Subisotoma erratica, 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 : 25-27

Subisotoma erratica sp. nov.

Figs 64–76 , Tab.2

Type material. Holotype, female, Russia, Siberia, southern parts of Chelyabinsk Province, Arkaim, steppe, 18.v.2000, leg. L. Zalish ( MSPU). Paratypes: 1 female, 2 males, 1 juv, from the same sample as holotype; 22 specimens, Kazakhstan, 40 km from Arkalyk, Tasty River, 08.vi. 1983; 49 specimens, Russia, Siberia, Khakasia, vicinity of Shira [54° 29’N 89° 58’E], Shira lake, under wormwood, 21.vi.1990; 5 specimens, same region, mountainous stony steppe, 21.vi.1990; 4 specimens, same region, Itkul’ lake, meadow, 22.vii.1990; 7 specimens, same region, Iris association, 22.vii.1990; 6 specimens, Tuva, Tsuger–Els, sand, Artemisia , 12.vii.1993, all leg. S. Stebaeva ( MSPU).

Other material. 5 specimens, Altai Republic, Ust'–Kansk District, 10 km E Karakol, 1100 m alt., steppic slope, 27.vii.2008. leg. V. Kadnikov ( MSPU).

Description. Size 0.6–0.9 mm. Colour light greyish-blue, with numerous lighter spots over the whole body. Cryptopygy less developed than in species of the ‘ pusilla’ group ( Fig. 76 ). Cuticle with fine and relatively uniform granulation, primary hexagons form hexa- or orthogonal structure ( Fig. 71 ). Ocelli 8+8, H and G smaller, can be almost invisible ( Fig. 70 ). PAO large and wide, about 2.5 as long as nearest ocellus and subequal to inner unguis ( Fig. 70 ). Maxillary outer lobe with simple palp and 4 sublobal chaetae. Labral formula as 2/554. Labium with all papillae A–E present, papilla Е with five guard chaetae ( Fig. 72 ). Proximal and basomedian fields of labium with 3 and 4 chaetae, respectively. Ventral side of head with 4+4 postlabial chaetae. Ant.1 with 2 basal microsensilla (bms, dorsal and ventral), and 2 thick ventral sensilla (s) differing in size. Ant.2 with 3 bms and 1 laterodistal s. Ant.3 with 1 bms (may be absent in juveniles) and 5 distal s ( AO and one lateral s), both the inner and outer sensilla of AO widened, inner ones almost roundish. Additional sensilla absent ( Fig. 74 ). Ant.4 with many poorly differentiated sensilla, subapical organite small, microsensillum present.

Dorsal axial chaetom of Th.II–Abd.III as 7,6/4–5,4–5,5. Thorax without ventral axial chaetae. Macrochaetae slightly differentiated, visible laterally on thorax and on abdominal tip. Macrochaetae of Abd.V 0.33–0.45 as long as tergite length. Sensilla clearly differentiated, shorter than ordinary chaetae. Sensillar formulas 33/22224 (s) and 10/100 (ms). On Abd.I–III the sensilla situated immediately in front of the p-row of chaetae. On Abd.V the lateral pair of sensilla shorter than medial and widened ( Fig. 64–65 ).

Unguis simple and slightly broadened basally, without inner tooth. Unguiculus shorter than inner edge of unguis. Ti.1–3 with 21, 21, 22–23 chaetae ( Figs 66–68 ). Tibiotarsal tenent chaetae hardly differentiated, pointed, shorter than inner unguis (0.8–1.0). Ventral tube with 4+4 laterodistal and 4 caudal chaetae. Tenaculum with 3+3(2) teeth and one chaeta. Sterna of Abd.III with or without a pair of medial chaetae isolated from the main setaceous part of segment ( Fig. 69 ). Anterior furcal subcoxae with 7–8 chaetae, posterior ones with 6–7. Manubrium without anterior chaetae, posterior side with 9–11+9–11 chaetae, laterobasal lobes with additional 3 chaetae ( Fig. 69 ). Dens with 1 anterior and 4(3) posterior chaetae arranged as 2 basal, 1 at middle, and 1 subapical, the shortest basal chaetae often absent in subadult individuals ( Figs 73, 75 ). Mucro short, set off from dens, with two subequal teeth, subapical tooth strong. Ratio of manubrium: dens: mucro = 7–10: 3–6: 1. Anal lobes with three minute setulae.

Affinity. Microsensillar formula (10/100), the presence of anterior chaeta on dens and bms on Ant. 3 are used to separate S. erratica sp. nov. from the other two species of the ‘ asiatica ’ group. From S. asiatica it also differs by having finer cuticular granulation. The small size, 8+8 ocelli, the shape and chaetom of furca show its similarity to the American Folsomides teres Christiansen & Bellinger which differs in the number of chaetae on VT (3+3/2) and fused (?) Abd.V–VI. The systematic position of F. t e re s is unclear and further studies are necessary to assign it to genus as it may be an unusual Folsomides , a representative of Scutisotoma (related to S. montana , S. stepposa , or S. baica ), of Ballistura (veletensis –group) or belonging to Subisotoma .

Distribution. An Asian steppe species being widespread in Kazakstan and southern regions of Siberia.

Name derivation. The new species inhabits Asian steppes, in earlier times inhabited by nomadic tribes (Latin ‘ erraticus ’ means nomadic, wandering).

Figures

FIGURES 64 – 68. Subisotoma erratica sp. nov.: 64 – 65, chaetotaxy of Abd. III – VI (64) and Abd. I – II (65); 66 – 68, distal half of legs 3 (66), 2 (67), and 1 (68).

FIGURES 69 – 76. Subisotoma erratica sp. nov.: 69, ventral chaetotaxy of Abd. II – V (tenaculum not shown); 70, ocelli and PAO; 71, fine structure of cuticle; 72, labial palp (only e-guard chaetae shown in details); 73, dens and mucro, lateral view; 74, Ant. 3, dorsal view; 75, dens and mucro, posterior view (subadult male); 76, profile of three last abdominal segments.