Australobiustracheoperspicuus sp. n., the first subterranean species of centipede from southern China (Lithobiomorpha, Lithobiidae)

Abstract Australobiustracheoperspicuussp. n. (Lithobiomorpha: Lithobiidae) was recently discovered from the Cave of the brickyard of Gaofeng village, in the Guizhou Province, southwest China, and it is described here. Morphologically the new species is similar to A.magnus (Trozina>, 1894) from north-western China. The new species can be easily distinguished from those by the trachea connected to the valve of the TIII clearly visible from the dorsal side, the absence of ocelli on each side of the cephalic plate, the DaC spine being only present on the XIIIth–XVth legs. Numbers of examined specimens, distribution and the main morphological characters and an identification key to the known Chinese species of genus Australobius based on adult specimens is given.

The myriapoda fauna of China is still poorly known and this is especially the case with centipedes of the order Lithobiomorpha. Only 80 species/subspecies of lithobiomorphs are to date known from the country (Ma et al. 2014a(Ma et al. , b, 2015Pei et al. 2014Pei et al. , 2015Pei et al. , 2016Pei et al. , 2018Qin et al. 2014Qin et al. , 2017Qiao et al. 2018;Chao et al. 2018). Altogether, only five species of Australobius have been recorded from China (Ma et al. 2008a, b, 2014b, Qin et al. 2014. However, none of them have been recorded from subterranean environment. The present note is devoted to the description of a new cave-dwelling Australobius from southern China, as well as the first subterranean species of Lithobiomorpha from China. An identification key is also given to all six species of Australobius known to occur in China.

Materials and methods
All specimens were hand-collected in cave and preserved in 75 % ethanol. Illustrations and measurements were produced using a ZEISS SteREO Discovery. V20 microscope equipped with an Abbe drawing tube and an ocular micrometer and axiocam 512 color. The colour description is based on specimens fixed in 75% ethanol. The body length is measured from the anterior margin of the cephalic plate to the posterior end of the postpedal tergite. Type specimens are deposited in the School of Life Sciences, Hengshui University, Hengshui, China (HUSLS). The terminology of the external anatomy follows Bonato et al. (2010). Measurements are shown in millimeters (mm).
The following abbreviations are used in the text and the tables: Diagnosis. Antennae with 26 articles, no ocelli, anterior margin of the coxosternite with 5+5 teeth, more or less developed, porodonts slender, between fourth and fifth outer teeth. Tergites without posterior triangular projections, trachea connected to the valve of the T III clearly visible from the dorsal side. Coxal pores 4-6. Tarsal articulation well defined on legs I-XV. No secondary sexual modifications on legs XIV and XV of male. Female gonopods with simple claw, 2+2 spurs. Male gonopods short and small blunt cone bulge, apically slightly sclerotized.
Description. Body length 17.43 -19.24 mm, cephalic plate 1.76-1.93 mm long, 1.77-1.97 mm wide; the whole body pale yellow-brownish, tarsus II of all legs more darker, proximal parts of forcipules and the teeth of the anterior margin of the coxosternite brown, all claws of legs yellow-brown.
Antennae with 26+26 articles; basal article slightly longer than wide, subsequent articles markedly longer than wide, distal article up to 2.5 times as long as wide. Abundant long setae on antennal surface, less so on basal articles, gradual increase in density of setae to about the fourth article, then more or less constant. Length of antenna 7.3-7.4 times width of cephalic plate, and often extending close to posterior edge of T XI ( Figure 1).
No ocelli on each side of the cephalic plate. Tömösváry's organ ovate, situated at anterolateral margin of the cephalic plate ( Figure 2).
Cephalic plate smooth, convex, very slightly wider than long; tiny setae emerging from pores scattered very sparsely over whole surface; frontal marginal ridge with shallow anterior median furrow; from short to long setae scattered along marginal ridge of cephalic plate, there more setae close to the antenna; lateral marginal ridge discontinuous ( Figure 3). Forcipular coxosternite subtrapezoidal (Figure 4), anterior margin broad, external side lightly longer than internal side; median diastema moderately narrow, deeply Vshaped; anterior margin with 5+5 blunt teeth; porodonts slender, lying between the fourth and fifth outer teeth, and more closer to the fourth tooth, the innermost tooth more posterior, and the interdental distance gradually increases from the internal side to the external side ( Figure 5); some short setae scattered on the ventral side of coxosternite; usually there are more setae near the dental margin.
All tergites with wrinkles, central backside slightly hunched, T I posterolaterally narrower than anterolaterally, generally trapeziform, narrower than cephalic plate, broader than T III. Trachea connected to the valve of the T III is clearly visible from continuous; all posterior angles generally rounded, without triangular projections; tiny setae scattered very sparsely over surface, more densely on anterior and posterior angles ( Figure 1). All the tergites more longer than the congeneric species, T X is the longest, at most up to 1.3 times as long as wide.
Posterior side of sternites narrower than anterior one, generally trapeziform, comparatively smooth, long and thick setae emerging from pores scattered sparsely on surface, more setae on surface of the SS I-V (Figure 8), there are two irregular rows short and slightly thinker setae along the posterior margin of the SS VI and VII (Figure 9), few setae on surface of the following SS.
Legs long and slender, tarsal articulation well defined on legs I-IV; all legs with fairly long curved claws; anterior and posterior accessory spurs on legs I-XIII anterior accessory spurs moderately long and slender, forming an angle of about 45° with tarsal claws; posterior one slightly strong, forming an angle of about 30° with tarsal claws; no accessory spurs on legs XIV and XV. Comparatively long setae scattered very sparsely over surface of prefemur, femur, tibia and tarsus of legs I-XIII, more setae scattered on surface of tarsus; dorsal setae slightly longer than ventral, however, more setae in ventral; setae scattered on surface of legs XIV and XV clearly scarcer and short and fine than on other legs. Legs XIV and XV hardly thicker and stronger in both male and female, tarsus I about 6.3-6.6 times as long as wide in legs XV. Tarsus I of legs XV 5.0-5.6 times as long as wide in male, tarsus I of legs XV 5.0-5.6 times as long as wide in male. Leg plectrotaxy as in Table 1.
Female S XV anterolaterally broader than posterolaterally, generally trapeziform, posteromedially straight; sternite of genital segment usually well chitinised; posterior margin of genital sternite deeply concave between condyles of gonopods, except for a small, median bulge; long setae scattered over ventral surface of genital segment, regularly fringed, with longer setae along posterior margin. Gonopods: first article fairly broad, second moderately long and slender, coniform spurs in right, inner spur obviously larger than outer one ( Figure 10); apical claw of third article simple, slender and sharp ( Figure 11). Many long setae on surface of all segments of gonopods.
Male S XV posterolaterally narrower than anterolaterally, posterior edge straight, sparsely covered with long setae; sternite of genital segment smaller than in female, usually well sclerotised. Posterior margin quite deeply concave between gonopods, without a medial bulge; comparatively long setae scattered on ventral surface of genital segment, few slender setae near S XV, setae gradually increasing in density from anterior to posterior, gonopods short and small blunt cone bulge, apically slightly sclerotised (Figure 10).
Etymology. The specific name refers to the trachea connected to the valve of the T III that is clearly visible from the dorsal side.
Habitat. The specimens were collected on the limestone walls and bedrock floor of the cave.
To assist in the identification of the Chinese species of Australobius, numbers of examined specimens, distribution and main morphological characters of the known species of this genus in China is presented (Table 2) and key to the known Chinese species of the genus is presented, these characters are specific only to adults of the taxa occurring in China.
Key to the known Chinese species of the genus Australobius Chamberlin, 1920