Stegelleta laterocornuta, Boström & Holovachov, 2014

Boström, Sven & Holovachov, Oleksandr, 2014, Descriptions of species of Stegelleta Thorne, 1938 (Nematoda, Rhabditida, Cephalobidae) from California, New Zealand and Senegal, and a revision of the genus, European Journal of Taxonomy 87, pp. 1-19 : 9-10

Stegelleta laterocornuta sp. nov.

urn:lsid:zoobank.org:act:7669B17A-D71A-46C0-8BA0-EB92F28B7111

Figs 1F–J , 3 , Table 2

Stegelleta sp. JB-75 – Nadler et al. 2006: 701, table 1.

Diagnosis

Stegelleta laterocornuta sp. nov. is characterised by a 379–512 µm long body in females and 365–476 µm in males; cuticle divided by regular longitudinal striations into 16 rows of blocks at midbody (excluding lateral field); lateral field with four incisures extending almost to tail terminus in females and to midtail papillae in males, two outer incisures extend to tail terminus in males; three pairs of asymmetrical lips, pairs of lips separated by U-shaped primary axils without guarding processes, secondary axils demarcated by a shallow incisure, each lip asymmetrically rectangular with a smooth margin, only lateral lips have slender acute tines; three labial probolae, bifurcated at half of their length, prongs bent toward one another apically, “snake-tongue”-shaped; pharyngeal corpus 2.3–3.0 times isthmus length; nerve ring and excretory pore at level of metacorpus to metacorpus-isthmus junction, deirids at level of isthmus; vulva without flap; spermatheca 17–31 µm long; postuterine sac 7–24 µm long; spicules 21.5–23.5 µm long.

Etymology

The species name is derived from the Latin lateris (= side) and cornu (= horn), referring to the long acute tine extending along the primary axil on the lateral lips.

Material examined

NEW ZEALAND: holotype ♀, paratypes 13 ♀♀ and 9 ♂♂, SMNH Type-8602 , 1999, South Island, Tasman District, Abel Tasman National Park , legit Christine (Gamble) Powell, cultured as the strain Stegelleta sp. JB-75.

Description

Adult

Body slightly arcuate in different ways when killed by heat, males often strongly arcuate ventrad in tail end. Cuticle coarsely annulated, annuli 1.9–2.7 µm wide at midbody and 2.0– 2.4 µm wide in pharyngeal region. Cuticle tessellated: longitudinal striae giving it a tiled appearance, 16 rows of blocks at midbody (excluding lateral field). Lateral field consisting of two wings separated by a broad groove, appearing as four incisures under LM, occupying about 20–25% of body diameter, extending almost to tail terminus in females and in males. Lip region slightly offset, carrying 6 + 4 papillae and two round amphids. Three pairs of asymmetrical lips, one dorsal and two ventrolateral. Pairs of lips separated by U-shaped primary axils without guarding processes. Each pair with a shallow incisure demarcating a secondary axil. Each lip asymmetrically rectangular with a smooth margin. Lateral lips only with long, slender, acute tine extending along the primary axil. Three labial probolae, 7.0– 8.5 µm high, bifurcated at half of their length, prongs bent toward one another apically (“snake-tongue”-shaped). Stoma somewhat longer than lip region diameter. Stomatal parts not clearly discernible. Cheilorhabdia bacilliform in lateromedian view; metastegostom with a dorsal denticle. Pharynx cephaloboid. Pharyngeal corpus cylindrical; isthmus narrow, often wrinkled, and not clearly demarcated from corpus; bulb oval, with valves. Nerve ring and excretory pore at level of metacorpus-isthmus junction to isthmus. Deirids generally at level of isthmus.

Female

Reproductive system monodelphic, prodelphic, in dextral position in relation to intestine. Ovary reflexed posteriorly at oviduct, ovary straight posterior to vulva. Spermatheca well developed. Postvulval uterine sac about half to one-and-a-half times vulval body diameter long. Vagina about one-third of vulval body diameter. Vulval lips not or slightly protruding, without flaps. Vulva with genital plug seen in one specimen. In four females one intrauterine egg each was found, measuring 36–57 x 14.5–15.5 µm. Tail conoid with 16–22 ventral annuli, terminus broadly rounded or truncate. Phasmids located at about onethird to two-fifths of tail length.

Male

Reproductive system monorchic, dextral in position; testis reflexed ventrad anteriorly. Spicules paired and symmetrical, curved ventrad; with oval manubrium and subcylindrical, gradually narrowing shaft. Gubernaculum plate-like, cornua crurum present. Tail strongly arcuate ventrad, conoid with rounded terminus. The two outer lateral lines extend posterior to the phasmid, transforming into a cuticular ridge that reaches tail terminus. Genital papillae arranged as follows: two pairs subventral precloacal (at 4–6 µm and at 23–28 µm anterior to cloaca), one pair subventral adcloacal, a single midventral papilla on anterior cloacal lip; two pairs (one ventrosublateral and one lateral) at midtail; three pairs (one lateral, one subventral and one dorsosublateral) closer to tail terminus. Phasmids located at about two-fifths to half of tail length.

Remarks

The population of Stegelleta laterocornuta sp. nov. from New Zealand described here agrees in many respects with the descriptions of S. incisa . One major difference is the presence of a long, slender and acute tine extending along the primary axil on the lateral lips. This is a somewhat intermediate stage between S. incisa , which has no tines, and S. arenaria , in which each lip has one acute tine extending along the primary axil. Another difference is the absence of a cuticular flap on the anterior vulval lip, as seen by SEM in the specimens of S. incisa from California.

Figures

Fig. 1. A–E. Stegelleta incisa (Thorne, 1937). A. Pharyngeal region. B. Female gonad. C. Anterior end, surface view. D. Female tail. E. Male tail. F–J. Stegelleta laterocornuta sp. nov. F. Pharyngeal region. G. Female gonad. H. Anterior end, surface view. I. Female tail. J. Male tail. Scale bar = 20 µm.

Fig. 3. Stegelleta laterocornuta sp. nov., SEM micrographs. A. Vulval opening. B. Anal opening. C–D. Anterior end, left subventral view. E. Anterior end, left lateral view (arrows in C–E point at the long acute tine extending along the primary axil on the lateral lips). Scale bars = 2 µm.