Stygodesmodora confusa, Leduc & Verschelde, 2015

Leduc, Daniel & Verschelde, Dominick, 2015, New Spirinia and Stygodesmodora species (Nematoda, Spiriniinae) from the Southwest Pacific, and a revision of the related genera Spirinia, Chromaspirina and Perspiria, European Journal of Taxonomy 118, pp. 1-25 : 15-20

Stygodesmodora confusa sp. nov.

urn:lsid:zoobank.org:act:44B8B268-21AE-4E30-8A7E-D707B1D54C8F

Figs 4–7 ; Table 1

Diagnosis

Stygodesmodora confusa sp. nov. is characterised by a relatively short body (778–1241 µm), spiral amphids with 1.0–1.25 turns, cephalic setae situated at or slightly posterior to mid-level of amphid, and males with four precloacal supplements consisting of short setae on wide bases.

Type specimens

Holotype

NEW ZEALAND: ♂, NIWA 88377 , 24 Apr. 2010, NIWA cruise TAN1004, station 92, canyon axis on southern Hikurangi Margin , 41.8921° S, 174.6347° E, 686 m.

Paratypes

NEW ZEALAND: 1 ♂, 2 ♀♀, NIWA 88378, 20 Feb. 2011, NIWA cruise TAN1103, station 69, central Chatham Rise, 43.331° S, 178.288° E, 350 m; 3 ♀♀ (same data as other paratypes) were measured to provide morphometric data and then processed for scanning electron microscopy.

Etymology

The species name is derived from the Latin adjective confusus, meaning confused, perplexed or obscure (feminine form used, as - dora is feminine), and refers to the close affinities of this species with other desmodorid genera (see Remarks), which resulted in initial confusion in the placement of this species.

Description

Male

Relatively short cylindrical body, pale golden colour, tapering slightly towards both ends. Cuticle 0.9– 1.4 µm thick, with coarse annuli, approximately 1 µm apart, no lateral differentiation. Ventral ala absent. Somatic setae of different sizes (4–19 µm long; Fig. 5A ), set out in eight longitudinal rows in anterior one fifth of body length and in six longitudinal rows along rest of body except on tail, where they are irregularly arranged.

Annulated head region with annulations completely surrounding amphid ( Figs 6 A–C, 7C); in some specimens, there is a seemingly non-annulated head region, but some partial annulation of the dorsal and ventral sides of the head can be observed ( Fig. 7 A–B); both forms are considered annulated head regions, even though the degree of annulation differs between the two morphotypes. Labial region folded inwards in all specimens. Six papilliform outer labial sensillae and four cephalic setae, 44–57% cbd long, situated at or slightly posterior to mid-level of amphid. Spiral amphideal fovea, 1.2–1.4 turns, located on a cuticularised amphideal plate ( Figs 6B , 7B ), larger in holotype than in paratype (~0.6 vs 0.4 cbd, respectively; Fig. 4 C–D); amphideal aperture with similar shape to amphideal fovea but tapering proximally (compare Fig. 6A and 6B ).

Buccal cavity small, with small dorsal tooth; subventral teeth not observed ( Fig. 6C ). Pharynx muscular, slightly swollen at anterior extremity, and with pyriform bulb at posterior extremity. Nerve ring at 60– 62% of pharynx length. Secretory-excretory system not observed. Cardia short.

Reproductive system monorchic, with single anterior testis situated to the right of intestine, 53–63 µm long, outstretched and opposed. Mature sperm small, globular, 2–3 × 3–5 µm. Short, arcuate spicules tapering distally; well-developed capitulum and broad velum ( Fig. 4H ). Small, plate-shaped gubernaculum without crurae. Four pre-cloacal supplements consisting of short setae on broad bases ( Fig. 4I ), 23–45 µm apart, beginning 15 µm anterior to cloaca. Tail conical, with three small caudal glands and spinneret.

