Folsomia heterothorax, Potapov, Mikhail & Gulgenova, Ayuna, 2013

Potapov, Mikhail & Gulgenova, Ayuna, 2013, Isotomidae (Collembola) of Buryat Republic. II. A revision of the genus Folsomia, Zootaxa 3682 (2), pp. 305-330 : 309-311

Folsomia heterothorax sp. nov.

Figs 2–8

Type material. Holotype: female. Russia (East Siberia), S Buryat Republic, Zagansky Range, eastern slope, 1074 m alt., 50.92895°N, 107.91876°E, pine wood with Rhododendron and Vaccinium vitis-idea on sandy soil, 21.viii.2011, leg. A.Gulgenova & L.Vanyavina. 6 paratypes, adult and subadult females from the same locality. Holotype and 3 paratypes in MSPU; 3 paratypes in BSU.

Other material. A specimen from E Buryatia, Kizhinginsky District, 2 km SE Innokent'evka, pine wood after fire, 07.vii.2012.

Description. Body size 0.9–1.0 mm. Lacking pigment on body. Body of typical habitus for the genus ( Fig. 2 ). Cuticle with thin, hexagonal, primary granulation ("smooth"). Ocelli lacking. PAO narrow and long, slightly constricted, 1.3–1.4 as long as width of Ant I and much longer than inner unguis length (1.6–2.0) ( Fig. 6 ). Maxillary outer lobe with 4 sublobal hairs, maxillary palp bifurcate. Labral formula as 4/5,5,4, chaetae of subapical row thick, chaetae of basal row thin, labral edge well developed. Labium with 5 papillae (А–Е), reduced set of guard chaetae (e7 absent), 3 proximal, 4 basomedian, and 5 basolateral chaetae. Ventral side of a head with 4+4 chaetae. Ant.I with 2 small basal microsensilla (bms), dorsal and ventral, and 2 ventral sensilla (s) ( Fig. 6 ), Ant.II with 3 bms and 1 latero-distal s, Ant.III with 1 bms and 1 lateral s, without additional sensilla. Sensilla on Ant.4 weakly differentiated. Organite pin-like, slightly swollen at the tip.

Sensillary formula as 4,3/2,2,2,3,5 (s), 1,0/1,0,0 (ms). Tergal sensilla thin, about as long as common chaetae and hardly distinguishable. Medial sensilla situated in posterior row of chaetae on Abd.I–III, and in front of this row on Th.II–III, on Abd.I–III between Mac1 and Mac2 ( Fig. 2 ). On Abd.IV three sensilla, two long and one shorter, grouped together, on dorsal side. Abd.V with 5 sensilla arranged with 3 dorsal ones (al, accp1, accp2) somewhat longer than 2 lateral sensilla, all sensilla subequally thin ( Fig. 3–4 ). Macrochaetae smooth and long, 1,2/ 3,3, 3 in number, medial ones on Abd.V 1.6–1.9 times shorter than dens and 5.8–6.6 times longer than mucro ( Fig. 4, 5 ). 7 strong foil chaetae at the tip of abdomen arranged in two transversal rows as 2+2 anterior (fa1 and fa2) and 1+2 posterior (fp0 and fp2), respectively. Axial chaetotaxy as 11–12,7–8/4–5,4–5,4–5. Thorax without ventral chaetae.

Unguis of normal shape, without lateral and inner teeth. Empodial appendage 0.50–0.55 as long as unguis. Tibiotarsi with many additional chaetae, more than 25 and 35 on Leg I and III, respectively. Tibiotarsal tenent chaetae pointed. VT with 4+4 laterodistal and 5–7 posterior chaetae, anteriorly without chaetae. Tenaculum with 4+4 teeth and 1 chaeta. Anterior furcal subcoxae with 12–15, posterior one with 5 chaetae. Anterior side of manubrium normally with 16 chaetae arranged as 6+ 6 in two groups and two pairs of smaller chaetae (1+1,1+1) in more proximal part ( Fig. 7 ). Posterior side of manubrium with at least 5+5 laterobasal, 2 apical chaetae (ap), 3+3 chaetae in distal transversal row (M1, ml1, L1), two pairs of lateral chaetae (l1,l2), and about 7+ 7 in central part (only two individuals were possible to observe). Dens with 26–29 anterior chaetae ( Figs 8 ). Posterior side of dens crenulated and with 6 chaetae (4 basal and 2 at the middle). Distal end of dens only with a weak dorsal indention, no minute chaeta ( Fig 8 ). Mucro bidentate. Ratio of manubrium:dens:mucro = 6–7:9–11:1.

Discussion. Two very rare characters make this species exceptional in the genus: dorsal position of all sensilla on Abd.IV and median macrochaetae present only on Th.III (macrochaetae formula on thorax "1,2"). In other species of the genus a pair of lateral sensilla of Abd.IV set on latero-ventral side and medial macrochaetae either present (2,2) or absent (1,1) on both Th.II and III (formula "1,2" is known only in few species of ' quadrioculata ' group). The group to which the species belongs to is not at all obvious. The posterior position of sensilla indicates either the ' fimetaria ' or ' inoculata ' group. Well developed "foils" chaetae and absence of ventral chaetae on Th.III are shared with the most species of the former group, while slender PAO and compact maxillary head are characteristic for the latter one. The decisive character discriminating the two groups is the number of macrochaetae on thoracic segments: 1,1 in ' fimetaria ' group vs. 2,2 in ' inoculata ' group. F. heterothorax sp. nov. is in intermediate position (1,2). In general appearance and foil chaetae the new species resembles F. culter Potapov & Chimitova, 2009 and F. maximovi sp. nov. The position of sensilla of this couple of species is very different. F. sparsosetosa (' fimetaria ' group) is most similar to the new species by sensillar equipment and morphology of the furca and foil chaetae. However, it does not show the two remarkable characters mentioned above (see also the key to species). F. heterothorax sp. nov. also shows the unusual combination of the absence of e7 guard chaeta on labial palp with the presence of bifurcate maxillary palp which is also shared with F. sparsosetosa .

Distribution and ecology. Known from two localities in southern and central parts of Buryatia ( Fig. 1 : loc. 3, 14).

Etymology. The species has different number of macrochaetae on Th.II and III that makes thoracic segmentation more heteronomic.

Figures

FIGURE 1. The sampling sites in Buryatia: 1 – 2 — Vitim Plateau (1 — Konda Basin, 2 — Eravna Basin), 3 – 5 — Selenga Low Plateau (3 — Zagansky Range, 4 — vicinities of Schuch'ye Lake, 5 — vicinities of Karasinoye Lake), 6 – 8 — Barguzinsky Range (6 — Ust' - Barguzin, 7 — vicinities of Barguzin, 8 — upper flow of Barguzin River), 9 — Khamar-Daban Range, 10 — Tunkinskiye Gol'tsy Range, 11 — vicinities of Ulan-Ude, 12 — estuary of Selenga River, 13 — vicinities of Khorinsk, 14 — vicinities of Unnokent'evka, 15 –– Turka.

FIGURES 2 – 6. F. heterothorax sp. nov.: 2, Habitus and chaetotaxy; 3 – 4, chaetotaxy of posterior part of Abd. IV, V and VI, dorsal (3) and lateral (4) views; 5, Th. II and III; 6, PAO and Ant. I.

FIGURES 7 – 10. F. heterothorax sp. nov. (7, 8) and F. f u m o s a sp. nov. (9, 10): 7, 9, Furca, anterior view; 8, dens; 10, anterior part of the head.