Sinella whitteni sp. nov.

Figs 1–16, Tab. 1

Type locality. China, Guangxi Province, Yachang Nature Reserve, Huaping, Xia Yan Dong.

Type material. Holotype male and 2 paratypes on slide, 28.v.2007, collected by hand, leg. Franck Brehier (sample n° CHIgx07–28/07): holotype in NJU, 2 paratypes in MNHN. 4 paratypes on slide, 14 in alcohol, 26.v.2007, collected by hand, leg. Franck Brehier (sample n° CHIgx07–26/16): 2 paratypes on slide and 8 paratypes in alcohol in NJU, 2 paratypes on slide and 6 paratypes in alcohol in MNHN.

Description. Body length: 1.4–1.7, up to 2.3 mm.

Habitus and head. Eyes absent. Body colour totally white in alcohol (Fig. 1). Antenna 2.4 times as long as cephalic diagonal. Antennal segments ratio as I: II: III: IV = 1: 1.6–1.8: 1.3–1.6: 2.3–2.9. Antennal chaetae of 5 kinds: ciliated mesochaetae; very thin, rather long, finely ciliated mesochaetae; thin, smooth, acuminate short chaetae; rather long, parallel, thin s-chaetae; short thickened s-chaetae (including the 2 rods of Ant. III organ). Long, smooth chaetae absent on antennae. No apical bulb on Ant. IV.

Labral papillae absent. Prelabral and labral chaetae 4/5,5,4, all smooth. Lateral process of labial palp thicker than normal chaetae, with tip reaching beyond apex of labial papilla (Fig. 2). Subapical chaeta of maxillary outer lobe thin, subequal to apical one; 3 smooth hairs on sublobal plate (Fig. 3). Labial base as M1,R,E,L1,L2, all smooth; R 0.65–0.80 length of chaeta M1; X, X2 and X4 as ciliate microchaetae; chaeta X3 absent (Fig. 4). Cephalic dorsal chaetotaxy with 5 sutural and 4 macrochaetae in Gr. II (Fig. 5).

S-chaetae by half-tergites from Th. II to Abd. V as 3,2/2,2,3,±14,3.

Thorax. Dorsal thoracic chaetotaxy shown in Fig. 6. Th. II with 5 (m1, m 1i, m2, m 2i, m 2i 2) mediomedian, 2 medio-lateral (m4, m4p), 18–21 posterior macrochaetae and 3 s-chaetae (2 antero-lateral, 1 posterolateral) on each side; p4 as macrochaeta; m 1i and m 2i 2 sometimes absent in juveniles. Th. III with 27–30 macrochaetae and 2 s-chaetae (1 antero-lateral, 1 postero-lateral); m 5i absent; p5 as macrochaeta; m6p as macro- or mesochaeta; p2ep sometimes absent.

Abdomen. Abd. IV 3.9–5.0 times as long as Abd. III along dorsal midline. Abd. I with 7 macrochaetae centrally and 2 s-chaetae laterally; m 2i, a2, a3 and m4p as macrochaetae. Abd. II with 3 dorso-central (m3, m3e, m3ep), one lateral (m5) macrochaetae and 2 s-chaetae. Abd. III with 1 dorso-central (m3), 3 lateral (am6, pm6, p6) macrochaetae and 3 s-chaetae (Fig. 10). Abd. IV with 5 dorso-central (A3, A4, A6, B4, B5), 6 lateral macrochaetae and at least 12 s-chaetae on each side of which 2 short ones, in the middle and posterior part of the tergite, are constant (Fig. 11). Abd. V with numerous chaetae and 3 s-chaetae; m2, m3 and m5 macrochaetae always much larger than others; homology of several chaetae not clear (Fig. 12).

