Scutisotoma Bagnall, 1949

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 : 15-16

Scutisotoma Bagnall, 1949

Type species: Proisotoma titusi Folsom

Syn.: Dimorphotoma Grinbergs, 1975: 101 (type species Dimorphiella muriphila Grinbergs, 1968: 139 ), syn.n.

Dimorphiella Grinbergs, 1968: 139

Diagnosis. Anurophorinae with all abdominal segments clearly separated. Furca in various stages of reduction. Manubrium with a pair of distal chaetae on anterior side, rarely without chaetae. Tergal sensilla on abdomen in mid-tergal position. All microsensilla present (11/111). B-row on Ti.1–2 complete.

Colour usually dark. Ocelli 5 to 8 on each side of head, PAO elliptical and rather wide. Integument with fine but visible primary granulation, sometimes clearly modified on last abdominal segments. Ant.1–3 with full set of bms. Maxillary palp usually bifurcate with 4 sublobal hairs. Labial papilla E with a full set of guards, rarely e 7 absent. Labral chaetotaxy 4/554. Sensilla (s) of Th.II-Abd.5 usually 33/22224, rarely 44/33334 ( armeriae ) or with increased number of sensilla ( titusi ). Thorax usually without ventral chaetae. VT with 4+4 or more laterodistal chaetae and usually more than two posterior chaetae. Tibiotarsal tenent chaetae (A 1 on Ti.1, A 1 and A 7 on Ti.2–3) clearly differentiated, clavate or truncate. Chaetae x and B 5 on Ti. 3 in males may be modified. Unguis simple, without tooth. Anterior chaetae on dens only in distal part. Mucro with 2–3 teeth, often lamellate, rarely completely absent.

Discussion. It should be mentioned that the type species, Proisotoma titusi Folsom , appears to differ from almost all other known species of the genus by an increased number of sensilla on tergites (see redescription below). This character may be common for Nearctic species, but Palaearctic species usually have 33/22224, with armeriae as the only exception (44/33334).

Because of a considerable variation in development of furca, our assemblage of Scutisotoma is not as homogenous as Proisotoma s.str. There are a number of species with partly reduced furca which are not treated by Potapov (2001) as Proisotoma , which obviously fit the above diagnosis (“ Subisotoma ” variabilis (Gisin) , “ Subisotoma ” stepposa (Martynova) , “ Stachanorema ” tolerans Babenko ).

A rather isolated position is taken by Scutisotoma subarctica (Gisin) comb.n. which has a simple maxillary palp, 6 guard chaetae on labial papilla E (e 7 absent), 3 prelabral chaetae and 3+3 lateral chaetae on VT. Also Scutisotoma fjellbergi (Dunger) comb.n. and Scutisotoma oirota (Vilkamaa) comb.n. differ from most other species of Scutisotoma by presence of ventral chaetae on Th.III and a simple maxillary palp.

Practically the same set of characters as in Scutisotoma is found in another group of species that are related to Weberacantha octa Christiansen (“ Proisotoma ” beckeri (Stebaeva) , “ Proisotoma ” janetscheki Yosii , and two new species described below). They differ from Scutisotoma only by a short furca with a massive mucro and by a long, narrow PAO. These characters link them to members of the Asiatic genus Narynia Martynova, 1967 which has an unclear generic status at present. Besides modified chaetae on tip of abdomen, the latter has no anterior chaetae on manubrium, which is not uncommon for Scutisotoma . Despite minor differences between Scutisotoma , Weberacantha, Narynia and Rhodanella we prefer to retain their generic status at present.

Known species of the genus. Scutisotoma armeriae (Fjellberg) comb.n., S. ananevae (Babenko & Bulavintsev) comb.n., S. christianseni (Stach) comb.n., S. fjellbergi (Dunger) comb.n., S. ladaki (Denis) comb.n., S. muriphila (Grinbergs) comb.n., S. oirota (Vilkamaa) comb.n., S. subarctica (Gisin) comb.n., S. stepposa (Martynova) comb.n., S. tianshanica (Martynova) comb.n., S. tolerans (Babenko) , comb.n., S. variabilis (Gisin) comb.n., and 14 new species described below.