on the structure of the cuticle, amphideal fovea and buccal cavity. The intestine of the other H. ovalis male (from the same sample) contained the posterior half of a nematode, possibly also belonging to the genus Halalaimus.