Proisotoma dualis, Potapov, Mikhail & Bogomolov, Maxim, 2016

Potapov, Mikhail & Bogomolov, Maxim, 2016, Taxonomy of the Proisotoma complex. VI. Mobile forms of Proisotoma s. str. with the description of a new species from East Siberia (Collembola: Isotomidae), Zootaxa 4088 (2), pp. 257-267 : 257-260

Proisotoma dualis sp. nov.

Figs 1–9 , 12, 13 , 15 , 27, 28

Material. Holotype: unmodified adult female, Russia, East Siberia, Buryat Republic, Dzerginsky Nature Reserve, vicinities of Station 81 km (upper flow of Barguzin River), 1076 m alt., 55.349°N, 111.499°E, under bark of dead larch-tree, 10.ix.2012, leg. M. P. and A. Gulgenova. Paratypes. Nine specimens: sub-adult normal and mobile individuals from the same place. Type specimens deposited in MSPU.

Other material: Buryat Republic, nearby Goudjekit, valley of Akulikan Stream, ~ 900 m alt., Pinus sibirica forest, rotten debris under loose bark of fallen branches, 15.viii.2013, leg. M. P. and A. Gulgenova.

Description. Size 0.7–0.8 mm. Pigmentation weak, grey. Cuticle finely reticulated, size of largest polygons much smaller than bases of chaetae. Ocelli 8+8, G and H much smaller ( Fig. 7 ), size of ocelli effected by dimorphism, in normal specimens well recognized only by pigmentation, G and H hardly visible. PAO with 4 guard chaetae along posterior margin, elliptical, not constricted, as long as 0.6–0.8 of Ant. 1 width and 1.0–1.4 as long as U 3 ( Fig. 6, 7 ). Maxillary outer lobe with simple maxillary palp and 4 sublobal hairs. Labral formula as 3/ 554. Labium with all papillae (A – E), papillae A – D with normal number of guards (1,4,0,4), E with 5 guards. Main part of labium with 3 proximal and 4 basomedian chaetae. Ventral side of head with 4+4 postlabial chaetae. Ant.1 with 1 small basal ventral bms, 2 ventral s, and 12 chaetae, including one p -chaeta ( Fig. 5 ). Ant.2 with 3 bms and 1 laterodistal s not thicker than on Ant.1. Ant.3 without bms and with 6 distal s (including two lateral of which one long and one spine-like), guard s of AO long ( Fig. 5 ). S -chaetae on Ant.4 weakly differentiated, subapical organite small.

Body with smooth and rather short chaetae. Dorsal axial chaetom of Th.II–Abd.IV: 9–10,6–9/5–6,5–6,6,9–11. Th.I and II without ventral chaetae, Th.III with 1+1 (more rarely 1+2) ventral axial chaetae at ventral line. Abd.II without mid-ventral chaetae. Macrochaetae weakly differentiated, medial macrochaetae on Abd.V as long as 0.35– 0.55 of tergal midline ( Fig. 1 ). S -chaetae on tergites setaceous, vary in length (effected by dimorphism, Figs 27, 28 ). S -formula as 3,3/2,2,2,2,4 (s) and 0,0/0,0,0 (ms). S -chaetae on Abd.I–V in p -row of chaetae, on Th.II–III medial s just in front of p -row. On Abd.V s -chaetae arranged in one posterior row ( Fig. 1 ). Unguis simple, without inner or lateral teeth. Ti.1 and Ti.2 without additional chaetae (21), Ti.3 with 25–27 chaetae. B -row of chaetae on Ti.1–2 complete (B 4 and B 5 present). Modification of male spurs (x and B 5 on Ti.3) uncertain since fully adult males not seen by us. Tibiotarsal tenent chaetae short and pointed or long and clavate (2,2,2), effected by dimorphism, if clavate 1.6–2.0 as long as U 3 ( Figs 8, 9 ). Legs 1, 2, 3 with 1,1; 1,4; 4(5),5(6) chaetae on upper and lower subcoxa, respectively ( Fig. 1 ). Ventral tube with 4+4 distal and 4 posterior chaetae arranged in one transversal row. Tenaculum with 3+3 teeth and 3 chaetae. Anterior furcal subcoxae with 15–17 chaetae, posterior subcoxae with 6 chaetae. Anterior side of manubrium with a pair of distal chaetae ( Fig. 2 ), posterior side with 9– 10+9–10 chaetae on main part, lateral edges with one chaeta each ( Fig. 2 ), chaetotaxy of laterobasal lobes uncertain (at least with 4+4 chaetae). Dens rather short, effected by dimorphism: ratio dens: Ti.3 = 0.5–0.65 (normal form) or 0.65–0.75 (mobile form). Anterior side of dens with 6 chaetae arranged as 1,2,3, distal three in one transversal row ( Figs 2, 4 , 15 ) Posterior side of dens weakly crenulated or with humps and 4 chaetae, arranged as one chaeta at base, two at the middle and one distally ( Fig. 3 ). Mucro with 3 teeth as common for the genus. Ratio of manubrium: dens: mucro = 3.3–4.8: 2.0–3.1: 1.0. Males present.

