Scutisotoma stachanoremi, 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 : 47-49

Scutisotoma stachanoremi sp.n.

Figs. 127–133

Type material. Holotype: ♀, Alaska, Nome , wet moss with Equisetum , 01.ix.1976, leg. R. Greenberg. Paratypes: 1 ex., same sample. 3 exx., Alaska, Cape Krusenstern , dry sandy beach ridge with moss, lichen, grass, Artemisia sp. , 03.ix.1976, leg. R. Greenberg. Stored in ONC (holotype and 2 paratypes) and MSPU (2 paratypes) .

Description. Size 0.7–0.8 mm. Colour background yellow-brown, tergites and ocular spots with diffuse dark pigment, ventral side and extremities paler. Cuticle with fine but visible granulation. Ocelli 5+5, subequal ( Fig. 129 ). PAO elliptical, narrow and without constriction, as long as U 3. Maxillary outer lobe with 4 sublobal hairs and bifurcate maxillary palp. 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 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 + one lateral s). Guards of AO clearly longer than inner pair of sensilla. In the single observed male additional sensilla on Ant.2–3 were not seen. Sensilla on Ant.4 hardly differentiated, subapical organite small.

Dorsal axial chaetom of Th.II–Abd.III as 6–7,5–6/3–4,3–4,3–4. Thorax without ventral axial chaetae. Macrochaetae differentiated laterally on Th.II–III and on tip of abdomen. Medial macrochaetae on Abd.V are 0.3–0.4 as long as tergite. Sensilla on tergites rather long (about 1/2 of length of ordinary chaetae). Sensillary formula 33/22224 (s) and 11/111 (ms). On Th.II–III one sensillum of the lateral group always set in a posterior position ( Fig. 131 ). Sensilla on Abd.I–III in mid-tergal position (medial sensillum on Abd.III slightly behind middle of the tergite). Microsensillum on Abd.II–III set close to the lateral sensillum ( Figs. 130 ). One of the medial sensilla (accp 2) on Abd.V is in anterior position ( Fig. 132 ).

Unguis simple, without inner tooth. Ti.1–3 with 21-21-23(24) chaetae. B-row on Ti.1–2 with 7 chaetae. Chaetae x and B 5 on Ti.3 hardly different from ordinary chaetae (only one male seen). Tibiotarsal tenent chaetae (1-2-2) pointed or slightly clavate, clearly shorter than unguis (U 3: t.ch. = 1.1–1.3:1). Ventral tube with 4+4 latero-distal and 6–7 posterior chaetae. Tenaculum with 3+3 teeth and a chaeta. Anterior furcal subcoxa with 5–8 chaetae, posterior with 3–4 ( Fig. 93 ). Furca short, hardly exceeding posterior margin of Abd.III. Anterior side of manubrium without chaetae, posterior side with only 7–10+7–10 chaetae including those on the laterobasal lobes. Dens short and plump, with 3(2) posterior chaetae, anterior side without chaetae ( Fig. 127 ). Mucro short but clearly separated from dens, usually hook-like (two paratypes have an additional tooth on one of the mucro) ( Fig. 128 ). Ratio of manubrium: dens: mucro = 9.2–13.3: 4.0–6.7: 1.

Affinity. S. stachanoremi sp.n. is easily identified by the 5+5 ocelli, strongly reduced furca without anterior chaetae on manubrium and dens, and a hook-like mucro.

The new species seems to be rather similar to the European alpine species S. variabilis (Gisin) the generic position of which was discussed by Fjellberg (1993). The latter is distinguished by a minute but stable character, the presence of one subapical anterior chaeta on dens.

Among Nearctic members of the complex our new species is probably most related to Scutisotoma tolerans (Babenko) , which differs by having a full set of ocelli (8+8), 2+2 tenacular teeth and no mucro. “ Stachanorema ” contra Christiansen & Bellinger also has a furca very similar to our new species, but differs by having 2+2 ocelli and more chaetae on tenaculum. The generic affinity of contra should be re-examined. Also the status of Stachanorema should be re-evaluated by studies of its type species, S. arnaudi Wray.

Distribution. Known from two sites of western Alaska.

Name derivation. The species is probably related to members of the genus Stachanorema .

Figures

FIGURES 127–132. Scutisotoma stachanoremi sp.n. 127, posterior view of furca and female genital plate; 128, dens, lateral (right: mucro in other specimen); 129, PAO and ocelli; 130, lateral sensillum and microsensillum on Abd.II–III (p-chaetae connected); 131, chaetotaxy of lateral part of Th.II (p-chaetae connected, s: sensillum, ms: microsensillum); 132, chaetotaxy of Abd.V (s1–4: accp1–4 sensilla).

FIGURES 133–138. Scutisotoma baica sp.n. 133, posterior view of furca and female genital field; 134, dens, anterior; 135, dens, lateral; 136, tibiotarsus 1; 137, tibiotarsus 3; 138, chaetotaxy of Abd.V (s: accp-sensillum).

FIGURES 93–98. Scutisotoma schisti sp.n. 93, subapical microsensillum and organite on Ant.4 (Taimyr); 94, ditto (Tuva); 95, tip of leg 3 in male (Taimyr, B5, x: modified chaetae in male); 96, ditto (Tuva); 97, preanal chaetae (Taimyr); 98, ditto (Tuva).