Abstract
A subterranean species of pseudocrangonyctid amphipod, Pseudocrangonyx gudariensis Tomikawa & Sato, sp. n., is described from the spring-fed stream Gudari-numa in Hakkoda Mountains, Aomori Prefecture, northern Japan. Pseudocrangonyx gudariensis is morphologically similar to P. coreanus Uéno, 1966 and P. febras Sidorov, 2009 based on its relatively small body size, small number of articles of rami of pleopods, and urosomite 1 without basal setae. However, P. gudariensis is distinguished from those species based on the following characteristics: from P. coreanus, antenna 2 of female without calceoli, palmar margins of gnathopods 1 and 2 with distally notched robust setae, inner margin of inner ramus of uropod 2 with 4 robust setae, and basal part of inner ramus of uropod 2 without slender seta; and from P. febras, carpus of gnathopod 2 without serrate robust setae on posterodistal corners, peduncle of pleopods 1 and 2 with setae, and longer article 2 of uropod 3. Phylogenetic analyses using nuclear 28S rRNA and histone H3, and mitochondrial cytochrome c oxidase subunit I and 16S rRNA markers showed that P. gudariensis is placed among known Pseudocrangonyx Akatsuka and Komai, 1922 species. However, its exact phylogenetic position within the genus could not be determined. The polyphyly of the Japanese Pseudocrangonyx species indicates that multiple colonization events of Pseudocrangonyx ancestors to the Japanese Archipelago could have occurred. The reliability of the past Pseudocrangonyx records from Japan is briefly discussed.
Highlights
P. gudariensis is distinguished from those species based on the following characteristics: from P. coreanus, antenna 2 of female without calceoli, palmar margins of gnathopods 1 and 2 with distally notched robust setae, inner margin of inner ramus of uropod 2 with 4 robust setae, and basal part of inner ramus of uropod 2 without slender seta; and from P. febras, carpus of gnathopod 2 without serrate robust setae on posterodistal corners, peduncle of pleopods 1 and 2 with setae, and longer article 2 of uropod 3
Phylogenetic analyses using nuclear 28S rRNA and histone H3, and mitochondrial cytochrome c oxidase subunit I and 16S rRNA markers showed that P. gudariensis is placed among known Pseudocrangonyx Akatsuka and Komai, 1922 species
The first species, P. shikokunis, which was subsequently designated as the type species by Barnard and Barnard (1983) by position precedence, was reported from Tokushima Prefecture in Shikoku, and Hyogo, Okayama, and Yamaguchi Prefectures in the western area of Honshu, Japan (Akatsuka and Komai 1922, Uéno 1927, 1933a, c, Tomikawa et al 2008); P. yezonis was collected in Hokkaido and Akita Prefecture in the northern area of Honshu (Akatsuka and Komai 1922, Uéno 1933b, Matsuda 1954); and P. kyotonis has been recorded from Kyoto, Gifu, Shizuoka, and Shimane Prefectures in Honshu (Akatsuka and Komai 1922, Uéno 1927, 1971a, c, Nunomura 1975)
Summary
Amphipods that belong to the genus Pseudocrangonyx Akatsuka & Komai, 1922 inhabit subterranean waters of Japan, the Korean Peninsula, eastern China, and the Far East of Russia; this genus currently includes 20 species (Sidorov and Gontcharov 2013).Pseudocrangonyx was originally established for the three Japanese subterranean species (Akatsuka and Komai 1922): P. shikokunis Akatsuka & Komai, 1922; P. yezonis Akatsuka & Komai, 1922; and P. kyotonis Akatsuka & Komai, 1922. The first species, P. shikokunis, which was subsequently designated as the type species by Barnard and Barnard (1983) by position precedence, was reported from Tokushima Prefecture in Shikoku, and Hyogo, Okayama, and Yamaguchi Prefectures in the western area of Honshu, Japan (Akatsuka and Komai 1922, Uéno 1927, 1933a, c, Tomikawa et al 2008); P. yezonis was collected in Hokkaido and Akita Prefecture in the northern area of Honshu (Akatsuka and Komai 1922, Uéno 1933b, Matsuda 1954); and P. kyotonis has been recorded from Kyoto, Gifu, Shizuoka, and Shimane Prefectures in Honshu (Akatsuka and Komai 1922, Uéno 1927, 1971a, c, Nunomura 1975). It is highly possible that there are many undescribed species in the Japanese Archipelago
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