Cobbionema trigamma, Leduc, 2013

Leduc, Daniel, 2013, Two new genera and five new species of Selachinematidae (Nematoda, Chromadorida) from the continental slope of New Zealand, European Journal of Taxonomy 63, pp. 1-32 : 15-19

Cobbionema trigamma sp. nov.

Figs. 8-10 , Table 2

urn:lsid:zoobank.org:act:06CDA8B6-C525-46E9-9D04-05C4923651D8

Diagnosis

Cobbionema trigamma sp. nov. is characterised by four long cephalic setae and six smaller outer labial setae in one circle, amphideal fovea with 4.25 turns, six rhabdions surrounding anterior buccal cavity, each with two pairs of pointed projections at their posterior extremities, posterior buccal cavity widening posteriorly and with three pairs of rhabdions fused posteriorly and widening anteriorly, males with two testes pointing anteriorly and with reflexed posterior testis, spicules 2.5 abd long, and no pre-cloacal supplements.

Etymology

The species name is derived from the Greek letter γ (gamma), and refers to the presence of three pairs of rhabdions fused posteriorly (i.e., gamma-shaped) in the posterior buccal cavity.

Material examined

Holotype

NEW ZEALAND: ♂, NIWA 88359 , 6 Apr. 2007, NIWA cruise TAN0705, station 45, southern flank of Chatham Rise, 44.4864° S, 177.1407° E, 1238 m, silt/clay (93.9%).

Paratypes

NEW ZEALAND: 1 ♂, NIWA 88360, 8 Oct. 2001, TAN0116, station U2593A, southern flank of Chatham Rise, 44.3333° S, 178.5000° E, 1200 m, silt/clay (63.8%), fine sand (16.0%), very fine sand (13.6%). 1 ♀, NIWA 88361, 26 Apr. 2007, NIWA cruise TAN0705, station 271, northern flank of Chatham Rise, 42.6216° S, 175.9262° E, 1210 m, fine sand (60.3%), medium sand (29.3%).

Description

Males

Body cylindrical, tapering slightly towards both extremities. Cuticle 1.5-3.0 μm thick, thickest in tail region, with transverse rows of punctations, without lateral differentiation except in mid-body region, where punctations are irregularly spaced and further apart; lateral rows of oval-shaped cuticle pores, 1.5- 2 × 2-3 μm, beginning from halfway down pharynx to anterior portion of tail ( Fig. 10B ). Somatic setae short and sparse, irregularly distributed. Head blunt, not set off, with six lips surrounding mouth opening. Inner labial papillae minute; six small outer labial setae situated slightly anterior to four conspicuously longer cephalic setae, 0.3-0.5 cbd. Amphideal fovea multispiral with 4.25 turns, with circular outline. Buccal cavity voluminous, divided into anterior and posterior portion. Anterior portion of buccal cavity cylindrical, with six cuticularised rhabdions, each with two pairs of large, pointed projections at posterior extremity ( Fig. 10A ). Posterior buccal cavity cone-shaped, widest at posterior extremity, with three pairs of rhabdions fused posteriorly and gradually widening anteriorly ( Fig. 10A ). Pharynx with conspicuous anterior bulb surrounding posterior portion of buccal cavity and part of anterior buccal cavity; pharynx widens posteriorly but not forming true posterior bulb. Nerve ring at 45% of pharynx length from anterior. Secretory-excretory (S-E) system present, cellular body of ventral gland situated immediately posterior to pharynx, pore situated 0.1-0.5 cbd posterior to nerve ring. Intestine cells with numerous round inclusions, most dense in cells immediately posterior to pharynx ( Fig. 8D ).

