Scutisotoma indigirka, 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 : 51-52

Scutisotoma indigirka sp.n.

Figs. 139–142

Material. Holotype: ♀, Russia, Yakutia , Oimyakon Province , middle part of Indigirka river, near Ust’-Nera village. (64 o 33’N, 143 o 13’E), 1600 m alt., northern slope, mosses and lichen on stones, 22.vii.1992, leg. M. Potapov. Paratypes: 15 exx., same sample ( MSPU) .

Description. Size 0.6–0.9 mm. Colour rather light, yellowish-brown, eye spots and apical part of antennae darker. Cuticle with fine primary granulation. Ocelli 8+8, G and H smaller. PAO elliptical, rather wide and not constricted, about 2.0–2.5 as long as ocellus diameter and 0.9–1.3 as long as U 3. Maxillary outer lobe with 4 sublobal hairs and simple maxillary palp. Labral formula 3/554. Labium with all 5 papillae present, papilla E without guard e 7. Proximal field with 3 chaetae, basomedian field with 4. Ventral side of a head with 3+3 postlabial chaetae. Ant.1 with 2 basal microsensilla (bms, dorsal and ventral), and 2 ventral sensilla (s). Ant.2 with 3 bms and 1 laterodistal s, Ant.3 with 1 bms and 5 distal s (AO and one lateral s). Guard sensilla of AO clearly larger than inner pair of sensilla. Additional sensilla on Ant. 2–3 in males not observed. Sensilla on Ant.4 hardly differentiated, subapical organite small.

Dorsal axial chaetom of Th.II–Abd.III as 6–7,6/334. Thorax without ventral axial chaetae. Macrochaetae differentiated only laterally on Th.II–III and on tip of abdomen. Medial macrochaetae on Abd.V are about 0.4 as long as tergite. Sensilla on tergites clearly differentiated, shorter than ordinary chaetae. Sensillary formula 33/22224 (s) and 11/111 (ms). Sensilla on Abd.I–III in mid-tergal position (medial sensillum on Abd.III in posterior 1/3 of the tergite). Microsensillum on Abd.III set close to the lateral sensillum ( Fig. 141 ). On Abd.V the lateral pair of sensilla (accp3 and accp4) clearly thicker and one of them moved anteriorly ( Fig. 142 ).

Unguis simple without inner tooth. Ti.1–3 usually with the basic set of chaetae (21-21- 25). B-row on Ti.1–2 with 7 chaetae. Chaetae x and B 5 on Ti. 3 in males hardly different from other chaetae. Tibiotarsal tenent chaetae (1-2-2) clearly clavate, longer than unguis (U 3: t.ch. = 0.7–1.0: 1). Ventral tube with 4+4 latero-distal and usually with 4 posterior chaetae. Tenaculum with 1–3 chaetae and 4+4 teeth (sometimes one tooth may be absent on one side). Anterior furcal subcoxa with 8–10 chaetae, posterior with 5–6 chaetae. Furca rather short. Anterior side of manubrium with a pair of distal chaetae, posterior side with 11–13+11–13 (including 3+3 on laterobasal lobes). Dens distally with one anterior chaeta, posterior side almost smooth, with 3–4 chaetae ( Figs. 139, 140 ). Retinacular ridges of dens strong. Mucro principally as in S. subarctica (Gisin) , rather massive, with 3 teeth, lamellae absent ( Fig. 107 ). Ratio of manubrium: dens: mucro = 3.2–4.7: 1.4–2.2: 1. Lateral anal lobes each with two relatively long and one small chaetae, upper anal lobe with two small and one long chaetae.

Affinity. The new species is obviously closely related to S. subarctica (Gisin) . Both species are separated from other members of the genus by some unique characters (simple maxillary palp, 3 prelabral chaetae, reduced number of guards on labial papilla E), and their generic position may be changed in future. The two species differ in chaetotaxy of dens (6 anterior, 7–8 posterior in subarctica , 1 anterior, 3–4 posterior in indigirka ) and in the number of laterodistal chaetae on VT (3+ 3 in subarctica , 4+ 4 in indigirka ). S. indigirka has the largest manubrium: dens ratio (2.3 in average) of all Scutisotoma species studied here and generally the furca of the new species is rather similar to that of Weberacantha and Narynia.

Distribution. Known only from the type-locality in Yakutia.

Name derivation. The new species is named after the type-locality.

Figures

FIGURES 139–142. Scutisotoma indigirka sp.n. 139, posterior view of furca; 140, dens, lateral; 141; lateral sensillum and microsensillum on Abd.III (p-chaetae connected); 142, chaetotaxy of Abd.V (s: sensillum, ms: microsensillum).

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).