Lithobius (Ezembius) ternidentatus sp. n. (Lithobiomorpha, Lithobiidae), a new species from China

Abstract Lithobius (Ezembius) ternidentatussp. n. (Lithobiomorpha, Lithobiidae), recently discovered from Wuyuezhai Mountain, Lingshou County, Shijiazhuang City, Hebei Province, China, is described. Morphologically it resembles L. (E.) multispinipes Pei, Lu, Liu, Hou, Ma & Zapparoli, 2016, but can be easily distinguished from the latter by having a different sized Tömösváry’s organ, different numbers of ocelli, obvious differences in ventral plectrotaxy of legs 14, and tarsal articulation ill-defined on legs 1–13, well-defined on legs 14–15. The main morphological characters of the known Chinese species of the subgenus Ezembius Chamberlin, 1919 based on adult specimens is presented.


Introduction
Ezembius was originally proposed as a subgenus of Lithobius Leach, 1814 in the family Lithobiidae by Chamberlin (1919); it accommodates a group of 60 species/subspecies mostly known from Asia, with little extension into north-western North America. Known species colonize a wide range of habitats, from the Arctic and Subarctic to tropical and sub-tropical forests, to steppe and overgrazed stony areas of central Asia, to Himalayan montane forests, from the sea shore up to 5500 m (Himalayas) (Zapparoli andEdgecombe 2011, Qiao et al. 2018). Although the subgenus was formally proposed as new and described in 1923 (Chamberlin 1923), according to Jeekel (2005) its name had been already validated in 1919 (Chamberlin 1919). Ezembius is characterized by antennae with ca 20 articles; ocelli 1+4-1+20; forcipular coxosternal teeth usually 2+2; porodonts generally setiform, sometimes stout. Tergites are generally without posterior triangular projections; tarsal articulation of legs 1-13 is distinct. Female gonopods are with uni-, bi or tridentate claws, and 2+2-3+3 (rarely 4+4) spurs (Zapparoli and Edgecombe 2011).
The myriapod fauna of China is still poorly known and very little attention has been paid to the study of Lithobiomorpha, with only 82 species/subspecies hitherto known from the country. Altogether, 21 species of Ezembius have been recorded from China, but none of them have been reported from Hebei Province (Pei et al. 2018, Qiao et al. 2018. Here a new species, recently found in the Hebei Province, China, is described and illustrated. Tables of the main morphological characters of Chinese Ezembius species are presented.

Materials and methods
All specimens were hand-collected under leaf litter or stones. The material was examined with the aid of a Motic-C microscope (Xiamen, China). The colour description is based on specimens preserved in 75% ethanol, and the body length is measured from the anterior margin of the cephalic plate to the posterior margin of the postpedal tergite. Type specimens are preserved in 75% ethanol and deposited in the School of Life Sciences, Hengshui University, Hengshui, China (HUSLS). The terminology of the external anatomy follows Bonato et al. (2010).

