Tetracanthella tardoki, Potapov, Mikhail, Brinev, Alexey & Sun, Xin, 2019

Potapov, Mikhail, Brinev, Alexey & Sun, Xin, 2019, Isotomidae of Japan and Asiatic part of Russia. II. The genus Tetracanthella of the Far East, ZooKeys 855, pp. 31-54 : 45-47

Tetracanthella tardoki sp. nov. Figs 4, 41, 42-45, 46, 55-56, 58

Type material.

Holotype: female, Russia, Far East, Khabarovsky Krai, Nanaisky district, ~40 km S road Khabarovsk-Sov.Gavan, Tardoki-Yani Mt., ~2050 m alt., tundra on top, 16-26.06.2017, leg. A.B. 19 paratypes from the same place and nearby, 1800-1900 m alt.

Other material

(all from Tardoki-Yani Mt.): different open sites nearby type locality (moss and lichen on talus, mountain tundra, and mosses on rocks), 16-26.06.2017, leg. A.B.

Diagnosis.

Coxa I without an external chaeta. Macrochaetotaxy: 3(W),3(W)/2,3,3. Retinaculum and furca absent.

Description.

Body length 1.2-1.7 mm. Body slender, continuously narrowing (Fig. 41). Coloration dark, including antennae. Polygons large, canals between polygons well-marked. Smooth fields present on Abd. II–IV (Fig. 56), often on Abd.I. Head (Fig. 55), Th.II and III sometimes with narrow smooth belts at posterior edge. Area between ASi sometimes with small field. Dorsal mesochaetae rather short, slightly shortened in axial part of tergites (Fig. 43), in posterior row of Abd. IV not longer than on other parts of body (Md: p1 = 5.7-7.8). Abd. IV with p3 much longer than p1 (p3: p1 = 3.4-4.5). Macrochaetae long and thick.

8+8 ocelli, G and H reduced. PAO 2.5-3.3 as long as the diameter of ocellus A. Chaeta s’ of ant.III in males present. Two prelabral chaetae. Outer maxillary lobe with three sublobal hairs and simple maxillary palp. Labium with three proximal and four basomedian chaetae, labial palp with reduced set of guards [A(1)B(3)C(0)D(3)E(4)] (Fig. 4): papillae B and D each lost one dorsal guard (b4 and d4, respectively), papilla E lost three guards (e7 and probably e5 and e3). Postlabial chaetae 3+3. With 4-5 (rarely three in smaller and juvenile individuals) chaetae between medial line and pc3 on head. Frontal chaeta ap absent.

Chaetotaxy scarce (Figs 42, 43). Axial chaetotaxy 10,8/4,4,4,4. Macrochaetotaxy: 3(W),3(W)/2,3,3. Mdl macrochaetae in p-row on Th. II and III. Number of s-chaetae: 3,3 /2,2,2,2,4 (s), 1,0/1,0,0 (ms) (Fig. 46). S-chaetae short, medial ones on Abd. I–III arranged behind Mdl macrochaetae. Sternite of Th. III without chaeta.

Coxa I without an external chaeta. Tibiotarsi with 1,2,2 long and clavate dorsal tenent hairs and 3,3,1 enlarged ventral tenent hair (Fig. 45). Males with chaeta B5 and X on tibiotarsi III stick-like, thickened. Tibiotarsi I and II with 21 chaetae each, III with 22 chaetae. Claw without teeth. Empodial appendage very short, 0.15-0.20 as long as inner edge of claw (Fig. 45).

Ventral tube with 3+3 lateral and four posterior chaetae.

Retinaculum and furca absent. Retinacular field with 3-5 chaetae. Anterior furcal subcoxa with three (rarely two or four) chaetae, posterior one with four chaetae. Manubrial field normally with eight chaetae (Fig. 44). Anal spines parallel, large, on high papillae. Papillae of inner pair sclerotised. Medial mesochaetae (a1) of Abd. V anterior to medial macrochaetae (a2) (Fig. 43). Arrangement of chaetae and spines on dorsum of Abd V as a2-a2/a1-a1 = 1.6-1.8; a2-a2/a2-eAS = 1.5-2.0 (Fig. 43). Males present.

Etymology.

The species is named after the type locality.

Distribution and ecology.

It is known only from the Tardoki-Yany mountain massive (central part of Sikhote-Alin Range) where it occurs in all samples from alpine sites which we have examined (Fig. 58).

Discussion.

The new species belongs to the ' ethelae ' group by absence of chaeta on coxa I, three sublobal hairs, two prelabral chaetae and other characters. Together with T. orientalis they are the only representatives of this Nearctic group in Palearctic. The two species share several apomorphic characteristics unknown in North American species: absence of furca, presence of the third macrochaetae in p-position on thorax, low number of axial chaetae, short empodium. Tetracanthella tardoki sp. nov. differs from T. orientalis by the presence of Md macrochaetae on Abd.II resulting in formula 2,3,3 (vs. 2,2,3) on abdomen.