Scutisotoma millimetrica, 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 : 31-33

Scutisotoma millimetrica sp.n.

Figs. 80–86

Material. Holotype: ♀, Russia, southern part of Khabarovsk Territory, Badzhalsky Mt.

Range, on tree trunks, date unknown, leg. N. Babushkin. Paratypes: 14 exx., same locality, leg. N. Babushkin ( MSPU) .

Description. Size 0.5–0.9 mm. Colour of live specimens unknown (only rather old slides have been seen), but probably quite pale apart from the dark eye spots. Cuticle with fine primary granulation. Ocelli 8+8, G and H slightly smaller. PAO narrow elliptical, not constricted, about 2.0–2.5 as long as ocellus diameter and 0.9–1.2 as long as U 3. Maxillary outer lobe with bifurcate palp and 4 sublobal hairs. 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 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 6 distal s (AO and two lateral s, one of them slightly longer). Lateral guards and inner pair of sensilla in AO of slightly different size ( Fig. 85 ). Ant.2–3 with some additional sensilla in males, slightly shorter than ordinary chaetae. Sensilla on Ant.4 hardly differentiated, subapical organite small.

Dorsal axial chaetom of Th.II–Abd.III as 7–8,5/4,5,5–6. Thorax without ventral axial chaetae. Macrochaetae differentiated only 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 about half as long as ordinary chaetae. Sensillar formula 33/22224 (s) and 11/111 (ms) ( Fig. 80 ). Sensilla on Abd.I–III in mid-tergal position (medial sensillum on Abd.III set in posterior 1/3 of the tergite). Sensilla on Abd.V subequal and set in a line ( Fig. 86 ).

Unguis simple, without inner tooth. Ti.1–3 with 21-21-25 chaetae, as in the basic set. Sometimes there are 1–2 additional chaetae in proximal part of Ti.3. B-row on Ti.1–2 with 7 chaetae. Chaetae x and B 5 on Ti. 3 in males only slightly slender than ordinary chaetae. Tibiotarsal tenent chaetae (1-2-2) on Ti.1–3 clearly clavate, about as long as unguis (U 3: t.ch. = 0.9–1.3: 1). Ventral tube with 4+4 latero-distal chaetae and usually with 6 posterior ones. Tenaculum with 4+4 teeth and one chaeta. Anterior furcal subcoxa with 10–16 chaetae, posterior one with 6–7 chaetae. Anterior side of manubrium with a pair of distal chaetae, its posterior side with 11–13+11–13 on the main part and with 3–4 chaetae on each laterobasal lobe ( Fig. 81 ). Dens usually with 7 (6–8) anterior chaetae (proximal 1/ 3–1/2 of dens without chaetae, Figs. 82, 84 ). Posterior side of dens crenulated, usually with 7 chaetae (4 basal, 3 subapical, Fig. 83 ). Mucro with two teeth, subapical strongest. Ratio of manubrium: dens: mucro = 4.2–5.0: 3.0–3.9:1. Each anal lobe with 3 minute chaetae of similar length.

Affinity. Among the known East-Palaearctic species S. millimetrica is most similar to S. ananevae (Babenko & Bulavintsev) . Besides smaller size and different number of teeth on tenaculum, millimetrica differs in having relatively longer tergal sensilla (in S. ananevae they are much shorter compared with ordinary chaetae).

The same number of chaetae on dens is also shared with the two Spanish species fungi Selga and najtae Selga. Their generic position is not fully clear, but they most probably belong to the genus Proisotoma . Formally, they differ from S. millimetrica by having a different arrangement of chaetae on anterior side of dens and by having more laterodistal chaetae on VT.

Distribution. Known from several localities of the Badzhalsky Mt. Range (Far East of Russia).

Name derivation. The name reflects the small body size.

Figures

FIGURES 80–86. Scutisotoma millimetrica sp.n. 80, general distribution of sensillary elements; 81, genital field and manubrium, posterior view; 82–84, dens, anterior (82), posterior (83) and lateral (84); 85, Ant.3, dorsal; 86, chaetotaxy of Abd.V (s: accp-sensillum).