Pseudonchus virginiae, Leduc, Daniel & Verschelde, Dominick, 2013

Leduc, Daniel & Verschelde, Dominick, 2013, One new genus and two new free-living nematode species (Desmodorida, Desmodoridae) from the continental margin of New Zealand, Southwest Pacific Ocean, Zootaxa 3609 (3), pp. 274-290 : 284

Genus Pseudonchus Cobb, 1920

Pseudonchus virginiae sp. n. ( Figs 5–6 , Table 1 )

Type sepcimens. Holotype male, collected 6 April 2007 (NIWA cruise TAN0705, station 45), southwestern Chatham Rise (44.485° S, 177.141° E), water depth: 1240 m, sediment depth: 1–5 cm, silt/clay content: 82.9%, CaCO3 content: 38.5%, sediment chlorophyll a concentration: 32 ng /gDW sediment (NIC 865971). Paratype female, same data as holotype (NIC 865972).

Etymology. The species is named in honour of Virginie Gagnon-Leduc.

Description. Male. Stout cylindrical body, orange colour, tapering slightly towards head and tail. Cuticle thin (1–2 Μm thick), with slight transverse striations beginning posterior to cephalic setae to tail tip. No lateral differentiation. Eight rows of short (2 Μm), sparse somatic setae, each connected to a single, nucleated gland, mostly visible in anterior region. Chords with numerous, irregularly-shaped, dark orange inclusions ( Figure 7 D).

Six setiform outer labial sensillae and four slightly longer cephalic setae. Inner labial sensillae not observed. Sub-cephalic setae absent. Cryptocircular amphideal fovea turning ventrally and smaller, circular amphideal aperture. Large buccal cavity divided into anterior protostomal and posterior metastomal regions, heavily cuticularised. Anterior margin of protostome with two rows of seven incurving teeth. Six larger teeth at junction of protostome and mesostome, two dorsally and four ventrosublaterally. Pharynx muscular, surrounding metostome, with small terminal bulb. One ventral and two dorsosublateral pharyngeal tubes. Nerve ring at 60% of pharynx length from anterior. Secretor-excretory system not observed. Cardia short.

Reproductive system monorchic with one anterior, outstretched testis situated ventrally relative to intestine. Short, arcuate spicules with well-developed capitulum. Short, slightly bent gubernaculum. Five short pre-cloacal setae, beginning 32 Μm anterior of cloaca, 27–33 Μm apart. Short conical tail, with three caudal glands and welldefined spinneret.

Female. Similar to male, but with greater body diameter and smaller, multispiral (1.3–1.4 turns) amphids. Reproductive system with two reflexed ovaries situated ventrally relative to intestine. Vulva located at almost two thirds of body length.

Diagnosis and relationships. Pseudonchus virginiae sp. n. is characterised by short cephalic setae, sexual dimorphism in amphid shape (cyptocircular amphideal fovea in males vs multispiral in females), short arcuate spicules with capitulum, five regularly-spaced precloacal setae, and short conical tail.

Nine valid Pseudonchus species have been described so far, viz., P. rotundicephalus Cobb, 1920 , P. symmetricus De Coninck, 1942 , P. kosswigi Murphy, 1964 a, P. j e n s e n i Murphy, 1964b, P. gerlachi (Gerlach, 1953) Warwick, 1969 , P. deconincki Warwick, 1969 , P. northumbriensis Warwick, 1969 , P. decempapillatus Ward, 1974 , and P. pachysetosus Blome, 1982 . P. virginiae n. sp. can be distinguished from all other species of the genus based on the combination of the following characters: relatively small body size (1100–1200 Μm), short tail (<2.0 abd), and presence of five small precloacal setae.

Discussion. This is the first record of the genus Pseudonchus within the New Zealand region, and, to our knowledge, from the deep sea (> 200 m water depth). This genus is unusual in that the dorsal sector of the buccal cavity has been lost, resulting in a lateral symmetry instead of the usual triradial symmetry found in most other nematode taxa. This loss of the dorsal sector is mostly restricted to the labial and buccal regions, however, and only affects the anterior extremity of the pharynx, as suggested by De Coninck (1945) based on observations on P. symmetricus . The presence of three marginal tubes in the pharynx of P. virginiae sp. n. (one ventral and two dorsosublateral) is consistent with these observations.

Figures

FIGURE 5. Pseudonchus virginiae sp. n. A: Entire male in cross-section view; B: lateral view of male posterior region; C: female reproductive system. Scale bar: A = 150 Μm; B and C = 53 Μm.

FIGURE 6. Pseudonchus virginiae sp. n. A: Lateral view of male anterior region; B: lateral view of male head showing buccal cavity; C: lateral view of female head; D: female tail. Scale bar = 30 Μm.

FIGURE 7. Pseudonchus virginiae sp. n. Light micrographs. A: Lateral view of female head showing anterior portion of buccal cavity and teeth (optical section); B: lateral surface view of female head, showing multispiral amphideal fovea and cuticle striations; C: lateral surface view of male head showing cryptocircular amphideal fovea; D: lateral view of male middle body region showing lateral chord with granular inclusions. Scale bar: A, B and C = 20 Μm; D = 27 Μm.