Subisotoma quadrisensillata, Gao, Yan, Xiong, Yan & Potapov, Mikhail, 2009

Gao, Yan, Xiong, Yan & Potapov, Mikhail, 2009, Checklist of Chinese Isotomidae (Collembola) and a description of a new Subisotoma, Zootaxa 2242, pp. 55-63 : 59-62

Subisotoma quadrisensillata sp. nov.

Type material. Holotype: Female (subadult), China, Hainan province, near Qiongzhou channel, Dongzhaigang (N 19 º 51 ′ – 20 º 1 ′, E 110 º 32 ′ – 110 º 37 ′), Red Forest ( Rhizophoraceae g. sp.), litter and soil from 0–15cm depth, 23.i. 2004, leg. Yan Xiong ( SIPPE). Paratypes: 4 females (subadult), from the holotype sample ( SIPEE), 5 females, 2 males, 4 juveniles, from Southern Vietnam, Province Dong Nai, ca. 100 km NE of Ho Chi Minh (Saigon), Cat Tien National park (N 11 º 25 ′, E 107 º 20 ′), deciduous wood, November, 2005, leg. Yu. Shveenkova ( MSPU).

Other material: 1 female (subadult), China, Hainan province, Jianfengling (N 18 º 42 ′, E 108 ° 49 ′), tropic rain forest, ca 1500 m alt., litter and soil from 0–15cm depth, 14.iv. 2004, leg. Yan Xiong ( SIPPE).

Description. Body length up to 0.9 mm. Colour dark, greyish-blue, with lighter spots, darker on dorsal side ( Fig. 14). Cuticle granulation fine, with pits scattered among normal hexagons. Ocelli 8 + 8, G and H smaller and less distinct. PAO elliptic, without constriction, about 1.5–2.0 as long as diameter of nearest ocellus and slightly shorter (0.85–1.0) than inner margin of unguis 3 ( Fig. 2). Maxillary palp simple, four sublobal hairs present. Labrum with 2 / 554 chaetae. Labium with all papillae A–E present, papilla E with 6 guards (e 7 absent), proximal chaetae 3. Basomedial field of labium with 4 chaetae. Ventral side of head usually with 4 + 4 (3–5) postlabial chaetae. Ant.I with 2 bms, dorsal and ventral, and 2 ventral sensilla (s), Ant.II with 3 bms and 1 distal s, Ant.III with 1 bms, 2 inner s, 2 outer s, 1 lateral s, and 4–9 additional s (encircled on Fig. 1). Inner sensilla of АО clearly broadened. Ant.IV with numerous poorly differentiated sensilla, subapical organite small, microsensillum present.

All tergites with a dense cover of short, uniform chaetae, macrochaetae not developed, the longest chaetae on Abd.V 0.22–0.27 as long as tergal length. Dorsal axial chaetom of Th.II–Abd.III as 8–11,7 / 5–6,5 – 6,6–7. Tergal sensilla fine and long, only slightly shorter than ordinary chaetae. Sensillar formulas 33 / 23344 (s) and 10 / 101 (ms). Th.II–III without sensilla near hind corner of setaceous part of tergite. On Abd.I–III the medial sensilla set slightly in front of the p-row of chaetae ( Figs 8–13). All sensilla on Abd.V subequal ( Fig. 13). Additional sensilla absent. Ventral side of Th.I and Th.II without chaetae, Th.III with (1) 2 + 2 chaetae ( Fig. 3).

Unguis slightly elongated, inner tooth usually invisible ( Fig. 4). Ti.I–III with 21, 23–24, 23 – 25 chaetae, respectively. Tibiotarsal tenent chaetae 1,2, 2, clavate, 1.3–1.5 as long as inner edge of unguis. In reproductive males chaetae x and B 5 on Ti.III modified, stick-like, not broadened. Ventral tube with 4 + 4 laterodistal and 4 posterior chaetae. Tenaculum with (2) 3 + 3 teeth and one chaeta. Anterior furcal subcoxae with 8–12, posterior ones with 6–8 chaetae. Manubrium without anterior chaetae, posterior side with 8–11 + 8–11 chaetae and 4 + 4 on laterobasal lobes ( Fig. 7). Dens with one anterior and (3) 4 posterior strong chaetae. Mucro narrow and rather long, with 2 teeth, not clearly set off from dens ( Figs 5, 6). Ratio of manubrium: dens: mucro = 4.0–6.8: 2.8–4.0: 1. Such a high variance reflects the variance of mucro length and its indistinct separation from dens. Each anal lobe with 3 tiny equal setulae.

Affinities. The genus Subisotoma Stach, 1947 was not recorded in China before. Basing on chaetotaxy of furca, number of ocelli, 1,2, 2 tenent hairs, 2 + 2 ventral chaetae on Th.III, and other characters the new species is similar to the common European species S. pusilla (Schäffer) . Our study of S. pusilla from France (Harroque and Lot, leg. L. Deharveng), Poland (Sudetes, leg. D. SkarŻyński), and Ukraine (L’viv Province, leg. I. Kaprus’) has shown that it clearly differs from S. quadrisensillata sp. nov. having different numbers of sensilla on body tergites (44 / 33334 versus 33 / 23344) and additional sensilla on Ant.III (3 (rarely 4) versus 4– 9). The disproportional set of sensilla on Abd.I–IV (2334) found in S. quadrisensillata sp. nov. is unique character unknown for the species of the family Isotomidae . The third sensillum on Abd.IV (encircled on Fig. 12) is especially important to define this species.

Several species (mostly undescribed) with a pusilla -like furca and ventral chaetae on Th.III have been found by us in the materials from Eastern Europe and Asia. Their descriptions and comparison with the new species will be presented in a future publication.

Distribution. SE China (Hainan) and Vietnam.

Derivatio nominis. The species bears four sensilla on each side of Abd.IV.