Folsomia breviseta Potapov & Kuznetsova

Potapov, Mikhail, Hasegawa, Motohiro, Kuznetsova, Natalia, Babenko, Anatoly & Kuprin, Alexander, 2018, Isotomidae of Japan and the Asiatic part of Russia. I. Folsomia ' inoculata' group, ZooKeys 750, pp. 1-40 : 5-6

Folsomia breviseta Potapov & Kuznetsova sp. n. Figs 11, 12, 14, 15-20

Type material.

Holotype, female, Russia, NE Yakutia, Middle Indigirka, near Ust-Nera, 700 m alt., larch forest with thick lichen cover, litter, 22.vii.1992. Ten paratypes from the same biotope, five paratypes from mountain tundra (1500 m alt.) with bushes of Betula nana and one paratype from mosses in stony niche on northern slope (1600 m alt.) in the same location. All collected by N. Kuznetsova and M. Potapov. Deposited in MSPU.

Diagnosis.

Blind. Dorsal macrosetae (Md) present on both Th.II and Th.III. Sensillary formula complete (43/22235; 10/100). Medial s-setae on body tergites short, set in anterior position. Macrosetae short. Ventral setae on Th.III absent. Anterior side of manubrium normally with 2+2 setae, dens with 18-22 anterior setae. Mucro bidentate.

Description.

Body size from 1.0 (one adult male) to 1.7 mm. Body shape relatively tubular, general appearance not typical of ' inoculata ' group due to short macrosetae (Fig. 12). Without ocelli and pigmentation. Cuticle with fine, hexagonal primary granulation ( “smooth”). PAO slender and long, middle constriction varies, 'inner denticles’ usually well developed, PAO length 1.8-1.9 as long as width of Ant.I and 2.3-2.5 as long as inner unguis length (Fig. 14). Labium complete, guard setae e7 present, three proximal and four basomedian setae. Ventral side of head with 4+4 postlabial setae. Ant.I with 13-15 common setae, two ventral s-setae (s) and three basal micro s-setae (bms): two dorsal bms (short and long) and one ventral bms. Ant.II with three bms and one latero-distal s, Ant.III with one bms and four distal s (lateral s absent, Fig. 15). Several tubular s-setae on Ant.IV. Organite small.

Common setae short. Sensillary formula as 43/22235 (s) and 10/100 (ms). S-setae short, four s-setae on dorsal side of Abd.V longer. Medial s-setae on Th. II–Abd.III situated in front position, on Abd. I–III between Md and Mdl (Figs 16, 17). Abd.V with five s-setae arranged as three in dorsal position, thin, as long as common setae (as, accp1, accp2), one lateral, thicker than dorsal, and one latero-ventral, short ( ‘3+1+1’ pattern) (Fig. 18), accp3 s-setae subequal to accp2. Macrosetae smooth and short, 2,2/3,3,3 in number, medial ones on Abd.V much shorter than dens (2.3-3.1) and 1.8-2.3 times longer than mucro (Fig. 18). Axial chaetotaxy as 10 –12,7–8,/5– 6,5,5. Thorax without ventral setae.

Empodial appendage as long as 0.5-0.6 unguis. Tibiotarsi with 24-27 setae on legs I–II, and 28-32 on leg III. Upper and lower subcoxae of legs I–III with 0,1/3,6 –8/5–7,7– 9 setae, respectively. Coxae of leg I with two front setae. Ventral tube with 4+4 latero-distal and 5-7 posterior setae (two in distal transversal row and 3-5 in more proximal position), anteriorly without setae. Tenaculum with 4+4 teeth and a seta. Anterior furcal subcoxae with 12-15, posterior one with six setae. Anterior side of manubrium normally with 2+2 setae at distal edge, arranged in two longitudinal lines (Fig. 19). One additional seta often present on one side in a distance from main group resulting in 2+3 set (Fig. 11). One of the paratypes shows 2+1 anterior setae on manubrium (Fig. 20). Posterior side of manubrium with 4+4 latero-basal, two apical setae (ap), 2+2 setae in distal transversal row (M1, L1), two pairs of lateral setae, and 5 –6+5– 6 in central part (Fig. 11). Dens with 18-22 anterior setae. Posterior side of dens crenulated and with seven setae: four basal, two at the middle, and one (not especially small) at base of mucro (Fig. 11). Mucro bidentate. Ratio of manubrium: dens: mucro = 4.1-4.5: 5.1-5.8: 1. Males present.

Remarks.

Folsomia breviseta sp. n. combines several characters rare for the group: short macrosetae and s-setae, anterior position of medial s-setae on body tergites, the absence of ventral setae on Th.III. A loss of lateral s-setae on Ant.III is a very peculiar character while the nature of this character is not easy to interpret since all species of the family Isotomidae , if not all Collembola , have these s-setae. The absence of s-setae was confirmed in all available specimens. Beyond ' inoculata ' group several blind species with two pairs of setae on manubrium can be confused with F. breviseta sp. n., for example, F. bisetosa Gisin, F. cephalota Bu et al., and F. sensibilis Kseneman. All these species belong to other groups and therefore differ essentially by characters of high rank.

Distribution and ecology.

The species is known only from the type locality where it inhabits mountain forests and tundra.

Derivatio nominis.

The new species name reflects short setae on body.