Female

Similar to males. Female reproductive system didelphic, amphidelphic with reflected ovaries situated either to the right or left of intestine, with anterior and posterior ovaries always situated on opposite sides. Vulva located slightly post median. Cuticular pars distalis vaginae and pars proximalis vaginae surrounded by constrictor muscle. Mature eggs 66–73 × 25 µm.

Remarks

Stygodesmodora confusa sp. nov. can most easily be differentiated from the other two species of the genus by the location of the cephalic setae at mid-level of amphids (vs anterior to amphids in S. bacillicauda and S. epixantha ). S. confusa sp. nov. also differs from S. bacillicauda in the presence of pre-cloacal supplements (absent in S. bacillicauda ) and the absence of lateral crurae on the gubernaculum (present in S. bacillicauda ), and from S. epixantha by the presence of numerous long somatic setae (short somatic setae in S. epixantha ).

Stygodesmodora confusa sp. nov. closely resembles species of other desmodorid genera, and distinguishing it from these other species requires careful examination of the head region. S. confusa sp. nov. resembles Echinodesmodora moensi Verschelde & Vincx, 1996 in the absence of a cephalic capsule, numerous long somatic setae, and cephalic setae at or slightly posterior to mid-level of amphids, but can be differentiated from the latter by the absence of pharyngeal lumen cuticularisation (present in E. moensi ), amphid shape (<1.25 turns vs 1.5–2.0 turns in E. moensi ), presence of setose precloacal supplements (absent in E. moensi ), and the absence of knotty protrusions on the tail (present in E. moensi ). The most important distinction, however, is the presence of an amphideal plate in S. confusa sp. nov. This species is also superficially similar to species of Bolbonema , i.e., B. brevicolle ( Cobb, 1920) , B. longisetosum (Jensen, 1985) comb. nov., and B. spiralis Hourston & Warwick, 2010, in the presence of both short and long somatic setae, cephalic setae just posterior to mid-level of amphid, and in the structure of the copulatory apparatus. The amphideal plates in S. confusa sp. nov. give a swollen appearance to the head region laterally (see Fig. 7A ), and in some specimens there is a gap in the body annulations in the head region (compare Fig. 7A and 7C ), which may be wrongly interpreted as a nonannulated head region or even a head capsule. S. confusa sp. nov., however, is clearly defined by an annulated region, and not a head capsule, because (1) the swollen part of the head is mostly restricted to the area surrounding the amphids (i.e., the amphideal plates), (2) the cuticle is the same thickness in head and body regions (see Fig. 6C ), and (3) annulations are present dorsally and ventrally at least to mid-level of amphids, with one continuous annulation anterior to the amphid (see Figs 6B , 7 A–C). The genus Bolbonema , however, is characterized by a globular head capsule (i.e., conspicuously thicker cuticle and absence of annulations; Verschelde & Vincx 1996; Verschelde et al. 1998).

Figures

Fig. 4. Stygodesmodora confusa sp. nov. A. Anterior body region of female. B. Male head (holotype). C. Male head (paratype). D. Male head (holotype). E–F. Anterior body region of female. G. Female posterior body region. H. Right spicule and gubernaculum. I. Male copulatory apparatus. Arrows show position of pre-cloacal supplements. Scale bar: A–D = 30 µm, E–G = 36 µm, H = 20 µm, I = 40 µm.

Fig. 5. Stygodesmodora confusa sp. nov. A. Entire male. B. Female reproductive system. Scale bar: A = 50 µm, B = 36 µm.

Fig. 6. Stygodesmodora confusa sp. nov., light micrographs of female. A. Head region showing amphideal aperture. B. Head region showing amphideal fovea. C. Head region showing buccal cavity. D. Vulva. Scale bar: A–C = 15 µm, D = 18 µm.

Fig. 7. Stygodesmodora confusa sp. nov. Scanning electron micrographs. Female head (three different specimens). Scale bar = 5 µm.