Crossodonthina clavata

Ecology. The new species inhabits the litter of the studied forests.

Description. Body length: holotype 2.5 mm, paratypes 1.5 – 2.6 mm. Color: red while living and white in alcohol (Fig. 1). Chaetal morphology. Dorsal ordinary chaetae of five types. Long macrochaetae (Ml) weakly serrated and clavated (Figs 3, 8). Short macrochaetae (Mc) morphologically similar to Ml, usually smooth, shorter than Ml. Very short macrochaetae (Mcc) morphologically similar to and shorter than Mc. Mesochaetae (me) similar to ventral chaetae, thin, smooth, and pointed, various in length (Fig. 10). Microchaetae (mi) similar to mesochaetae and about half the length of the shortest mesochaetae (chaetae Oca, Di 2). S-chaetae (s) on terga thin, smooth, usually shorter than or equal to Mc (Fig. 3). Head. Eyes 3 + 3, uncolored, isolated from each other, two on anterior and one on posterior part of tubercle Oc, the anterior two eyes not included in the tubercle. Antenna 4 - segmented (Fig. 4). Ant. I with 9 chaetae. Ant. II with 11 Chaetae. Ant. III dorsally fused to Ant. IV. Guard chaeta sgd of Ant. III slightly migrated distally, two rods exposed in separate pits. Ant. IV dorsally with 8 subequal, slightly thickened and blunt sensilla (S 1 – 8), apical bulb trilobed, organite (or) present. Ventral chaetotaxy of Ant. IV: ap with 5 bs and 9 miA, ca with 1 bs and 6 miA, cm with 1 bs and 9 miA, cp with 16 miA (Fig. 5). On ventral side of Ant. III, Vi, Vc, Ve with 2, 3, 5 chaetae respectively (Fig. 5). Buccal cone developed, labrum truncated, chaetal formula as 0 / 2, 2 (Fig. 9). Labium with 11 chaetae, without papillae x. Mandible hypertrophied and complex (Fig. 6), consisting of 5 fringed rami, 4 teeth and some spine-like chaetae. Three of the 5 rami short, fringed, each ramus with long filaments, the other 2 rami long, developed, with marginal filaments, the 2 long rami about 10 times as long as the shortest one. Maxilla consisting of two lamellae, each lamella with 2 minute apical teeth, without marginal filaments (Fig. 7). Dorsal tubercles and chaetotaxy of head as in Table 1. and Fig. 3. Dorsal central area with 6 tubercles: 1 tubercle Cl, 2 tubercles Oc, 1 tubercle Fr and 2 tubercles An, the tubercle Fr and 2 An stand closely each other. Dorsal posterior area with 4 separate tubercles: 2 Di and 2 De, microchaetae Di 2 and De 2 free from tubercle Di and De. Line of chaetae Di 1 – De 1 crosses line of Di 2 – De 2 on head (cross-type) (Deharveng 1983). Tubercles Dl, L and So on dorsal lateral area fused each other. Ventral chaetotaxy of head. Group Vi with 5 chaetae, groups Vea, Vem and Vep with 4, 3 and 2 chaetae respectively. Thorax (Table 2 & Fig. 3). Th. I with 3 + 3 tubercles, Di, De, Dl with 1, 2, 1 chaetae respectively. Th. II with 4 + 4 tubercles, sensory microchaeta (ms) present on tubercle Dl. Th. III with 4 + 4 tubercles. Chaetotaxy of thorax and legs as in Table 2. Unguis with a basal inner tooth, without unguiculus. Tibiotarsus with chaeta M. Abdomen (Table 2 & Fig. 3). Abd. I – III respectively with 4 + 4 tubercles, tubercle Di, De, Dl and L with 2, 3 (2 + s), 2, 4 chaetae respectively. Abd. IV with 4 + 4 tubercles too, tubercle Di with 2 chaetae, tubercle De with 3 (2 + s) chaetae, tubercle Dl with 3 chaetae, tubercle L with 7 chaetae (6 + s). Abd. V dorsally with 3 + 3 tubercles, two tubercles Di separated, tubercle De usually separate from Dl, rarely De fuse to Dl. Abd. VI with 1 tubercle on each side. VT with 4 + 4 chaetae. Furcular remnant with 4 (3 – 5) chaetae (Fig. 10).

