Hydroporus acutangulus Thomson 1856

Hydroporus acutangulus Thomson, 1856

The species was described by Thomson (1856: 202) after specimens from northern Sweden, "Lappland" (very roughly estimated to 67N 26E; circle (1) in Fig. 13). The type localities of the five other known synonyms are also given as circles in Fig. 13: (2) Hydroporus punctatulus J. Sahlberg, 1889 (Russia, Kola peninsula, Chavanga; 66.113N 37.777E); (3) H. sumakovi (Russia, Novaya Zemlya, Belushya Guba; 71.535N 52.327E) (circle with question mark, see notes below); (4) H. pectoralis (Russia, Siberia, Neuleva river, Spirino; 61.167N 69.814E); Hydroporus zaitzevi Jacobson, 1908 is a replacement name for H. pectoralis and, thus, has the same type locality as the latter; (5) H. aenescens (Russia, Siberia, Yenisei, Bryokhovsky Island, ca. 70.83N 83.00E, and Nikandrovsky Island, ca. 70.67N 83.00E). For more details about the taxa mentioned above see Nilsson (2001) and the comprehensive discussion in Falkenström (1929: 151). We have studied several specimens from Sweden, Finland, northern Norway and Russia (Republic of Karelia) (MNB, CHF). In addition we have studied the male from the Russian Far East, Primorsky krai, Ussuriysky Rayon, Kaimanovka, ca. 43.63N 132.24E (CLH; circle 6 in Fig. 13) which has been cited in Pederzani (2001: 236). Hydroporus acutangulus is almost entirely black or has the elytra very dark brownish (Fig. 1); all specimens studied appear at least darker than those H. polaris which are at our disposal. The males have the elytra shiny and not reticulate behind the base; however, in the posterior part of the first third, traces of reticulation can be found: not complete meshes, but short indistinct lines between the punctures. More distally, this reticulation becomes more prominent, and near the apex it is replaced by small complete meshes. In the northern European males studied the pronotum is reticulated with small meshes, except a small area on disc. In the male from the Russian Far East this smooth area is extended more to the sides and reaches until the base. Females often have distinct reticulation on large parts of the upper surface (Nilsson & Holmen 1995: 48), but are, nevertheless, shiny. Further comparative notes can be found below under H. polaris. The species can be easily distinguished from H. sejilashan sp. n. by the arcuate anterior protarsal claws (males) and the shiny surface.