Porrhomma boreale

Porrhomma boreale (Banks, 1899)

Figs. 9A–F.

Gongylidium borealis Banks, 1899 — Banks (1899): p. 347, Pl. A, Fig. 1 (descr. ♂ ♀); transferred by Eskov (1988). Oedothorax borealis — Strand (1906): p. 445.

Porrhomma nunamo Holm, 1970 — Holm (1970): p. 194, Figs. 12–15 (descr. ♂ ♀); synonymised by Eskov (1988). P. kulczynskii Staręga, 1974 — Staręga (1974): p. 22, Figs. 7–8, Phot. 3 (descr. ♀); synonymised by Tanasevitch (2013a). P. borealis — Eskov (1988): p. 105; transfer, synonymy.

P. boreale — Tanasevitch (2013a): p. 184, Figs. 105–116 (♂ ♀); synonymy.

Material examined. RUSSIA: Sakhalin Isl., East Sakhalin Mt. Range, below Chamginski Pass, 50°41.951'N, 143°16.234'E, 528 m a.s.l., 8 Aug 2001, 1 ♀. Chukotka Autonomous Okrug, Christ Bay, env. of Egvekinot Town, 15–17 Jul 1988, 2 ♀. NE Siberia, Magadan Area, env. of Magadan, 1st Arman Pass, 59°39.5'N, 150°30.9'E, 700 m a.s.l., 30 Jun 2004, 1 ♀, leg. Yu. M. Marusik. Chita Area, Sokhondo Nature Reserve, mountain tundra, 16 Jul?, 1 Ƌ 2 ♀, leg. S. Danilov. Upper reaches of Kolyma River, Sibit-Tyellakh env., 20 Aug 1984, 3 Ƌ 1 ♀, leg. K. Yu. Eskov (CYM). Central Siberia, Evenk Autonomous Region, delta of Neptene River, 15 Jul 1982, 16 Ƌ 31 ♀, leg. K. Yu. Eskov. Norilsk City, 29 Aug 1983, 1 Ƌ.

Diagnosis. The AP has the form of a bird head (e.g. Fig. 9B) in three large species (CW> 0.70): P. boreale, P. convexum and P. nekolai. P. boreale can be distinguished from the later two species by relatively short legs, Mt I/ CW = 0.77–0.81; in P. convexum 0.91–1.06, in P. nekolai 1.31–1.47. Females of P. boreale can be easily recognised from all the other species of the genus Porrhomma by very long main sacks and appendices, which are coiled along main sacks (Figs. 9C–F).

Description. ♀ (from Taymyr Peninsula, Russia, 15 Jul 1982). Carapace yellow-brown, 0.80 mm wide, PME– PME = 1.3 (Fig. 9A). Abdomen greyish yellow. Fe I–II with one dorsal spine, Fe I with one prolateral spine. Ti I with one prolateral spine, Ti I–II with one retrolateral spine. Tm Mt I = 0.36, Mt I/CW = 0.81.

Epigynum with characteristic translucent picture of main sacks and appendices (Fig. 9C). Spermathecae start on ascending part of the copulatory ducts. Main sacks are broad and coiled in one thread of the helix; their tops are oriented obliquely towards the abdominal wall. Very long appendices are coiled along main sacks and oriented oblique towards the median plane (Figs. 9D–F).

Ƌ (together with female). Embolus of middle length, AP of the form of a bird head (Fig. 9B), similar to the embolic section of the P. pygmaeum.

Variation. Ƌ ♀. Carapace 0.80–0.87 mm wide. Tm Mt I = 0.31–0.39, Mt I/CW = 0.77–0.81 (n = 6).

Ecology. Occurs in boreal and mountainous habitats.

Comments. Eskov (1985: 126) noted: “Specimens from Aleutian Islands determined by Holm (1960) as P. convexum are probably P. boreale.” G. Giribet examined and photographed the material collected by Holm, which is deposited in the Museum of Comparative Zoology at Harvard University, Cambridge, Mass. Females from Kodiak Island and Unalaska Island are P. convexum, but the female from Attu Island is Porrhomma boreale. Attu is the westernmost and largest island in the Near Islands group of the Aleutian Islands, it is situated in the close neighbourhood to Commander Islands.

Global distribution. Polar Urals, Siberia, Mongolia, Russian Far East (Tanasevitch 2013a), Commander Islands (Banks, 1899), Sakhalin Island and Attu Island (Aleutian Islands) (this paper). See Fig. 10.