Reproductive system with two testes pointing anteriorly, with outstretched anterior testis and reflected posterior testis. Anterior testis on left of intestine, posterior testis on right of intestine. Large globular sperm cells, 6-9 × 10-13 μm. Spicules paired, 2.5 abd long, curved, swollen at proximal end and at ~ 55% of spicule length from proximal portion, then tapering distally. Gubernaculum bent, with lateral pieces (crurae) flanking distal ends of spicules. Pre-cloacal supplements absent; one small pre-cloacal seta. Tail conico-cylindrical with short, sparse setae and pointed extremity. Three caudal glands and spinneret present.

Female

Similar to male. Reproductive system didelphic-amphidelphic with reflected ovaries. Anterior ovary on left of intestine, posterior ovary on right of intestine. Vulva located at ~ 40% of body length from anterior

extremity. Pars proximalis vaginae surrounded by constrictor muscle, vaginal glands not observed. Anus not observed.

Remarks

Cobbionema trigamma sp. nov. is similar to C. acrocerca but differs from the latter in having a posterior buccal cavity with three pairs of rhabdions fused posteriorly and widening anteriorly, whereas C. acrocerca possesses a posterior buccal cavity with three irregularly-spaced rhabdions narrowing posteriorly and bearing hooks at their anterior extremities. C. trigamma sp. nov. differs from C. capense in the absence of denticles in the buccal cavity, and in the number (24 in C.trigamma sp. nov. vs. 7 in C. capense ) and orientation of pointed projections (all pointing posteriorly vs. some pointing anteriorly in C. capense ; pointed projections referred to as “teeth” in Furstenberg & Heyns 1987).

There was a substantial (> 2-fold) difference in size between the holotype and the paratype male. The two males also differed in the size of the amphid (0.28 vs. 0.52 cbd) and tail length (2.2. vs. 2.8 abd), but were identical in the size and arrangement of head sensillae, buccal cavity structure, and copulatory apparatus.

The buccal cavity of Cobbionema trigamma sp. nov. closely resembles that of Halichoanolaimus . H. robustus (Bastian, 1865) , H. consimilis Allgén, 1933 , H. quattuordecimpapillatus Chitwood, 1951 and H. dolichurus Ssaweljev, 1912 , for example, all have an anterior buccal cavity surrounded by rhabdions with pointed projections or hooks (the latter often in pairs) and a posterior buccal cavity surrounded by three pairs of rhabdions fused posteriorly (see figs 6-9 in Gerlach 1964).

The female of Cobbionema trigamma sp. nov. appears to lack an anus, a feature that has also been observed in several Halichoanolaimus species ( Gourbault & Vincx 1985). The absence of an anus was also noted by Schuurmans-Stekhoven (1950) in C. cylindrolaimoides (“the anal cleft could not be located”). The latter author cast doubt on the observations of Filipjev (1922), who drew the anus of C. acrocerca very far posteriorly near the cylindrical portion of the tail, which could suggest that the anus is in fact absent in C. acrocerca as well.

Cobbionema trigamma sp. nov. is unusual among the Selachinematidae in the structure of the testes (two testes anteriorly with posterior testis reflexed), and Choniolaiminae in lacking pre-cloacal supplements. Because this is the first time that male Cobbionema specimens are described, it remains unclear whether these are characteristic of other species of the genus.

Figures

Fig. 8. Cobbionema trigamma sp. nov. A. Surface view of holotype head. B. Surface view of paratype male head. C. Buccal cavity of paratype male. D. Holotype anterior body region. E. Spicule and gubernaculum of holotype. F. Holotype posterior body region. G. Paratype male posterior body region. H. Female posterior body region. Scale bar: A-C = 30 μm; D = 80 μm; E = 36 μm; F-G = 70 μm; H = 40 μm.

Fig. 9. Cobbionema trigamma sp. nov. A. Entire holotype. B. Entire female. C. Entire male paratype. Scale bar = 100 μm.

Fig. 10. Cobbionema trigamma sp. nov. Light micrographs. A. Buccal cavity of holotype. B. Cuticle of holotype, showing cuticle pores. Scale bar: A = 25 μm; B = 12 μm.