Scutisotoma tenuidentifera, Potapov & Babenko & Fjellberg, 2006

Potapov, Mikhail, Babenko, Anatoly & Fjellberg, Arne, 2006, Taxonomy of the Proisotoma complex. Redefinition of genera and description of new species of Scutisotoma and Weberacantha (Collembola, Isotomidae), Zootaxa 1382 (1), pp. 1-74 : 39-41

Scutisotoma tenuidentifera sp.n.

Figs. 103–108

Type material. Holotype: ♀, Russia, Tuva, Eastern Tanny-Ola Mts. Range, Tes-Khemskii region, vicinity of village Shuurmak (50 o 38’N, 95 o 19’E), cliffs in petrophyte steppe, under lichen Rhysoplaca sp., 12.viii.1997, leg. N. Sidelnikova. Paratypes: 7 exx., same sample. 6 exx., same locality and site, under Lecanora argopholis, Aug. 1995 , leg. S. Stebaeva. 6 exx., Russia, Tuva, Tes-Khemskii region, Aryskannyg-Khem , stony river bank, 15.vii.1993, leg. S. Stebaeva. 3 exx., Russia, Tuva, 7 km south from village Seserlig (51 o 48’N, 94 o 15’E), southern steppe slope with Sedum , 29.vi.1990, leg. S. Stebaeva ( MSPU) .

Other material. 19 exx. from the following samples: Russia, Tuva, Eastern Tanny- Ola Mts. Range, Picea-Larix forest, on tree bark. Russia, Siberia, Krasnoyarsk Territory, village Nazarovo (56 o 00’N, 90 o 22’E), steppe-meadow. Russia, Siberia, Khakasia, 5 km from Birik-Chyul (53 o 19’N 89 o 52’E), on cliffs under Draba spp. , Sedum , all leg. S. Stebaeva. Russia, Siberia, Chita Province, Dauria Ononskaya, river Onon, village Nizhnii Tsasuchei (50 o 30’N, 115 o 07’E), near water, leg. O. Berezina ( MSPU).

Description. Size 0.7–1.0 mm. Colour spotted dark-violet, extremities slightly paler. Cuticle with fine but visible primary granulation. Ocelli 8+8, G and H smaller. PAO wide elliptical, not constricted, about as long as unguis (0.8–1.0 of U 3). Maxillary outer lobe with 4 sublobal hairs, maxillary palp bifurcate. Maxillary head with short, unmodified lamellae. Labral formula 4/554. Labium with a full set of papillae and guards. Proximal field with 3 chaetae, basomedian field with 4. Ventral side of a head usually with 4+4 postlabial chaetae. Ant.1 with 2 basal microsensilla (bms, dorsal and ventral) and 2 ventral sensilla (s). Ant.2 with 3 bms and one laterodistal s, Ant.3 with one bms and 5 distal s (AO and one lateral s). Lateral guards of AO thinner and slightly longer than the inner pair of sensilla. Additional sensilla on Ant. 2–3 in males hardly differ in size from ordinary chaetae. Sensilla on Ant.4 hardly differentiated, subapical organite small.

Axial chaetom of Th.II–Abd.III as 7–8,6/4–5,4–5,5. Thorax without ventral axial chaetae. Macrochaetae differentiated laterally on Th.II–III and on tip of abdomen, medial ones on Abd.V are 0.3–0.4 as long as tergite. Sensilla on tergites clearly shorter than ordinary chaetae. Sensillary formula 33/22224 (s) and 11/111 (ms). Medial sensillum on Abd.III in posterior quarter of the tergite. On Abd.V the adjacent sensilla of medial and lateral pairs (accp2 and accp3) set close together, the sensilla of lateral pair (accp3 and accp4) longer and moved slightly forward ( Fig. 108 ).

Unguis simple, without inner tooth. Number of chaetae on Ti.1–3 similar to basic set (21–21–25), Ti.3 sometimes with 1–2 additional proximal chaetae. B-row on Ti.1–2 with 7 chaetae. Chaetae x and B 5 on Ti. 3 in male stick-like, sometimes slightly widened on tip. Tibiotarsal tenent chaetae (1-2-2) usually clavate, of variable length, about as long as unguis (U 3: t.ch. = 0.8–1.3: 1). Ventral tube with 4+4 laterodistal and 5–6 posterior chaetae. Tenaculum usually with 3+3 teeth (rarely one additional small tooth may be present) and one chaeta. Anterior furcal subcoxa with 11–17 chaetae, posterior one with 6–8. Anterior side of manubrium with a pair of distal chaetae, posterior side with 12–16+12–16 on the main part and with (3)4+4 chaetae on the laterobasal lobes. Dens usually with 7 (6–8) anterior chaetae, basal 1/2–1/3 devoid of chaetae ( Fig. 104 ). Posterior side of dens crenulated, usually with 7 chaetae (4 basal and 3 distal, Fig. 104 ). Mucro with two strong teeth, large specimens usually have an additional small tooth on the outer lamella ( Figs. 105–107 ). Ratio of manubrium: dens: mucro = 4.1–6.5: 3.7–4.8: 1.

Intraspecific variability. Variation in the number of mucronal teeth is striking in this species. The third, tiny tooth is regularly absent or present only as a small rudiment. Possibly the same condition occurs in the sibling pair oirota / fjellbergi . Specimens from the Khakasia and Krasnoyarsk Territories ( Fig. 105 ) differ from Tuva specimens by having only 6 posterior chaetae on dens (outer lateral chaeta absent, inner one set closer to basal group). Specimens from the Chita Province also differ in chaetotaxy on posterior side of dens in having the lateral chaetae set closer to medial part of dens. Also the third mucronal tooth is not observed in Chita specimens.

Affinity. S. tenuidentifera sp.n. is most similar to S. ananevae (Babenko & Bulavintsev) , having principally the same furca and tenaculum. S. tenuidentifera is usually distinguished by the presence of a third mucronal tooth, only one lateral sensillum on Ant.3, and different position of sensilla on Abd.V. From S. acorrelata sp.n., described below, it differs by the presence of the third mucronal tooth and the number of chaetae on posterior side of dens (6–7 in tenuidentifera , 10–11 in acorrelata ).

Distribution. Southern Siberia (Tuva, Khakasia, south of Krasnoyarsk Territory, Chita).

Name derivation. The new species is named after tiny tooth on outer lamella of mucro.

Figures

FIGURES 103–108. Scutisotoma tenuidentifera sp.n. 103, 104, dens, specimen from Aryskannyg- Khem (103) and Birik-Chul (104); 105–107, mucro, specimens from Nizhnii Tsasuchei (105), Nazarovo (106), and Aryskannyg-Khem (107); 108, chaetotaxy of Abd.V, Nazarovo (s1–4: accp1–4 sensilla).