Scutisotoma robustodens Huang & Potapov, 2012, sp. nov.

Scutisotoma robustodens sp. nov.

Figs 19–26, Tab. 1

Material. Holotype, adult female, Russia (East Siberia), Irkutsk District, Slyudyanka, shore of Baikal Lake, on moistened big stones, leg. M. Potapov, 29.viii.2008. Paratypes, 5 specimens, the same locality as for holotype. Paratypes: adult and subadult females. Type specimens deposited in MSPU.

Description. Size from 0.8 to 1.1 mm. Colour dark, black. Cuticle weakly reticulated. 8+8 ocelli, G and H smaller (Fig. 22). PAO elliptical, not constricted; as long as 1.2–1.5 ocellus diameter and as 0.6–0.7 U3. Maxillary outer lobe with 4 sublobal hairs and simple maxillary palp. Maxillary head with short, unmodified lamellae. Labral formula as 3/5,5,4. Labium with 5 papillae (А–Е), papilla Е with 6 guards (e7 absent), 3 proximal and 4 basomedian chaetae. One available small juvenile specimen with 5 guards at papilla E. Ventral side of head with 3+3 postlabial chaetae. 11 (more rarely 10) chaetae on Ant.1. Ant.1 with 2 basal microsensilla (bms), dorsal and ventral, and 2 ventral sensilla (s), Ant.2 with 3 bms and 1 laterodistal s, Ant.3 with 1 bms and 5 distal s (including 1 lateral), guard sensilla of AO as long as inner ones (Fig. 23). Sensilla on Ant.4 weakly differentiated, subapical organite small.

Dorsal axial chaetom of Th.II–Abd.III as 7–8,5/4–5,4–5,4–5. Common chaetae of normal shape, on dorsal side of Abd.V some of macrochaetae and common chaetae slightly serrated (Fig. 26). Thorax without ventral axial chaetae. Macrochaetae differentiated only laterally on Th.II–III and on two last abdominal segments, medial ones on Abd.V about as long as 0.3–0.4 of tergal midline. Sensilla on tergites clearly differentiated, shorter than ordinary chaetae. Sensillar formula as 3,3/2,2,2,2,4 (s), 1,1/1,1,1 (ms). Sensilla on Abd.I–III in mid-tergal position. Microsensillum on Abd.I–II in front of lateral sensillum, on Abd.III in front of and between medial and lateral sensilla, their arrangement as in S. subarctica (Fig. 56 B in Fjellberg 2007). On Abd.V medial pair of sensilla 1.5 as long as lateral pair, all sensilla of subequal width (Fig. 26).

Unguis simple without inner tooth (Fig. 24). Ti.1–3 with 21–21–24(23) chaetae, correspondingly. B-row of chaetae on Ti.1–2 complete. Tibiotarsal tenent chaetae (1,2,2) clearly clavate, long (U3: t.ch. = 0.5–0.6). Femur 1 with 4–5 a -chaetae, 1 ae -chaeta, 2 e -chaetae, and 6 chaetae of pe-p-pi-i -group (Figs 1–2). Upper and lower subcoxa with 2 and 5−6 chaetae on Leg 2 and 3−4 and 5−6 on leg 3. Ventral tube with 3+3 laterodistal and usually with 4 posterior chaetae. Tenaculum with 4(3)+4(3) teeth and 2 chaetae. First proximal teeth of tenaculum smaller and sometimes absent. Anterior furcal subcoxae with 13–18, posterior ones with 6 chaetae. Furca rather short. Anterior side of manubrium with a pair of distal chaetae (Fig. 25), posterior side with 16–18+16–18 (including 4+4 on laterobasal lobes) (Fig. 21). Dens distally with 3, more rarely 2, anterior chaetae, posterior side of dens with weak dorsal humps and 5–6 chaetae (Figs 19–20). Mucro massive, with 3 teeth, lamellae absent. Ratio of manubrium: dens: mucro = 5.4–5.7: 2.1–2.4: 1.

Affinity. The species belongs to subarctica group by having simple maxillary palp, 3 prelabral chaetae, and reduced number of guards on labial papilla E. By chaetotaxy of dens (2–3/5–6) the new species is placed in intermediate position between S. subarctica (Gisin, 1950) (6–7/7–8) and S. indigirka Potapov, Babenko & Fjellberg, 2006 (1/3–4). In distal chaetotaxy of ventral tube (3+3) S. robustodens sp. nov. is more similar to the former species.

Distribution. Known only from the type-locality.

Name derivation. The new species is named after the stout dens.