Subisotoma bisensillata, Potapov, Mikhail, Babenko, Anatoly, Fjellberg, Arne & Greenslade, Penelope, 2009

Potapov, Mikhail, Babenko, Anatoly, Fjellberg, Arne & Greenslade, Penelope, 2009, Taxonomy of the Proisotoma complex. II. A revision of the genus Subisotoma and a description of Isotopenola gen. nov. (Collembola: Isotomidae), Zootaxa 2314, pp. 1-40 : 15-17

Subisotoma bisensillata sp. nov.

Figs 1 , 28, 30–31, 33 , 34–37 , Tab. 2

Type material. Holotype, female, Russia, Far East, Partisansk Province, Przhevalski Mt. Range, vicinity of Ekatirinovka, sample 29: entrance of ‘Letuchaya mysh’ cave, mosses, 25.ix.2004, leg. M. Potapov ( MSPU). Paratypes: 35 specimens, the same data as the holotype; 13 specimens, same region site and data, sample 27R; 2 specimens, same region, Shkotovo Province, Levandiiskii Mt. Range, Khualaza Mt., sample 60: mosses on rock in deep crevice, 02.x.2004; 2 specimens, same region, sample 6: mosses on tree trunks ( Alnus , Betula ), 1100–1200 m alt., 18.ix.2004, leg. M. Potapov ( MSPU).

Description. Size up to 1.0–1.2 mm. Colour dark, almost black, with numerous colourless spots, ventral side lighter. Cuticle with pits (better visible on a head). Ocelli 8+8, H and G clearly smaller ( Fig. 30 ). PAO wide elliptic, without constriction, about twice as long as ocellus diameter and shorter than inner unguis (0.8: 1). Maxillary palp simple with 4 sublobal chaetae. Labrum with 2/554 chaetae. Labium with all papillae A–E present, papilla E with 6 guard chaetae (e7 absent), proximal chaetae 3. Basomedial and basolateral fields of labium with 4 and 5 chaetae respectively. Ventral side of head with 4+4(5) postlabial chaetae. Ant.1 with 2 bms, dorsal and ventral, and 2 ventral sensilla (s), Ant.2 with 3 bms and 1 distal s, Ant.3 with 1 bms and 5 distal s, including 1 lateral in АО. ‘Inner’ sensilla of АО clearly broadened. Dorsal side of the segment with 3(4) additional sensilla ( Fig. 28 ). Ant.4 with numerous poorly differentiated sensilla, subapical organite small, microsensillum present.

All terga with dense cover of short, uniform chaetae, macrochaetae poorly developed. On Abd.V macrochaetae 0.2 times as long as tergite length. Dorsal axial chaetom of Th.II–Abd.III as 9,6–7/5–6,6,7–8. Tergal sensilla shorter and more slender than ordinary chaetae, set slightly anterior to the p-row. Sensillar formulas 33/22224 (s) and 10/101 (ms) ( Figs 1 , 34 ). Ventral side of Th.III usually with 2+2 chaetae ( Fig. 31 ).

Unguis usually toothless. Ti.1–3 with 22, 24, 24–26 chaetae ( Figs 31 , 36 ). Tibiotarsal tenent chaetae 1–2–2, clearly clavate, longer than inner edge of unguis (U3: t.ch. = 0.6–0.7). Chaetae x and B5 on Ti. 3 in males poorly modified. Ventral tube with 4–5+4–5(6) lateral and 5(6) posterior chaetae. Tenaculum with 3+3 teeth and one chaeta. Anterior furcal subcoxae with 9–15, posterior ones with 7–8 chaetae. Manubrium without anterior chaetae, posterior side with 10–11+10–11 chaetae, laterobasal lobes usually with 4 chaetae. Dens with one anterior and 4 posterior chaetae. Mucro narrow and rather long, with 2 teeth and lateral lamella ( Fig. 33 ). Ratio of manubrium: dens: mucro = 4.6–6.4: 2.3–3.6: 1. Each anal lobe with 3 tiny equal setulae.

Affinity. S. bisensillata sp. nov. is most similar to S. tenuis . It differs from the latter by having more chaetae on VT, 2+2 ventral chaetae on Th.III, and more additional sensilla on Ant.3.

Variability. A few specimens found on Kunashir Island (South Kuriles, Far East) differ from above description in having longer tergal sensilla ( Figs 34–35 ) and only 21 chaetae on Ti.1 ( Figs 36–37 ). Because of lack of material from other areas of Far East a decision on the taxonomical status of this form awaits future study.

Distribution. The species is known from several adjacent localities in the mountains of Southern Primor’e (Russian Far East).

Name derivation. The presence of two sensilla on all abdominal terga excepting Abd.V is the main feature distinguishing S. bisensillata sp. nov. from other studied species of the ‘ pusilla ’ group.

Figures

FIGURES 1 – 6. Sensillar chaetotaxy of Subisotoma: 1, Subisotoma tenuis, Subisotoma bisensillata sp. nov. (3,3 / 2,2,2,2,4); 2, Subisotoma guzeriplica sp. nov. (3,3 / 2,2,2,3,4); 3, Subisotoma pomorskii sp. nov. (3,3 / 2,2 – 3,3,3,4); 4, Subisotoma homonomica sp. nov. (3,3 / 3,3,3,3,4); 5, Subisotoma quadrisensillata (3,3 / 3,3,3,4,4); 6, Subisotoma pusilla (4,4 / 3,3,3,3,4).

FIGURES 28 – 33. Subisotoma bisensillata sp. nov. (28, 30 – 31, 33) and Subisotoma tenuis (29, 32): 28 – 29, Ant. 3, dorsal view; 30, ocelli; 31, chaetotaxy of leg 3 and sterna of Th. III; 32, chaetotaxy of sterna of Th. III and ventral tube; 33, dens and mucro.

FIGURES 34 – 37. Subisotoma bisensillata sp. nov. (34, 36) and Subisotoma cf. bisensillata (35, 37): 34 – 35, chaetotaxy of three last abdominal segments; 36 – 37, apical part of leg 1 (additional chaeta of D-row encircled).