Description of a new species of Paracrobeles Heyns , 1968 ( Nematoda , Rhabditida , Cephalobidae ) from Kelso Dunes , Mojave National Preserve , California , USA

A new species of Paracrobeles, P. kelsodunensis sp. nov. is described from the Kelso Dunes area, Mojave National Preserve, southern California. Paracrobeles kelsodunensis sp. nov. is particularly characterised by a body length of 469–626 μm in females and 463–569 μm in males; lateral fi eld with four incisures, extending almost to tail terminus; three pairs of asymmetrical lips, separated by U-shaped primary axils with two long guarding processes, each lip usually with four tines along its margin; three long labial probolae, deeply bifurcated, with slender prongs without tines; metastegostom with a strong anteriorly directed dorsal tooth; pharyngeal corpus anteriorly spindle-shaped, posteriorly elongate bulbous with dilated lumen; spermatheca 24–87 μm long; postvulval uterine sac 60–133 μm long; vulva in a sunken area; spicules 33–38 μm long; and male tail with a 5–8 μm long mucro. The generic diagnosis is emended on the basis of recently described species and a key to the species of Paracrobeles is provided.


Results
Phylum Nematoda Diesing, 1861 Class Chromadorea Inglis, 1983Order Rhabditida Chitwood, 1933Family Cephalobidae Filipjev, 1934 Genus Paracrobeles Heyns, 1968 Type species Paracrobeles laterellus Heyns, 1968 Diagnosis (emended after Holovachov et al. 2009) Cuticle annulated, without distinctly annulated internal layer; annuli with longitudinal striation (tessellated). Lateral field with two wings (three or four incisures), ending near tail terminus in females and in males. Lip region weakly offset, consisting of six lips arranged in three pairs: one dorsal and two subventral. Pairs of lips separated by primary axils with one or two acute triangular guarding processes; secondary axils shallow. Cephalic probolae with three or four long and slender tines. Labial probolae deeply bifurcated without tines along the slender prongs. Six outer labial and four cephalic papilliform sensilla arranged in a cephaloboid manner. Amphidial aperture rounded, located on lateral lips. Stoma divided into cheilo-, gymno-and stegostom: cheilostom barrel-shaped, with strongly sclerotized bacilliform cheilorhabdia; gymnostom narrow tubular, as wide as stegostom, with weakly sclerotized plate-like gymnorhabdia; stegostom consists of a funnel-shaped prostegostom and variably shaped mesostego-, metastego-and telostegostom parts. Metastegostom tooth absent or present. Pharynx cephaloboid: pharyngeal procorpus cylindrical; metacorpus elongate bulbous; lumen of metacorpus often expanded to a large triradiate chamber with seemingly sclerotized lining; isthmus narrower than metacorpus; basal pharyngeal bulb oval, with strongly developed valves. Nerve ring encircling metacorpus, metacorpus-isthmus junction or anterior part of isthmus. Excretory pore opens at level of nerve ring. Deirids present. Female reproductive system cephaloboid; posterior part of ovary straight and relatively short; spermatheca present; postvulval uterine sac present; vulva flat with contour of body or in a depression; vagina straight or directed anteriad. Male reproductive system cephaloboid; spicules cephaloboid, with corpus and manubrium of approximately equal width; gubernaculum plate-like; cornua crurum absent. Male genital papillae: two ventrosublateral pairs located anterior to cloaca; one ventrosublateral pair located just posterior to cloacal opening; two pairs located at middle of tail length; and three pairs (lateral, subventral and subdorsal) near tail terminus; there is a midventral papilla on anterior cloacal lip. Rectum short (about as long as anal body diameter). Phasmid openings located at about one-third to half of tail length in both sexes. Female tail conoid, straight or slightly arcuate ventrad, tail terminus pointed or finely rounded; male tail conoid, slightly arcuate ventrad, tail terminus finely rounded.

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

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, European Journal of Taxonomy 117: 1-11 (2015) 4 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. 3D-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.    3.4 3.2±0.2 (2.9-3.7) 3.2±0.2 (2.9-3.6) c 9.5 10.0±0.6 (9.1-11.5) 9.6±1.0 (8.  Abolafia et al., 2014). * Measured from the illustrations or calculated from other measurements; ** times the corresponding body diameter; -indicates that data are not applicable; 1 Abolafia et al. (2014); 2 Heyns (1968); 3 Rashid et al. (1990); 4 Taylor et al. (2004); 5 Navarro & Lluch (1999); 6 Orselli & Vinciguerra (2002) Navarro & Lluch, 1999

Discussion
The Mojave Desert and especially the Kelso Dunes seem to be an area with a high diversity of species of the family Cephalobidae Filipjev, 1934. Representatives of this family are mostly terrestrial and bacteria-consuming nematodes with a worldwide distribution. They seem to be especially diverse and abundant in deserts, and sand dunes appear to be a suitable habitat for cephalobids. About ten new species have been described from the Mojave Desert, which might indicate a hot spot for cephalobid diversity (De Ley 2014). Hitherto one new genus and six new species, including the one described here, and one already known species have been described from the Kelso Dunes (Boström & Holovachov 2012, 2013a, 2013b. Some of the new species described from the Mojave Desert are closely related, which might further indicate that speciation processes are going on in this area. Species of the genus Paracrobeles are rare inhabitants of terrestrial ecosystems and have a rather restricted distribution. So far they have been found in warm, dry sandy soils in southern Africa (South Africa and Namibia), the Mediterranean (Spain and Italy), California and Iran (Abolafia et al. 2014;Heyns 1968;Navarro & Lluch 1999;Orselli & Vinciguerra 2002;Rashid et al. 1990;Taylor et al. 2004). The description of the new species adds morphological data important for species identification and broadens the diagnosis of Paracrobeles.