Lithobius (Ezembius) tetraspinus, a new species of centipede from northwest China (Lithobiomorpha, Lithobiidae)

Abstract Lithobius (Ezembius) tetraspinus sp. n. (Lithobiomorpha: Lithobiidae), recently discovered from Hami City, Xinjiang Autonomous Region, NW China, is described. Morphologically this species resembles L. (E.) sibiricus, Gersfeldt, 1858, but is distinguishable by a different coxal pore formula, absence of accessory spurs on leg 15, morphology of the second article of the female gonopod, and legs 14 plectrotaxy. A table of the main morphological characters of Chinese Lithobius (Ezembius) species is presented.

The myriapod fauna of China is still poorly known and very little attention has been paid to the study of Lithobiomorpha, with only 74 species/subspecies hitherto known from the country (Ma et al. 2014a(Ma et al. , b, 2015Minelli et al. 2016;Pei et al. 2014Pei et al. , 2015Pei et al. , 2016Qin et al. 2014). Xinjiang Autonomous Region is among the poorly studied regions of China with only eight species at present registered from its territory (Ma et al. 2014 b;Pei et al. 2015Pei et al. , 2016. Altogether, 18 species of Lithobius (Ezembius) have been recorded from China, only three of them from Xinjiang Autonomous Region. Here with a new species recently found in Balikun County is described.

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 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). The following abbreviations are used throughout: Etymology. The specific name refers to the second article of the female gonopods with four short, robust spines lying dorsally on the posterior part of the external margin.

