Subisotoma pomorskii, 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 : 11-13

Subisotoma pomorskii sp. nov.

Figs 3 , 17–23 , Tab. 2

Type material. Holotype, male, European part of Russia, Kalug Province, State Reserve “Kaluzhskii zaseki”, broad-leaved forest, 2004, summer, leg. M. Shashkov ( MSPU). Paratypes: 5 females, 2 males, 4 juv., the same data as the holotype ( MSPU).

Other material. 3 specimens, Ukraine, Zakarpat’e, Vynogradiv, beech forest, litter and soil, 23.v.1987, leg. I. Kaprus’ (LPM, MSPU); male, Poland, Bialowieza Park, 10.ix.1994, leg. A. Fjellberg (AF). 1 specimen, Hungary ( SMNG).

Description. Size about 0.7 mm. Colour dark, greyish-black, with numerous lighter spots. Cuticle granulation relatively uniform, pits small and hardly differing from large hexagons (more visible on posterior part of head) ( Fig. 21 ). Ocelli 8+8, H and G clearly smaller ( Figs 19–20 ). PAO wide elliptic, without constriction, about 1.5–2.0 as long as nearest ocellus diameter and slightly shorter than inner unguis (0.9:1). 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, proximal part with 3 chaetae, basomedial field of labium with 4 chaetae. Ventral side of head usually with 4+4(3–5) 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 one lateral, ‘inner’ sensilla of АО clearly broadened. Dorsal side of Ant.3 with 2–4 additional sensilla ( Figs 22– 23 ). Ant.4 with numerous poorly differentiated sensilla, subapical organite small, microsensillum present. All terga with dense cover of short, uniform chaetae, macrochaetae almost undeveloped. Macrochaetae on Abd.V 0.2–0.3 as long as tergite length. Dorsal axial chaetom of Th.II–Abd.III as 8–9,7/6,5–6,6–7. Tergal sensilla fine and long, only slightly shorter than ordinary chaetae. Sensillar formulas 33/23334 (s) and 10/101 (ms) ( Figs 3 , 17 ). On Abd.I–III medial sensilla set slightly in front of p-row of chaetae. Sterna of Th.III with (1)2+2 chaetae.

Unguis slightly broadened basally, inner tooth usually inconspicuous. Ti.1–3 with 21–23–(24)25 chaetae. Ti.1–3 with 1, 2, 2 clearly clavate tenent chaetae, longer than inner edge of unguis (U3: t.ch. = 0.6). Chaetae x and B5 on Ti.3 not modified (only unreproductive males were seen). Ventral tube with 4+4 lateral and (4)5–6 posterior chaetae. Tenaculum with (2)3+3 teeth and one chaeta. Anterior furcal subcoxae with 8–12 chaetae, posterior ones with 6–8. Manubrium without anterior chaetae, posterior side with 8–10+8–10 chaetae, laterobasal lobes usually with 3 chaetae. Dens with 1 anterior and (3)4 posterior strong chaetae. Mucro narrow and rather long, with 2 teeth, not clearly set off from dens ( Fig. 18 ). Ratio of manubrium: dens: mucro = 4.8– 6.2: 3.1–3.8: 1. Each anal lobe with 3 tiny equal setulae.

Affinity. S. pomorskii sp. nov. differs from the majority of known species in the genus by the macrosensillar formula. The new species is most similar to S. quadrisensillata Gao et al. 2009 , recently described from south eastern Asia. The latter differs by having 4 (versus 3 in S. pomorskii sp. nov.) sensilla on Abd.IV and 4–9 (versus 2–4) additional sensilla on Ant.3. European S. pusilla which is at least partly sympatric to S. pomorskii sp. nov. differs having more thoracic sensilla (44/33334 versus 33/ 22–3334 in S. pomorskii sp. nov.). Their ecological and geographical segregation calls for further study.

Variability. Specimens from Ukraine and Poland slightly differ from the above description always having only 4 posterior chaetae on the VT which is rare in specimens from the type locality. In addition, Ukrainian specimens possess a distinct tooth on the unguis and one specimen bears only 2 sensilla on both Abd.I and Abd.II (s. 33/22334 as a whole). Chaetae x and B5 on Ti. 3 in a single reproductive male from Poland are clearly modified. We treat all these populations as a single species.

Distribution. Broad-leaved forests of Eastern Europe.

Name derivation. We dedicate this species to our friend and colleague Jacek Pomorski.

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 17 – 23. Subisotoma pomorskii sp. nov.: 17, chaetotaxy of Th. III, Abd. I and II; 18, dens and mucro, lateral view; 19 – 20, ocelli and PAO, two views; 21, fine structure of cuticle near ocelli D and H; 22 – 23, Ant. 3, dorsal view (variation).