Figures 1, 3, 5, 7–9, 15, 17, 19, Tables 1–3
Type material. Holotype: female, China, Hunan, Xinning county, Langshan National Geopark. Coordinates: 26.277054N, 110.730618E, alt. 520m, in forest, leg. Ji-Gang Jiang, Cheng Jiang, Li-Ping Duan, 30.iv.2018 (J2018043002). Paratypes: 2 females, China, Hunan, Xinning county, Langshan National Geopark. Coordinates: 26.276580N, 110.729240E, alt. 470m, in forest, leg. Ji-Gang Jiang, Cheng Jiang, Li-Ping Duan, 30.iv.2018 (J2018043003); 3 juvenile, Guangxi, Ziyuan county, Langshan National Geopark, Coordinates: 26.276824N, 110.730528E, alt. 510m, nearby the entrance of the Park, leg. Ji-Gang Jiang, Cheng Jiang, Li-Ping Duan, 29.iv.2018 (J2018042901). Type materials are housed in the Key Laboratory of Zoology, Hunan University of Arts and Science (HUAS), Changde, Hunan Province, China.
Othermaterial. 2females, China, Hunan, Xinningcounty,LangshanNationalGeopark. Coordinates: 26.276986N, 110.736902E, alt. 527m, in forest, leg. Ji-Gang Jiang, Ya-Hui Hu, Wei Hu, 25.vii.2019 (J2019072502).
Diagnosis. 2+2 black eyes on head; labral chaetotaxy as 2/4, 2; cephalic chaeta O present; tubercle Dl on Th. II with 3 chaetae (2+s); mandible with 2 prominent basal teeth and 2 fringed rami of quite different sizes; maxilla with marginal filaments on outer lamella; tubercle Di on Abd. V separated;
Description. Body length: holotype 2.4 mm, two paratypes 2.3–2.4 mm, three juveniles 1.0– 1.1mm.
Color. Red while living (Fig. 1) and white in alcohol (Fig. 3).
Chaetal morphology (Fig. 5). Dorsal ordinary chaetae of five types: Ml (Fig. 5 a–b), Mc (Fig. 5c), Mcc (Fig. 5d), me (Fig. 5 e–f) and mi (Fig. 5h). S-chaetae on terga thin, smooth, shorter than Ml and longer than Mc (Fig. 5g).
Head. Eyes 2+2, black. Antenna 4-segmented (Fig. 15). Ant. I with 9 chaetae. Ant. II with 11 chaetae. Ant. III and IV dorsally fused. Dorsal sensory guard chaeta (sgd) on Ant. III not migrated distally, two rods exposed in separate pit. Ant. IV dorsally with 8 slightly thickened and blunt sensilla, apical bulb trilobed. sensory organite (or) present. Ventral chaetotaxy of Ant. IV: ap with 8 bs and 3 miA, ca with 2 bs and 3 miA, cm with 3 bs and 1 miA, cp without miA. On ventral side of Ant. III, Vi, Vc, Ve with 3, 4, 4 chaetae respectively.
Buccal cone moderately developed. Labrum truncated, chaetal formula as 2/4, 2 (adult) or 4/4, 2 (juvenile). Labium with 11 chaetae and 2 x (Fig. 17). Mandible complicated (Fig. 8), consisting of 2 rami, 2 definite teeth and some spine-like chaetae. Small ramus consisting of one spine-like chaeta and 7–8 slender chaetae, large ramus developed, with 2 rows of marginal chaetae, 4 strong and spine-like chaetae, marginal chaetae on ramus simple, bifurcated or tri-furcated, about 9-12 spine-like chaetae present on the central area of basal part of the large ramus. The longer ramus about 10 times as long as the small one. Maxilla consisting of two lamellae, the inner lamella much shorter than the outer one, with two minute apical teeth, the outer one with marginal filaments on inner side (Fig. 9). On ventral side of head, group Vi with 6+6 chaetae, groups Vea, Vem and Vep with 4, 3 and 2 chaetae respectively. Dorsal tubercles and chaetotaxy of head as in Tab. 1. and Fig. 7. Dorsal central area with 6 separate tubercles; one tubercle Cl, 2 An, one Fr and 2 Oc, chaeta O absent. Dorsal posterior area with 4 separate tubercles: 2 Di and 2 De. Line of chaetae Di2–De2 crosses line Di1– De1 on head (cross-type, Deharveng 1983). Dorsal lateral area with 1 fused tubercle (Dl+L+So).
Thorax (Table 2 & Fig. 7). Th. I with 3+3 tubercles (Di, De, Dl). Th. II and Th. III with 4+4 tubercles respectively, ms on tubercle Dl of Th. II present (its form as in Fig. 5i). Chaetotaxy of thorax and legs as in Table 2. Unguis with a basal inner tooth, unguiculus absent. Chaeta M present on tibiotarsus.
Abdomen (Table 2 & Fig. 7). Abd. I–IV respectively with 4+4 tubercles. Abd. V dorsally with 2+2 tubercles, two tubercles Di close to each other, but not fused together, tubercle De fused to Dl, tubercle L present on ventral side. Abd. VI with 1 tubercle on each side, no cryptopygy. VT with 4+4 chaetae. Furcular remnant with 3-4 chaetae (Fig. 19).
Etymology. The name of the species derives from the locality where it was collected.
Ecology. Among decayed leaves in forest.
Remarks. So far, 12 species of genus Crossodonthina were reported worldwide, 11 species were from Asia and only one from Oceania, seven species were reported from China (Jiang & Zhang, 2012). In genus Crossodonthina, three species have 2+2 eyes, they are C. bidentata, C. hainana and C. montana, the new species is the fourth one with 2+2 eyes. In general appearance, Crossodonthina langshanensis sp. nov. strongly resembles Chinese species C. bidentata (Luo & Chen, 2009) in the number of mandible basal teeth, the arrangement of body tubercles, the presence of chaeta O of tubercle Fr, the number of chaetae on VT, and the presence of inner tooth on claw. However, these species can be distinguished by the following features: structure of mandible (in C. langshanensis with two fringed rami, in C. bidentata with three fringed rami), structure of maxilla (in C. langshanensis outer lamella fringed, in C. bidentate outer lamella not fringed), whether the tubercle Di fused on Abd. V or not (in C. langshanensis not fused, in C. bidentate fused), the labral chaeta formula (in C. langshanensis 2/4, 2, in C. bidentata 2/5, 2), number of chaetae (besides of ms) on tubercles Dl of Th. II (in C. langshanensis 3, in C. bidentata 4). The new species is also similar to the 2+2-eyed Chinese species C. montana (Lee & Kim, 1990) and C. hainana (Xiong et al., 2005) in the arrangement of body tubercles, the presence of chaeta O of tubercle Fr, the separate tubercle Di of Abd. V and the presence of 4+4 chaetae on VT. The new species can be separated from the above species by the characters listed in Table 3.