Paracrobeles kelsodunensis, Boström & Holovachov, 2015

Boström, Sven & Holovachov, Oleksandr, 2015, Description of a new species of Paracrobeles Heyns, 1968 (Nematoda, Rhabditida, Cephalobidae) from Kelso Dunes, Mojave National Preserve, California, USA, European Journal of Taxonomy 117, pp. 1-11 : 3-4

Paracrobeles kelsodunensis sp. nov.

urn:lsid:zoobank.org:act:3D3142CA-44FA-422F-9B6A-8A988B3B75EC

Figs 1–2 , 3 A–C, I; Table 1

Diagnosis

Paracrobeles kelsodunensis sp. nov. is characterised by a body length of 469–626 µm in females and 463–569 µm in males; cuticle coarsely annulated, annuli 3.0– 4.8 µm wide at midbody; lateral field with two wings, each separated by a broad groove, extending almost to tail terminus; three pairs of asymmetrical lips, pairs of lips separated by U-shaped primary axils, with two long guarding processes emerging from the first annule, each lip with four (usually) or three (rarely) tines along its margin: two long acute, with or without one shorter in the middle, and one long acute extending along the secondary axil; three long labial probolae, deeply bifurcated, with slender prongs without tines; metastegostom with a strong, anteriorly directed dorsal tooth; pharynx corpus anteriorly spindle-shaped, posteriorly elongate bulbous with dilated lumen; isthmus narrow, demarcated by a break in muscular tissue: anteriorly with heavy musculature, posteriorly further narrowing with reduced musculature; pharyngeal corpus 2.5– 3.3 times isthmus length; nerve ring and excretory pore at level of metacorpus to metacorpus-isthmus junction; spermatheca 24–87 µm long; postvulval uterine sac 60–133 µm long; vulva in a depression; spicules 33–38 µm long; and male tail with a 5–8 µm long mucro.

Etymology

The new species name refers to the place where it was found.

Material examined

USA: holotype ♀, paratypes 15 ♀♀ and 9 ♂♂, SMNH Type-8715–Type 8720, 28 Mar. 2010, California, Mojave National Preserve, Kelso Dunes , soil around roots of desert plants (34°53.698’N, 115°42.155’W; 34°53.754’ N, 115°42.248’ W and 34°54.226’ N, 115°42.200’ W), legit O. Holovachov & P. De Ley.

Description

Adult

Body variably arcuate when killed by heat. Cuticle coarsely annulated, annuli 3.0– 4.8 µm wide at midbody. Irregular longitudinal striae give the cuticle a tiled appearance. Lateral field with two wings, areolated, each separated by a broad groove, appearing as four incisures under LM, occupying about 20% of body diameter, extending almost to tail terminus in both sexes. Lip region weakly offset, carrying 6 + 4 papillae and two rounded amphid apertures. Three pairs of asymmetrical lips, one dorsal and two ventrolateral. Pairs of lips separated by U-shaped primary axils, with two long guarding processes emerging from the first annule. Each lip with four (commonly) or three (rarely – seen in one specimen so far) tines along its margin: two long acute, with or without one shorter in the middle, and one long acute extending along the secondary axil. Three labial probolae, 13.0– 15.5 µm long, deeply bifurcated, with slender prongs without tines. Stoma about one lip region diameter long. Stomatal parts not clearly discernible. Cheilorhabdia oval in latero-median view; metastegostom with a strong, anteriorly directed dorsal tooth. Pharyngeal corpus anteriorly spindle-shaped, posteriorly elongate bulbous with dilated lumen; isthmus narrow, demarcated by a break in muscular tissue: anteriorly with heavy musculature, posteriorly further narrowing with reduced musculature; bulb oval, with valves. Nerve ring and excretory pore vary in position, from the level of metacorpus to metacorpus-isthmus junction, at 60–68% of neck length and at 57–68% of neck length, respectively. Deirids at level of isthmus, at 69–82% of neck length. Excretory canal cuticularised distally.

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 large, 1.4–3.1 times vulval body diameter (VBD) long. Vagina straight and perpendicular to body axis, about one-third to two-fifths of VBD. Vulva in a sunken area. Intra-uterine eggs 43–66 x 30–36 µm. Tail conoid, generally slightly curved ventrad, curved dorsad in some specimens, with 16–21 ventral annuli, non-annulated in terminal 6–12 µm, terminus minutely rounded. Rectum sigmoid, about half of ABD long. Phasmid openings located at about one-third to two-fifths of tail length.

Male

Similar to female in most respects, except for the sexual characters. Reproductive system monorchic, dextral in position; testis reflexed ventrad anteriorly. Spicules slender, paired and symmetrical, strongly curved ventrad; with oval manubrium and subcylindrical, gradually narrowing shaft. Gubernaculum plate-like. Genital papillae distributed as follows: two pairs ventrosublateral precloacal (at 5–11 µm and at 45–57 µm anterior to cloaca), one pair ventrosublateral adcloacal, a single midventral on anterior cloacal lip; two pairs (one ventrosublateral and one lateral) at midtail; three pairs (one lateral, one subventral and one dorsosublateral) near tail terminus. Phasmid openings located at about two-fifths of tail length, one to two annuli posterior to the lateral midtail papillae. Tail slightly curved ventrad, conoid, with a 5–8 µm long mucro and minutely rounded terminus.

Remarks

The population of Paracrobeles kelsodunensis sp. nov. from Kelso Dunes described here agrees in many respects with the description of P. mojavicus collected from sandy soil in a lava field, Mojave Desert, California. The new species differs from P. mojavicus by having a prominent, anteriorly directed, dorsal metastegostom tooth (vs no metastegostom tooth); a somewhat more anterior position of the excretory pore (at level of metacorpus or metacorpus-isthmus junction vs at level of isthmus); male tail with a 5–8 µm long mucro (vs male tail without mucro). Type specimens of P. mojavicus were examined (see Fig. 3 D–I) and among them, one male ( Fig. 3I ) was found to have a prominent metastegostom tooth. The presence of a metastegostom tooth has not been described for any other species than P. kelsodunensis sp. nov., which might indicate that the population described by Taylor et al. (2004) is a mixture of species. One possible explanation could be a polymorphism based on food sources, and a comparison between molecular characters would probably be needed to resolve the status of the Paracrobeles populations from the Mojave Desert.

Figures

Fig. 1. Paracrobeles kelsodunensis sp. nov. A. Pharyngeal region. B. Female gonad. C. Female tail. D. Male tail. Scale bar = 20 µm.

Fig. 2. Paracrobeles kelsodunensis sp. nov. SEM micrographs. A. Anterior end, left lateral view. B. Anterior end, semi-en face view. C–D. Anterior end, subventral view. E. Vulval region. F. Male tail, ventral view. G. Female tail, right sublateral view (arrow points at phasmid). H. Male tail, left lateral view (arrows point at papillae). I. Male tail, left lateral view (arrow points at phasmid). Scale bars: A–D = 5 µm, E–I = 10 µm.

Fig. 3. A–C. Paracrobeles kelsodunensis sp. nov. LM micrographs. A. Male anterior end, ventral side to the right. B–C. Female anterior end, ventral side to the right. D–H. Paracrobeles mojavicus Taylor, Baldwin & Mundo-Ocampo, 2004. D–F. Female anterior end, ventral side to the right. G–H. Male anterior end, ventral side to the right. I. Paracrobeles cf. kelsodunensis sp. nov., male anterior end, ventral side to the right. Scale bar: A–I = 10 µm.