Legs. Trochanteral organ with 19–30 smooth spiny chaetae; 9–13 in the arms of “L” and 10–17 between them (Fig. 7). Tibiotarsal meso- and macrochaetae ciliated, with ciliations not closely appressed to axis; a single smooth straight and acuminate ventro-distal chaeta on hind leg; a tenent hair smooth, pointed, subequal to unguiculus (Fig. 9); an inner outstanding macrochaeta at about 1/3 from tibiotarsus base, ciliate and tapered, 1.5 (tibiotarsus I) to 2 times (tibiotarsus III) longer than inner edge of claw; several inner differentiated chaetae (sensu Chen & Christiansen 1993) slightly thicker and shorter than ordinary chaetae, with shorter cilia (Fig. 8). Claws I and II moderately elongated, claw III normal. Inner basal paired teeth of claw tiny, at 25 – 30% from base of inner edge of claw; distal unpaired tooth absent; 1+1 latero-basal minute teeth, often difficult to see. Unguiculus truncate with outer edge very finely serrated.

Tenaculum with 4 + 4 teeth and one large striate chaeta. Ventral tube anteriorly with 8–10 ciliate chaetae on each side (Fig. 13); posteriorly with 16–28 chaetae of which 6–8 are smooth; each lateral flap with 7 – 8 smooth chaetae with 1 additional ciliate chaeta rarely present (Fig. 14). Manubrium and dentes without smooth outstanding chaetae, manubrium without thick and finely ciliated chaetae (unlike S. trogla). Manubrial plate with 2 pseudopores and 3(4) ciliate chaetae (Fig. 15). Distal smooth part of dens equal to mucro in length (Fig. 16). Mucro bidentate, not elongated, its basal tooth as large as the apical one, with basal spine short, its tip reaching the apex of the subapical tooth (Fig. 16).

Ecology. S. whitteni is the fifth large, strictly troglobitic species of Chinese Sinella, though only moderately modified in relation to cave life. However, the species is likely to be a strict troglobite as we never got it from samples made in humid and dark habitats outside caves, where oculated Sinella are abundant.

Etymology. Named in honour of Tony Whitten for his enthusiastic support of biodiversity surveys and conservation of the caves in southern China.

Remarks. This cave species is most close to S. trogla Chen & Christiansen, 1993, the other cave species of Guangxi, described from a Guilin cave about 370 km from Yachang. They share absence of eyes, cephalic dorsal chaetotaxy, ciliate post-labial chaetae X, X2 and X4, inner differentiated tibiotarsal chaetae finely ciliate, abundant chaetae on each side of ventral tube and chaetotaxy of Abd. I–IV. S. trogla differs from S. whitteni sp. nov. by its much longer antennae (Antenna / cephalic diagonal =3.5-4.3 against 2.4 in S. whitteni; Ant. IV / cephalic diagonal = 2 against 1 in S. whitteni), and by several characters listed in Table 1.

S. whitteni is only moderately troglomorphic, by its rather large size (like the four other troglobitic Sinella of China, and in contrast with non-cave species of the genus), the slight elongation of its claw compared to outside species of the genus and the absence of unpaired inner tooth on it, a character often observed in troglomorphic Entomobryidae .

Ordinary chaetae in Sinella as in many other Entombryidae are only materialized by their socket after specimen mounting. s-chaetae have the same kind of sockets, but as they are less labile, they are usually kept on the body of mounted specimens, which allows to reconstruct their pattern. The number and arrangement of s-chaetae on tergites in this species are stable, and do not vary during postembryonic development except for Abd. IV.

Chaetotaxy of Entomobryidae including s-chaetae (‘setulae’) was first explored by Szeptycki (1972, 1979), in a wide diversity of taxa, but he did not focus on their arrangement as a potential taxonomic character, and most records of s-chaetae in previous literature are incomplete or inaccurate for this family. Schaetotaxy is now used as a powerful tool for the taxonomy of different Collembolan families (Potapov 1989; Deharveng 2004), but its interest in Entomobryidae, Paronellidae and Tomoceridae remains to be assessed.