Neodiplopeltula incisa ( Southern, 1914 ), 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 : 7-13

Neodiplopeltula incisa ( Southern, 1914) gen et. comb. nov.

Figs 1–4 ; Table 2

Diagnosis (based on combined data)

Neodiplopeltula incisa gen. et comb. nov. is characterised by a 1.52–2.24 mm long body; refractive plates underlying cephalic cuticle around amphids present, irregular in shape, not joined, 28–33 µm long and 21–25 µm wide; cephalic setae 8–14 µm long; amphidial fovea 22–28 µm long and 5.5–7 µm wide; oral opening 1–3 µm from anterior end, posterior to cephalic setae bases; secretory-excretory pore located opposite to posterior part of pharynx; tail 2.5–3.9 anal body diameters long; vagina with epiptygmata; spicules 66–79 µm long.

Material examined

SWEDEN: 4 ♀♀, 3 ♂♂, Skagerrak, 58°12′37″ N, 11°18′53″ E, shells and sand at a deep of 15–22 m, 10 Oct. 2012, O. Holovachov leg. (SMNH-169255); 1 ♀, 1 ♂, Skagerrak, 58°20′21″ N, 11°12′42″ E, coarse shell sand at a deep of 14–17 m, 19 Aug. 2014, O. Holovachov leg. (SMNH-169258).

Description

Adult

Body cylindrical, posteriorly tapering in tail region, straight or weakly ventrally curved upon fixation. Cuticle finely transversely striated along entire body as seen under SEM (striation can be observed under LM but very fine and shallow and cannot be measured with confidence), except for visually smooth labial region and terminal part of tail; longitudinal striation not observed under the light microscope, but distinct under the scanning electron microscope, covers cuticle over entire body length. 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 irregular in shape (with incised edges), not connected with each other on ventral and dorsal sides. Inner labial sensilla small pore-like, located on anterior surface of lips, discernible under SEM only. Outer labial sensilla papilliform, located on anterior surface of lips, clearly visible under SEM only. Cephalic sensilla setiform, bases of dorsosublateral setae located posterior to oral opening. Cervical sensilla papilliform, arranged in four sublateral rows starting at level with middle of amphid and ending at level with posterior edge of refractive plate, two or three per row. Amphids similar in shape and size between sexes: amphidial fovea inverted U-shape with dorsal branch 0.5–3.5 µm longer than ventral branch. Oral opening shifted towards dorsal side of body. Stoma barrel-shaped: 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. Cardia ovoid, almost entirely embedded into intestinal tissue. Secretory-excretory system present; secretory-excretory pore located along ventral body line opposite to posterior 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 cylindro-conical 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 248–280 µm long, situated to either right (n = 1) or left (n = 4) of intestine; posterior genital tube 224–259 µm long, situated to either left (n = 1) or right (n = 4) of intestine. Vulva a 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 162–286 µm long, outstretched and posterior testis 117–162 µm long, reflexed. Spicules paired and symmetrical, strongly curved, with ovoid manubrium and subcylindrical shaft. Gubernaculum plate-like, with pair of strong, closely set caudal apophyses variable in shape ( Fig. 4 C–E). Caudal setae present, several ventrosublateral and dorsosublateral pairs arranged in rows along entire tail length (often difficult to observe).

Remarks

Despite the fact that the original description by Southern (1914) is rather brief, the present population closely resembles the type specimens in most morphological and morphometric features, including the shape of the refractive plates underlying the amphids (described as “shield shaped” with “front and lateral walls are notched”). Spicules are slightly shorter in the type specimens (66 µm vs 75–79 µm in recent specimens).

Figures

Fig. 1. Neodiplopeltula incisa (Southern, 1914) gen. et comb. nov. (SMNH-169255). A. Anterior part of female reproductive system. B. Male tail. C. Female pharyngeal region, optical median section. D. Female anterior end, surface view. E. Male anterior end, surface view. F. Female tail. Scale bar = 20 µm.

Fig. 2. Neodiplopeltula incisa (Southern, 1914) gen. et comb. nov., SEM micrographs. A–C, F–G. ♂. D–E. ♀. A. Male anterior end, semi-apical view, dorsal side to the left. B. Male labial region, semiapical view, dorsal side down (arrows point at inner labial sensilla). C. Male anterior end, right lateral view. D. Vulval region. E. Tail terminus. F. Male cloacal region, lateral view. G. Male cloacal region, ventrosubventral view. Scale bars: A, C–D, F–G = 10 µm; B, E = 2 µm.

Fig. 3. Neodiplopeltula incisa (Southern, 1914) gen. et comb. nov. (SMNH-169255). A. ♂, entire specimen. B. ♀, entire specimen. C. Anterior testis. D. Posterior testis. Scale bars: A–B = 100 µm; C–D = 50 µm.

Fig. 4. Neodiplopeltula incisa (Southern, 1914) gen. et comb. nov. (SMNH-169255). A. Male anterior end, lateral view. B. Female anterior end, lateral view. C. Spicules and gubernaculum. D–E. Variability in the shape of gubernaculum apophyses in the same specimen (arrows). Scale bars = 10 µm.