Taxonomy
Material examined. Holotype: ♀ (Fig. 1) Colour: antennal articles and whole body pale yellow-brown, tergites darker, pleural region and sternites pale yellow with greyish hue; basal and proximal parts of forcipules, forcipular coxosternite, and SS XIV and XV darker.
Antennae: 22-25 articles, commonly 24 articles (Fig. 1A), 2 specimens 22+24, 3 specimens 24+25 articles; antennae articles length is approximately equal to width except basal articles II-V slightly longer than wide, distal-most article 2.7-3.1 times as long as wide; abundant setae on the antennal surface, less so on the basal articles, gradual increase in density of setae to about the fourth article, then more or less constant.
Cephalic plate smooth, convex, slightly wider than long; tiny setae emerging from pores scattered very sparsely over the whole surface; frontal marginal ridge with shallow anterior median furrow; short to long setae scattered along the marginal ridge of the cephalic plate; lateral marginal ridge discontinuous, posterior margin continuous, straight, wider than lateral marginal ridge (Fig. 1A).
Five or six oval to rounded ocelli on each side (Fig. 1B), most of them rounded, domed, translucent, usually darkly pigmented, situated in two irregular rows; the posterior two ocelli comparatively large; others subequal in size.
Tömösváry's organ situated at anterolateral margin of the cephalic plate, about same size as the largest two ocelli and lying well apart from them (Fig. 1B).
All tergites smooth, without wrinkles, dorsum slightly convex; tiny setae emerging from pores scattered sparsely over the entire surface, near the margin with few long setae; T I narrower posterolaterally than anterolaterally, generally trapezoidal, narrower than the cephalic plate and T III, obvious shorter than T III, the cephalic plate slightly wider than T III. Lateral marginal ridges of all tergites continuous. Posterior margin of TT I, III, V, and VII slightly concave, posterior marginal ridges continuous. Posterior margins of TT VIII, IX, XI, XIII, and XV concave, posterior marginal ridges discontinuous. Posterior angles of tergites generally rounded, without triangular projections. Miniscule setae scattered sparsely over the surface, 3-5 slightly thick and long setae on anterior and posterior angles of each tergite.
Posterior side of sternites narrower than anterior side, generally trapezoidal, smooth; setae emerging from sparsely scattered pores on the surface and lateral margin, few long setae on the surface of the anterior part of each sternite, 1-2 comparatively long setae scattered sparsely on the surface respective both of the middle part and posterior part of each sternite.
Legs robust, tarsal articulation ill-defined on legs 1-13, well-defined on legs 14-15; all legs with fairly long curved claws; legs 1-13 with anterior and posterior accessory spurs; anterior accessory spurs moderately long and slender, forming a moderately small angle with the claw, posterior accessory spurs slightly more robust, forming a comparatively large angle with the claw, legs 14 and 15 only with small posterior accessory spurs; long setae sparsely scattered over the surface of prefemur, femur and tibia of all legs, more setae on the tarsal surface; setae on dorsal surface of tarsus slightly shorter than the ventral, one row of thicker setae regularly arranged on the medial ventral side of tibia of legs 1-13, with setae significantly reduced in legs 14 and 15, no thicker setae regularly arranged in one row on the medial ventral side of tibia; legs 14 and 15 moderately thicker and longer than the anterior pairs in the female; leg plectrotaxy as in Table 1.
Female S 15 anterior margin broader than posterior, generally trapezoidal, posteromedially straight, colour yellow-brown; short to long sparse setae evenly scattered on surface; surface of the lateral sternal margin of genital segment well chitinized, posterior margin of genital sternite deeply concave between condyles of gonopods, except for a small, median tongue-shape bulge; relatively long setae sparsely scattered over ventral surface of the genital segment; gonopods: first article fairly broad, bearing 8-10 moderately long setae, arranged in three irregular rows; with 2+2 moderately long and slender, coniform spurs, inner spur slightly smaller than the outer; second article with 5-6 long setae, arranged in two irregular rows; third article with 3-4 comparatively long setae, arranged in one or two irregular rows; third article with a simple apical claw (Fig. 1D).
Male S 15 posterior margin narrower than anterior, posteromedially straight, sparsely covered with long setae on the surface; sternite of genital segment smaller than in female, usually well sclerotized, posterior margin deeply concave between the gonopods, without medial bulge; long setae sparsely scattered on the ventral surface of the genital segment, fewer setae near S 15, fringed with longer setae along the posterior margin; gonopods short, appearing as a small hemispherical bulge, with 1-3 long setae, apically slightly sclerotized (Fig. 1E).
Habitat. The specimens here studied were collected in a mixed coniferous broadleaved forest at ca 480-900 m above sea level, in moderately moist habitats under roadside stones and litter of the forest floor.  Etymology. The specific name ternidentatus refers to the coxosternite anterior margin with 3+3 slightly acute triangular teeth.
Discussion. The new species resembles L. (E.) multispinipes Pei, Lu, Liu Hou, Ma & Zapparoli, 2016 from the Xinjiang Autonomous Region in having 3+3 prosternal teeth commonly, the posterior two ocelli comparatively large, coxal pores 3-5 and with two coniform spurs on female gonopods. However, the new species can be easily distinguished by the following characters: the Tömösváry's organ about same size as the largest ocellus in contrast to slightly smaller than the adjoining ocelli in L. (E.) multispinipes; and with five or six ocelli in new species instead of eight ocelli in L. (E.) multispinipes; and tarsal articulation ill-defined on legs 1-13 in the new species in contrast to well-defined on legs 1-13 in L. (E.) multispinipes; and legs 14 posterior accessory spur absent versus present in L. (E.) multispinipes, moreover, the 14 legs ventral plectrotaxy are obviously different: 0-1-3-2-2 compared to 0-1-3-2-1 in L. (E.) multispinipes.
To assist in the identification of the Chinese species of Lithobius (Ezembius), the main morphological characters (Table 2) of the known Chinese species of the subgenus Ezembius Chamberlin based on adult specimens are presented.