Diagnosis.
A Lithobius (Ezembius) species with body length 9.6-13.3 mm, antennae composed of 19-22 articles, commonly 20+20; 8-10 ocelli on each side, arranged in 3 irregular rows, posterior two ocelli comparatively large; Tömösváry's organ small, subequal in size to the adjoining ocelli; 2+2 coxosternal teeth; porodonts moderately thick, posterolateral to the lateralmost tooth; posterior angles of all tergites without triangular projections; coxal pores 2-5, oval to round; female gonopods commonly with 3+3 moderately large, coniform spurs; second article of female gonopods with four short, robust spines lying dorsally on the posterior part of the external margin; gonopods with a simple terminal article; male gonopods short and small, with 1-2 long setae on the terminal segment.
Colour: basal antennal articles chocolate, distal articles gradually lighter, distalmost article yellow-brown. Tergites yellow-brown, TT 1 and 14 more darker. Cephalic plate and T 15 chocolate. Pleural region pale grey. Sternites pale yellow-brown. Distal part of forcipules red-brown, with basal and proximal parts of forcipules and forcipular coxosternite and sternite 15 yellow-brown. Legs 1-13 pale yellow-brown with greyish hue, legs 14 and 15 red-brown, tarsi of legs yellow-brown.
Antennae: 19-22 articles, commonly 20+20 ( Fig. 1), only one specimen 20+25 articles; basal article longer than wide, second article markedly longer than wide, with following articles gradually shortening distally. Distalmost article 2.0-2.4 times as long as wide. Abundant setae on antennal surface, gradual increase in density of setae basally to distally to approx. 3-4 th article.
Cephalic plate smooth, convex, tiny setae emerging from pores scattered sparsely over the entire surface. Frontal marginal ridge of head with shallow anterior median furrow. Setae of various lengths scattered along the marginal ridge of the cephalic plate. Lateral marginal ridge discontinuous. Posterior margin continuous, straight ( Fig. 1).
Eight to ten oval to rounded ocelli on each side (Fig. 2), arranged in three irregular rows; posterior two ocelli large; ocelli adjacent to the Tömösváry organ slightly small. Seriate ocelli domed, translucent, usually darkly pigmented.
Tömösváry organ at anterolateral margin of the cephalic plate, moderately smaller, subequal in size to the adjacent ocelli ( Fig. 2-To).
Coxosternite subtrapezoidal (Fig. 3), anterior magin narrow, lateral margins of the coxosternite slightly longer than medial margins. Median diastema moderately deep, V-shaped; anterior margin with 2+2 subtriangular slightly acute teeth. Porodont thick and strong, just posterolateral and separated from the lateral tooth, hardly bulged at base (Fig. 3). Scattered short setae on the ventral side of coxosternite, longer setae near the dental margin, more longer setae near the porodont. Forcipules and forcipular coxosternite without obvious special modifications. 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 1 narrower posterolaterally than anterolaterally, generally trapezoidal, narrower than the cephalic plate and T 3, cephalic plate slightly wider than T 3. Lateral marginal ridges of all tergites continuous. Posterior marginal ridges of TT 1 and 3 slightly concave, continuous, posterior marginal ridges of TT 5, 8, 10, 12 and 14 shallow concave, discontinuous. Posterior angles of tergites generally rounded, without triangular projections. Miniscule setae scattered sparsely over the surface, more numerous setae on anterior and posterior angles of each tergite, with 2-4 long setae on anterior angles and 2-3 long setae on posterior angles of each tergite.
Sternites smooth, trapezoidal, posterior side narrower than anterior. Setae emerging from sparsely scattered pores on the surface, a pair of approximate symmetrically arranged long setae on both anterior part and posterior part of each sternite. The setae obviously increase in number on S 15, scattered evenly over the surface.
Legs robust, tarsal articulation ill-defined on legs 1-13, well defined on legs 14-15. All legs with fairly long curved claws. Legs 1-14 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. Dense glandular pore on the surface of prefemur, femur, tibia, and tarsi of legs 14 and 15. Leg pair 15 lacking accessory spurs. Long setae sparsely scattered over the surface of prefemur, femur, tibia, and tarsi of legs 1-13; more setae on the tarsal surface, many thicker setae scattered evenly over the tarsal surface, setae arranged in one row on the ventral surface of tarsi of legs 1-13, with setae significantly reduced on legs 14 and 15, no thicker setae and setae arranged in one row on the ventral surface of tarsi present. Legs 14 and 15 slightly thicker than the anterior pairs in the female, tarsus 1 3.7-4.7 times as long as wide in legs 15. Legs 15 significantly thicker and stronger than the anterior pairs in the male, with a central longitudinal discontinuous shallow groove on the dorsal of femur, and a black vertical line at the bottom; tarsus 1 3.8-4.3 times as long as wide in legs 15. Leg plectrotaxy as in table 1.
Coxal pores 2-5, round or slightly oval, variable in sizes, arranged in a row; usually 4555, 4554, rarely 3454, 3455, 3343 in females and 2332, 2333 in males. Coxal pore field set in a relatively shallow groove, the coxal pore-field fringe with prominence. Prominence with short to moderately long setae sparsely scattered over the surface.
Male. S 15 posterior margin narrower than anterior, posteromedially slightly convex, sparsely covered with long setae, more than the anterior; sternite of genital segment obviously smaller than the female, usually well sclerotized; posterior margin deeply concave between the gonopods, without medial bulge. Long setae 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 1-2 long setae, apically slightly sclerotized (Fig. 7).   Pei et al., 2015Takakuwa, 1939Takakuwa, 1940Pei et al., 2016Zapparoli 1991Attems, 1934Attems, 1927Takakuwa & Takashima, 1949Pei et al., 2011  Female. S 15 anterior margin broader than posterior, generally trapezoidal, posteromedially slightly convex. Short to long setae sparsely scattered on S 15 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 linguliform bulge. Relatively long setae scattered over ventral surface of the genital segment, few setae near S 15. Gonopods: first article fairly broad, bearing 23-30 short to moderately long setae, arranged in four irregular rows; with 3+3, few 3+4, only one 4+4 moderately long and slender, coniform spurs, inner spur slightly smaller than the outer (Fig. 4); second article with 8-12 long setae, arranged in three irregular rows, with three long setae and four short, robust spines lying dorsally on the posterior part of the external margin; third article with 4-6 long posteroventral setae, and two short, robust spines lying dorsally on the posterior part of the external margin (Fig. 5). Third article of female gonopods with a simple apical claw with a very small subtriangular blunt denticle on the inner margin (Fig. 6).
Remarks. The new species with 2+2 coxosternal teeth, 9-10 ocelli on each side of head, female gonopods with 3-4 moderately large, coniform spurs, and leg pair 15 lacking accessory spurs, is morphologically similar to Lithobius (Ezembius) sibiricus Gerstfeldt, 1858 from Mongolia and Russia, but is readily distinguished by having coxal pores arranged in a 2-5-formula in contrast to L. (E.) sibiricus with a coxal pore formula 5-8; the second article of the female gonopods with four short, robust spines lying dorsally on the posterior part of the external margin versus with eight short, robust spines lying dorsally on the posterior part of the external margin; lacking accessory spurs on legs 15 th versus having small accessory spurs on legs 15 th ; moreover, leg 14 plectrotaxy is distinctly different, 10311 (dorsal) and 01321 (ventral) compared to 10311 (dorsal) and 01332 (ventral).
Habitat. The specimens were collected in a Larix forest at 950-1000 m alt. It inhabits moderately moist habitats under roadside stones and litter of the forest floor.
To assist in the identification of the Chinese species of Lithobius (Ezembius), the range and main morphological characters of the known species of the subgenus in the area is presented (table 2). These characters are specific only to adults of the taxa occurring in China.