Figures 1, 3 – 10, Tables 1 – 3

Diagnosis. Three uncolored eyes per side on head; cephalic chaeta O present; body tubercles well differentiated; cephalic tubercles Dl, L and So fused each other; mandible with 4 basal teeth and five fringed rami; maxilla with two lamellae and each lamella with two teeth; labral chaetotaxy as 0 / 2, 2.

Remarks. Till now, 13 species of genus Crossodonthina have been reported worldwide, 12 species from Asia and only one from Oceania (Jiang & Zhang 2012, Hu et al., 2019). Four of these have 2 + 2 eyes, and the other 9 species have 3 + 3 eyes. Crossodonthina clavata sp. nov. is the tenth one with 3 + 3 eyes. In general appearance, Crossodonthina clavata sp. nov. is close to C. choui Jiang & Zhang, 2012 in the presence of chaeta O on tubercle Fr, having 4 chaetae on VT, the presence of S chaetae on tubercle L of Abd. IV and having 2 chaetae on each tubercle Di of Th. II – Abd. IV. However, C. clavata sp. nov. can be distinguished from the latter by differences in the arrangement of cephalic tubercles and body chaetotaxy. The former has fused tubercles on head, tubercles Dl, L and So fused each other, and has 4 chaetae (3 + s) on tubercle De of Th. II, versus having separated tubercles on head, tubercle Dl separated from tubercles L and So, and having 5 chaetae (4 + s) on tubercle De of Th. II in the latter. The new species is also similar to C. tridentiens Yue & Yin, 1999 from Shanghai in macrochaetae on terga sheathed, blunt and serrated; tubercle Di on Th. II – Abd. IV well defined; tubercle Oc with 3 chaetae; tubercle Di, De, Dl on Th. I with 1, 2, 1 chaetae respectively; cephalic tubercle Dl fused to L and So; tubercle De on Th. II with 4 (3 + s) chaetae. However, the former can be differentiated from the latter by having 4 basal teeth and 5 rami on mandible, 2 lamellae on maxilla, 1 microchaeta, 1 mesochaeta and 1 macrochaeta on tubercle Oc, 4 (sometimes 3 or 5) chaetae on furcular remnant, versus 3 basal teeth and 4 rami on mandible, 3 lamellae on maxilla, 2 short macrochaetae and 1 long macrochaeta on tubercle Oc, 3 chaetae on furcular remnant. The new species has a unique mandible morphology with 4 basal teeth and 5 rami, that different from all known species of the genus.

Etymology. The name of the species derives from its clavate macrochaetae on terga.

Type material. Holotype: Female, China, Guangdong, Nanling National Forest Park (It is named as “ Mangshan National Nature Reserve ” in Hunan Province), coordinates: 24.927170 N, 112.983979 E, alt. 1645 m, in forest, leg. Ji- Gang Jiang, Yu-Yao Zhao, Fang-Jun Chen. 7. iv. 2018 (J 2018040707). Paratypes: one male, Hunan, Yizhang County, Mangshan National Nature Reserve, in decayed leaves near the entrance of Jiangjunzhai. leg. Ji-Gang Jiang, Yu- Yao Zhao, Fang-Jun Chen. 6. iv. 2018 (J 2018040602) (24.956291 N, 112.955372 E, alt. 1230 m); one male and one female, ibid, in bamboo forest on the sides of highway at Tiantaishan, leg. Ji-Gang Jiang, Yu-Yao Zhao, Fang-Jun Chen. 8. iv. 2018 (J 2018040806) (24.967959 N, 112.957361 E, alt. 1069 m); three females, ibid, in decayed leaves on the side of highway to Xiangsikeng, leg. Ji-Gang Jiang, Yu-Yao Zhao, Fang-Jun Chen. 7. iv. 2018 (J 2018040706) (24.953868 N, 112.974373 E, alt. 1290 m); one female, ibid, in decayed leaves on the side of road at Houwangzhai, leg. Ji-Gang Jiang, Yu-Yao Zhao, Fang-Jun Chen. 7. iv. 2018 (J 2018040702) (24.981000 N, 112.886172 E, alt. 650 m); one male, ibid, in decayed leaves of bamboo on the side of highway at Zeziping, leg. Ji-Gang Jiang, Yu-Yao Zhao, Fang-Jun Chen. 7. iv. 2018 (J 2018040709) (24.944149 N, 112.980348 E, alt. 1506 m). Type materials are housed in the Key Laboratory of Zoology, Hunan University of Arts and Science (HUAS), Changde, Hunan Province, China.