Tetracanthella manschurica Kutyreva, 1980

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 : 40-41

Tetracanthella manschurica Kutyreva, 1980 Figs 7, 23-25, 26-35, 53, 58

Material

(all from the Far East of Russia): Khabarovski Krai, Imeni Lazo district, upper flux of Katen River, Ko Mt., upper part of Ko Stream, ~970 м alt., 29.06.2018, soil in coniferous forest, A.B.; Khabarovski Krai, Vaninski district, ~14 km N Vysokogorny, upper flux of Mulinka River, closed spruce forest at pass, ~900 m alt., 29.09.2011, leg. M.P.; Primorski Krai, Partyzanski district, Olkhovaya Mt., 1380 m alt., 43.3375°N, 133.6615°E, spruce litter, 20.08.2018, leg. M.P., A.K.; Primorski Krai, Chuguevski district, Oblachnaya Mt., 1230 m alt., 43.6483°N, 134.1978°E, spruce litter, 19-20.09.2018, leg. A.K.; Primorski Krai, Chuguevski district (unprecise locality), spruce forest, 8.09.1973, leg. L. Kutyreva.

Description based on the aforementioned specimens.

Body length 1.6-1.9 mm. Body thick, tubular, not narrowed (Fig. 7). Coloration dark blue, distal half of antennae white. Reticulation very thin, polygons much smaller than mesochaeta socket (Fig. 53). No smooth fields. Size of dorsal mesochaetae variable (see the Remarks part), not shortened in axial part of tergites (Md: p1 = 1.3-1,5). Abd. IV with p3 subequal to p1. Macrochaetae acuminate.

8+8 ocelli, G and H smaller. PAO short, 1.1-1.6 as long as the diameter of ocellus A (Fig. 28). Chaeta s’ of Ant.III in males absent. Four prelabral chaetae. Outer maxillary lobe with four sublobal hairs and simple maxillary palp. Labium with complete set of guards [A(1)B(4)C(0)D(4)E(7)], three proximal and four basomedian chaetae. Postlabial chaetae 4 –5+4– 5. With 8-10 chaetae between medial line and pc3 on head. Frontal chaeta ap present.

Chaetotaxy abundant (Figs 23, 24). Axial chaetotaxy often asymmetrical 12 –14,8/8,8,8,8– 10 Macrochaetotaxy: 3(W),3(W)/2,2,2 (Fig. 27). Mdl macrochaetae in p-row on Th. II and III. Number of s-chaetae: 3,3/2,2,2,2,4 (s), 1,1/1,1,1 (ms) (Fig. 27). S-chaetae short, medial ones on Abd. I–III arranged lateral to Mdl macrochaetae. Sternite of Th. III without chaetae.

Coxa I without an external chaeta. Tibiotarsi with 1,2,2 long and clavate dorsal tenent hairs and without well developed ventral tenent hairs. Tibiotarsi with many additional chaetae on all legs, tibiotarsi I and II with 26-28 chaetae each, III with more than 30 chaetae (Fig. 34). Empodial appendage 0.7-0.8 as long as inner edge of claw, with apical filament.

Ventral tube with 3+3 laterodistal and four posterior chaetae. Retinaculum with 4+4 teeth and a chaeta. Anterior furcal subcoxa with 10-17 chaetae, posterior one with 3-4 chaetae (Fig. 33). Posterior side of manubrium with 6(7)+6(7) chaetae on main part and 3+3 on basolateral parts (9+9 at whole) (Figs 26, 32). Mucro indistinctly bidentate, with two teeth and some lamellae which make illusion of tridentate or quadridentate mucro (Figs 26, 29-32, 35). Anterior side of dens with three anterior chaetae, one larger and in more distal position and two (rarely one) smaller on both its sides. Posterior side with six (rarely five) chaetae, arranged as 1+1+(1)+2+1 (Figs 29-31). Dens:claw III = 3.1-4.8 (see the Remarks part). Manubrium: dens: mucro = 6.8-9.3: 4.6-7.1: 1. Inner and outer anal spines parallel, relatively small, on unsclerotised high papillae. Medial mesochaetae (a1) of Abd. V at level or slightly posterior to medial macrochaetae (a2) (Figs 24, 25). Arrangement of chaetae and spines on dorsum of Abd V as a2-a2/a1-a1 ~3.0; a2-a2/a2-eAS ~1.7. Males present.

Distribution and ecology.

Tetracanthella manschurica occurs in the mountains of Sikhote-Alin Range (Fig. 58). It is a rare species preferring coniferous litter.

Discussion.

Tetracanthella manschurica was described from Lazovski district of Primorski Krai. Afterwards, it was recorded once with few morphological remarks by Potapov (2001). The only known type individual of the species is probably lost and our redescription is based on 15 specimens from three different districts of the same region. These specimens share several peculiar features and generally fit to the original description. Some discrepancy between the text of the first description and our observations is probably due to the juvenile condition of the holotype ( Kutyreva 1980). Tetracanthella manschurica belongs to the ' sylvatica ' group and differs from other species of the group ( T. sylvatica , T. annulata sp. nov., and T. dorsoduplex by three chaetae on anterior side of dens, absence of crenulation on posterior side of dens, thin reticulation of cuticle, dark blue colouration and few chaetae on posterior side of manubrium and posterior furcal subcoxa. Tettracanthella manschurica additionally has very peculiar mucro which appears to have three or four teeth due to one or two lamellae. Regardless the lamellae, mucro of this species keeps the general bidentate pattern known in the genus.

Population from the northern part of Sikhote-Alin Range (Vaninski district) show longer meso- and macrochaetae (Fig. 24), clearly clavate tenent hairs on legs, longer claws (dens:claw III = 3.1-3.6) and mucro (dens: mucro = 4.6-5.1: 1) (Figs 30, 31). More southern populations (Fig. 58) (correspond better to the type specimens morphology because of shorter meso- and macrochaetae (Fig. 25), slightly (vs. clearly) clavate tenent hairs, short claws (dens: claw III = 4.1-4.8) and short mucro (dens: mucro = 6.7-7.1: 1) (Fig. 29). We include both forms to the diagnosis of T. manschurica in view of the possible ecomorphic nature of the differences. One individual of unclear status from Kunashir Island (Alekhino, leg. I. Volonikhina) differs from continental populations by much shorter dens.