Trefusialaimus idrisi, Leduc, 2013

Leduc, Daniel, 2013, Two new free-living nematode species (Trefusiina: Trefusiidae) from the Chatham Rise crest, Southwest Pacific Ocean, European Journal of Taxonomy 55, pp. 1-13 : 8-12

Trefusialaimus idrisi sp. nov.

Figs 3-4 ; Table 1

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Diagnosis and relationships

Trefusialaimus idrisi sp. nov. is characterised by relatively short body length, presence of numerous golden inclusions in the chords, cephalic setae 0.65-0.80 cbd long, spicules 2.3 abd long, 4 pairs of pericloacal papillae, and long, gradually tapering tail.

Until now, only two Trefusialaimus had been described, viz., T. magnus (Filipjev, 1946) and T. monorchis Riemann, 1974 . Trefusialaimus idrisi sp. nov. is similar to T. magnus in the shape of the copulatory apparatus and tail, but can be differentiated from the latter by the shorter body length (4540 vs. 7700 M m), lower value of c (7 vs. 21), longer cephalic setae (0.65-0.80 vs. 0.4 cbd), longer spicules (2.3 vs. 1.7 abd), and longer tail (38 vs. 11 abd). T. idrisi sp. nov. can easily be differentiated from T. monorchis by the markedly longer cephalic setae (0.65-0.80 vs. 0.26 cbd), absence of pre- and post-cloacal papillae (present in T. monorchis ), and tail shape (gradually tapering vs. conico-cylindrical).

Etymology

The species is named after Idris Matai Kljucanin Brun, the author’s godson.

Material examined

Holotype

♂, collected on 20 Feb. 2011 (NIWA cruise TAN1103, station 69), central Chatham Rise (43.331° S, 178.288° E), water depth 350 m, sediment depth 1-5 cm, mean grain size 55-59 µm, %sand 55-57%, particle sorting (geometric) 4.1-4.3 ( NIWA 88349 ).

Paratype

1 juvenile, same data as holotype ( NIWA 88350).

Description

Male

Body cylindrical, slender, tapering slightly towards anterior extremity ( Fig. 4D ), with slight golden colouration due to the presence of numerous round, ca. 1 µm diameter, golden inclusions in the chords (i.e., longitudinal thickenings of the hypodermis protruding internally between the sectors of the longitudinal muscles; Chitwood & Chitwood 1974) ( Fig. 4E ). Cuticle smooth, thin, ca. 0.7-0.9 µm thick, except in head region (anterior to cephalic setae) where it is slightly thicker, 1.0- 1.6 µm. Head rounded, slightly set-off from body due to thickened cuticle, with three lips, each bearing two small, conical inner labial papillae 1.0- 1.5 µm long ( Fig. 3B ). Six outer labial setae and four cephalic setae in one circle, double-jointed; cephalic setae slightly longer than outer labial setae (0.75-0.80 cbd vs. 0.65 cbd). Sub-cephalic and somatic setae absent. Amphid pocket-shaped with oval aperture, ca. 6 µm wide by 2 µm high ( Fig. 3A ). Buccal cavity funnel-shaped, without teeth. Pharynx cylindrical, slightly swollen at posterior extremity, completely surrounds buccal cavity. Pharyngeal lumen lightly but distinctly cuticularised at anterior extremity ( Figs 3B , 4B ). Nerve ring situated at ca. 50% of pharynx length. Secretory-excretory system not observed. Cardia small.

Reproductive system monorchic with single outstretched testis, ca. 1960 µm long. Position of testis relative to intestine difficult to ascertain. Elongated sperm cells, ca 3-5 µm wide by 13-16 µm long, with central rod and nucleus at one extremity ( Fig. 3G ); vas deferens ca. 520 µm long, without muscular ejaculatory duct. Paired, equal spicules, 2.3 abd long, slightly bent near distal one third, with broad proximal end and narrow pointed distal end; velum present ( Fig. 3D ). Gubernaculum with two pairs of narrow, pointed lateral crurae ( Fig. 3E ). Four pairs of small, conical peri-cloacal papillae ( Fig. 3F ). Precloacal supplements absent. Tail long, ca. 14% of total body length, narrow, gradually tapering, without setae ( Fig. 3H ).

Juvenile

Similar to male, but with shorter and narrower body, shorter cephalic setae ( Figs 3C , 4B ), and smaller amphid. Numerous sperm cells are present throughout the pseudocoelom from ca. 90 µm posterior to pharynx to ca. 200 µm anterior to anus ( Fig. 4C ). Genital and copulatory (i.e., cloacal or vulval) primordia not observed.

Discussion

The presence of sperm cells in the pseudocoelom of the juvenile Trefusialaimus idrisi sp. nov. specimen is unusual. Some nematode species, such as Oncholaimus oxyuris , can transfer sperm through traumatic insemination ( Coomans et al. 1988), a process whereby the male injects sperm directly into the body of a female (or potentially even a male or juvenile) by piercing the cuticle with the spicules. The presence of sperm cells in the juvenile specimen could be explained if a similar process occured in T. idrisi sp. nov. The existence of such a reproductive strategy, however, is highly conjectural because no Trefusialaimus females have ever been observed and (to my knowledge) traumatic insemination has not been described in the suborder Trefusiina .

Trefusialaimus idrisi sp. nov. was rare at the study site, with only four specimens (the two type specimens and two juveniles in poor condition, each from a different subcore) recorded out of the 4412 individuals that were identified by Leduc & Pilditch (2013). All individuals were found in the surface (0-1 cm) sediment layer (D. Leduc, unpublished data). A single juvenile specimen (out of 4550 specimens identified from 30 locations on the New Zealand continental margin) was recorded from a site on the northern flank of Chatham Rise at a depth of 1000 m (178.500° E, 44.333° S; silt/clay content 95%) ( Leduc et al. 2012a; D. Leduc unpublished data).

Figures

Fig. 3. Trefusialaimus idrisi sp. nov. A. Anterior body region of male. B. Head of male. C. Head of juvenile. D. Right spicule. E. Gubernaculum. F. Male copulatory apparatus. G. Mature sperm. H. Posterior body region of male. Scale bar: A = 40 µm; B-C, G = 20 µm; D-E = 14 µm; F = 28 µm; H = 75 µm.

Fig. 4. Trefusialaimus idrisi sp. nov. Light micrographs. A. Anterior body region of male, lateral view. B. Anterior body region of juvenile, dorsal view. C. Mid-body region of juvenile, showing sperm cells in pseudocoelom. D. Entire male. E. Lateral chord of male, showing round golden inclusions. Arrows point to sperm cells. Scale bar: A-C, E = 15 µm; D = 260 µm.