Neodiplopeltula onusta ( Wieser, 1956 ), 2018

Holovachov, Oleksandr & Boström, Sven, 2018, Neodiplopeltula gen. nov. from the west coast of Sweden and reappraisal of the genus Diplopeltula Gerlach, 1950 (Nematoda, Diplopeltidae), European Journal of Taxonomy 458, pp. 1-34 : 19-24

Neodiplopeltula onusta ( Wieser, 1956) gen. et comb. nov. Figs 8–10 ; Table 4

Diagnosis (based on combined data)

Neodiplopeltula onusta gen. et comb. nov. is characterised by a 0.99–1.48 mm long body; refractive plates underlying cephalic cuticle around amphids present and joined, 32.5–48 µm long and 18.5–24 µm wide; cephalic setae 3–6.5 µm long; amphidial fovea 32–44 µm long and 5–8 µm wide; oral opening 2–5 from anterior end, at level with cephalic setae bases; secretory-excretory pore located opposite to posterior part of pharynx; tail 1.4–2.3 anal body diameters long; vagina with epiptygmata; spicules 52–77 µm long.

Material examined

SWEDEN: 1 ♀, Skagerrak, 58°19′15.6″–20.9″ N, 10°29′33.5″–34.0″ E, soft bottom at a deep of 352–374 m, 10 Sep. 2012, “Inventering Bratten” leg. (SMNH-169284); 1 ♂, Skagerrak, 58°23′00.8″– 22′00.8″ N, 10°20′28.8″–38.3″ E, soft bottom at a deep of 390–428 m, 10 Sep. 2012, “Inventering Bratten” leg. (SMNH-169280); 1 ♂, Skagerrak, 58°28′21.2″–19.2″ N, 10°29′35.6″–43.6″ E, soft bottom at a deep of 248–316 m, 11 Sep. 2012, “Inventering Bratten” leg. (SMNH-169281); 3 ♀♀, 1 ♂, Skagerrak, 58°27′36.7″–43.3″ N, 10°32′52.0″–59.4″ E, soft bottom at a deep of 232–240 m, 12 Sep. 2012, “Inventering Bratten” leg. (SMNH-169282 – SMNH-169283).

Description

Adult

Body cylindrical, posteriorly tapering in tail region, straight or weakly ventrally curved upon fixation. Cuticle finely transversely striated along entire body, except for visually smooth labial region and terminal part of tail (striation can be observed under LM but very fine and shallow and cannot be measured with confidence); longitudinal striation not observed.Somatic sensilla visible along pharyngeal region (cervical setae, see below) and on tail. Labial region bluntly rounded, lips fused. Refractive plates underlying cephalic cuticle around amphids present (periamphideal), extending from level of anteriormost edge of amphid posteriorly some distance behind posteriormost edge of amphid; refractive plates connected with each other on ventral and on dorsal sides. Inner labial sensilla indistinct. Outer labial sensilla papilliform, located on anterior surface of lips. Cephalic sensilla setiform, bases of dorsosublateral setae located at level with oral opening. Cervical sensilla papilliform, arranged in four sublateral rows at level with amphid, one or two per row. Amphids similar in shape and size between sexes: amphidial fovea inverted U-shape with dorsal branch 1.0–2.0 µm longer than ventral branch. Oral opening shifted towards dorsal side of body. Stoma subcylindrical: cheilostom broad; gymnostom barrel-shaped, with weakly cuticularised walls; stegostom short conoid, its lining uniform with lining of pharynx. Pharyngeal tubes absent. Pharynx subcylindrical, muscular, with evenly distributed myofilaments, gradually expanding towards posterior end; not subdivided in distinct sections; pharyngeal lumen uniform in thickness along entire pharynx length; valves absent. Secretory-excretory system present; secretory-excretory pore located along ventral body line opposite to 3/5 th of pharynx; secretory-excretory duct very short, leading from pore to ampulla; renette cell small, its body adjacent and ventral to posterior part of pharynx. Tail conoid with bluntly rounded terminus. Caudal glands opening via three separate subterminal openings, spinneret absent.

Female

Reproductive system didelphic, amphidelphic, ovary branches outstretched and symmetrical, on opposite sides of intestine. Anterior genital tube 109–180 µm long, situated to either right (n = 3) or left (n = 1) of intestine; posterior genital tube 109–145 µm long, situated to either left (n = 3) or right (n = 1) of intestine. Vulva transverse slit, located posterior to midbody. Vagina straight, with developed sphincter muscle surrounding proximal part and distinct epiptygmata in distal part; pars refringens vaginae absent. Sack-like spermatheca present, filled with oval spermatozoa in fertilized specimens. Rectum short.

Male

Reproductive system diorchic, testes opposed; anterior testis outstretched and posterior testis reflexed (poorly discernible in most specimens due to highly granular and dark content of overlapping intestine and cannot be measured). Spicules paired and symmetrical, strongly curved, with elongated ovoid manubrium and subcylindrical shaft. Gubernaculum plate-like, with pair of strong closely set caudal apophyses variable in shape ( Fig. 10 E–G). Caudal setae present, several ventrosublateral and dorsosublateral pairs arranged in rows along entire tail length.

Remarks

The single female used by Wieser (1956) to describe this species has a slightly broader labial region and longer cephalic setae than the population from Sweden, but the specimens described under the name Diplopeltula tchesunovi fill this gap. The position of the oral opening is at level with the cephalic setae bases and the shape of the refractive plates underlying the cephalic cuticle around the amphids (joined along the dorsal and ventral body sides) in both type female and recent specimens are identical and confirm the conspecificity.

Figures

Fig. 8. Neodiplopeltula onusta (Wieser, 1956) gen. et comb. nov. (SMNH-169282). A. Male anterior end, surface view. B. Female anterior end, surface view. C. Female pharyngeal region, optical median section. D. Anterior part of female reproductive system. E. Male tail. F. Female tail. Scale bar = 20 µm.

Fig. 9. Neodiplopeltula onusta (Wieser, 1956) gen. et comb. nov. (SMNH-169282). A. ♀, entire specimen. B. ♂, entire specimen. C. Testes. Scale bars: A–B = 100 µm; C = 50 µm.

Fig. 10. Neodiplopeltula onusta (Wieser, 1956) gen. et comb. nov. (SMNH-169282). A. Male anterior end, lateral view. B. Male stoma, lateral view. C. Female stoma, lateral view. D. Male anterior end, dorsal view. E–G. Variability in the shape of spicules and gubernaculum in different specimens. Scale bars = 10 µm.