Affinity. Proisotoma dualis sp. nov. is a typical member of Proisotoma Börner, 1901 sensu Potapov, Babenko & Fjellberg, 2006 by having s -chaetae on the abdomen in the p -row, reduced ms set, two guards lost in labial papilla E, simple palp of maxillary outer lobe and other characters. For the genus, so far only P. m i n ut a (Tullberg, 1871) and P. turikana Palacios-Vargas & Arbea, 2009 show a formula "0,0,1+1" for the ventral chaetotaxy of the thorax. Both species differ from P. dualis sp. nov. with the presence of ms on Th.II (ms formula 1,0/0,0,0 vs. 0,0/ 0,0,0), more chaetae on the posterior side of the dens (6 and 7, respectively, vs. 4), "4+4,1" formula of the tenaculum (vs. "3+3,3"), and the presence of a transverse row of mid-ventral chaetae on Abd.II (absent in P. dualis sp. nov.). Additional differences are the 4,4/3,3,3,3,4 s -formula and 5 ocelli in P. turikana and the presence of additional s -chaetae on Ant.3 in P. minuta . Apparently, by having two rare characters, 3+3 teeth on tenaculum and 0,0/0,0,0 ms -formula, the new species is closely related to P. minima . They differ in the number of ocelli (8+8 vs. 5+5), ventral chaetotaxy of Th.III (1+1 vs. 0+0), number of chaetae on tenaculum (3 vs. 1), and number of chaetae on posterior side of dens (4 vs. 5). The absence of ms- chaetae on all tergites of the body in P. dualis sp. nov. is unusual. Apart from P. m i n i m a, this peculiarity is probably shared with P. santosorum Palacios-Vargas & Arbea, 2009 described from a juvenile female collected in a cave in Venezuela. Missing of ms -chaetae in P. santosorum are assumed by us on the basis that they were neither figured nor mentioned in first description. Proisotoma santosorum more resembles P. minima since they share missing chaetae on Th.III, one chaeta on the tenaculum, and 5 posterior chaetae on the dens.

Distribution and ecology. Known from two localities in the Baikal region. It occurs only under loose bark of dead tree.

Name derivation. It is named after dimorphism.

Figures

FIGURES 1 – 9. Proisotoma dualis sp. nov.: 1, s - chaetae, macrochaetae and p - rows on body tergites; 2, posterior half of abdomen, lateral view in normal form; 3,4 furca in mobile form, posterior (3) and lateral view (4); 5, Ant. 1 – 3, lateral view; 6 – 7, ocelli and PAO in mobile (6) and normal (7) form; 8 – 9, distal part of Leg 2 in mobile (8) and normal (9) form.

FIGURES 10 – 13. Proisotoma minima (10, 11) and P. dualis sp. nov. (12, 13): 10, 12, normal forms; 11, 13, mobile forms.

FIGURES 15 – 16. Furcal complex of mobile forms of Proisotoma dualis sp. nov. (15) and P. minima (16).

FIGURES 23 – 29. Morphology of Proisotoma spp: normal (23, 25) and mobile forms (24, 26) of P. dottrensi (Moscow); 23 – 24, furca; 25 – 26, ocelli and PAO; 27, 28, P. dualis sp. nov., posterior row of chaetae in mobile (27) and normal (28) forms; 29, P. brevidens, dens in mobile form.