Stegelleta incisa ( Thorne, 1937 )

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 : 4-8

Stegelleta incisa ( Thorne, 1937)

Figs 1A–E , 2 , Table 1

Stegella incisa Thorne, 1937: 14–15 , fig. 4G–I.

Stegelleta incisa – Thorne 1938: 65.

Stegelleta ophioglossa – Orselli & Vinciguerra 2002: 216–219, figs 5, 6A–C.

Diagnosis

Stegelleta incisa is characterised by a 465–580 µm long body in females and 428–600 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 and without tines; three labial probolae, bifurcated at half of their length, prongs bent toward one another apically, “snaketongue”-shaped; pharyngeal corpus 2.1–2.9 times isthmus length; nerve ring and excretory pore at level of metacorpus to metacorpus-isthmus junction, deirids at level of metacorpus-isthmus junction to isthmus; vulva with anterior flap; spermatheca 24–43 µm long; postuterine sac 22–36 µm long; spicules 22–36 µm long.

Material examined

USA: 13 ♀♀, 9 ♂♂, SMNH 135940–135942, 28 Mar. 2010, California, Mojave National Preserve, Kelso Dunes, soil around roots of desert plants (34°53.698’ N, 115° 42.155’ W and 34° 53.754’ N, 115° 42.248’ W), legit O. Holovachov & P. De Ley.

Description

Adult

Body slightly arcuate in different ways when killed by heat, males often strongly arcuate ventrad in tail end. Cuticle coarsely annulated, annuli 2.4–3.4 µm wide at midbody and 2.2–3.0 µm wide in pharyngeal region. Cuticle tessellated: longitudinal striae giving it a tiled appearance, each block often with a central indentation as seen under SEM. Anteriorly, 9–10 first annuli, the longitudinal striation is irregular and blocks rounded, followed by a more regular striation creating rectangular blocks, 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 to midtail papillae in males, two outer incisures extend to tail terminus 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, without any tines. Three labial probolae, 8.0– 9.5 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 folded, and not clearly demarcated from corpus; bulb oval, with valves. Nerve ring at level of metacorpus to metacorpus-isthmus junction. Excretory pore and deirids at level of metacorpus-isthmus junction to 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 one to one-and-a-half times vulval body diameter long. Vagina about one-third of vulval body diameter. Vulval lips not or slightly protruding, anterior lip with cuticular flap directed posteriad and partly covering vulval opening. Vulva covered by genital plug in some specimens. Tail conoid with 13–15 ventral annuli, terminus truncate. One specimen has a tail with only 10–11 annuli and broadly rounded terminus. Phasmids located at about one-third to half 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 24–33 µm and at 42–58 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 collected from sand in the Kelso Dunes area, Mojave Desert, California and described here, agrees in many respects with the type specimens of Stegelleta incisa described from Utah by Thorne (1937) and a bisexual population described from Italy by Orselli & Vinciguerra (2002) under the name S. ophioglossa . One major difference is the presence of a cuticular flap on the anterior vulval lip directed posteriad and partly covering the vulval opening, as seen by SEM in the present specimens. This feature is not easily seen with light microscopy, which probably explains why it was not mentioned by Thorne (1937) in his original description. Orselli & Vinciguerra (2002) also did not mention or illustrate it in their specimens, presumably for the same reason.

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. 2. Stegelleta incisa (Thorne, 1937), SEM micrographs.A–B.Anterior end, left lateral view.C.Anterior part of lateral field. D. Deirid (arrow). E. Vulval region. F. Female tail, subventral view. G. Female tail, left sublateral view (arrow points at phasmid). H. Female tail, lateral view. Scale bars = 5 µm.