Opisa is a small amphipod genus including three species: O. eschrichtii (Krøyer, 1842) from the North Atlantic Ocean (Sars 1895; Bousfield 1987), Arctic (Bousfield and western Pacific (Stebbing 1906; Derzhavin 1929); odontochela Bousfield, 1987 southeast Alaska 1987); tridentata Hurley, 1963 coasts of America 1987). During field survey marine benthic fauna Hokkaido, Japan, one authors (KK) collected an undescribed species off Akkeshi Bay using sledge net. This paper describes illustrates new...

A new species of the maerid amphipod, Elasmopus nkjaf, from Miyako Island, Ryukyu Islands, Japan, is named and described. Additionally, nucleotide sequences nuclear 28S ribosomal RNA histone H3 as well mitochondrial cytochrome c oxidase subunit I 16S its holotype paratype were determined. nkjaf sp. nov. belongs to rapax-group, distinguished other rapax-group by long setae on ventral margin epimeral plate 3, gland cone peduncular article 2 antenna not reaching end propodus gnathopod 1...

A new subterranean species of pseudocrangonyctid amphipod, Pseudocrangonyx joolaei, is described from the groundwater a cave in South Korea. joolaei sp. nov. can be distinguished its congeners by number sternal gills as well combination antennal sinus, accessory flagellum antenna 1, and terminal article uropod 3. Molecular phylogenetic analyses based on nuclear 28S rRNA histone H3, mitochondrial cytochrome c oxidase subunit I 16S genes revealed that P. formed clade with akatsukai Tomikawa...

A new species of the eusirid amphipod, Rhachotropis reiwa is described from off Amamioshima Island, northwestern Pacific. The differs its congeners in having large eyes, middorsal tooth on pereonite 7, pleonite 3 and urosomite 1 without dorsolateral teeth, basis pereopod 5 strongly produced posteriorly, 6 with triangular basis. key to Japanese adjacent waters provided. Additionally, a nucleotide sequence mitochondrial cytochrome c oxidase subunit I holotype was determined for future study.

Two new species of Maera Leach, 1814 and Quadrimaera Krapp-Schickel & Ruffo, 2000 included in the Maera-clade are described from Japan. denticoxa sp. nov. was collected Iwate Hokkaido Prefectures can be distinguished its congeners by small notches on posteroventral margins coxae 1–6. angulata north Tanegashima Island Kagoshima Prefecture is characterized distal tooth mandibular palp article 1, rounded palm female gnathopod 2, angular posterodistal margin pereopod 7 basis. Keys to...

Two missing syntypes of the Japanese subterranean amphipod Procrangonyx japonicus (Uéno, 1930), type species Schellenberg, 1934, were rediscovered in collections Kyoto University Museum. The morphology uropod 3, which has been considered principal diagnostic character genus, is redescribed on basis one syntypes, and nomenclatural history generic names Eocrangonyx 1937 (corrected from 1936) for some Far-Eastern reviewed. Owing to confusion between terms “type fixation” designation”—the latter...

Sternomoera moneronensis Labay, 1997, a poorly known freshwater amphipod, is redescribed based on newly collected specimens from its type locality, Moneron Island in the northern Sea of Japan. Certain inaccuracies original description, viz., shape antennal sinus head and number sternal gills ventral margin pereonite 7, are corrected.

A new species of sebid amphipod, Seba marianaensis sp. nov., is described from the Shinkai Seep Field, Mariana Trench, at a depth 5689–5683 m. nov. most similar to bathybia; however, it differs S. bathybia by setation mandibular palp and uropod 3 ramus shape gnathopod 1 coxa. This first record Sebidae Trench.

Luciobliviidae, a new family in the superfamily Gammaroidea (Amphipoda: Crustacea), is described on basis of species genus Lucioblivio gen. nov. from subterranean waters Japan. Mesogammaridae Bousfield, 1977 rediagnosed; Octopupilla Japan and Eoniphargus (Uéno, 1955) Korea included. The members Lucioblivio, share several characters, including reduced eyes, setose body, coxae, feeble appendages pedunculate coxal gills. To elucidate phylogeny three genera among others, sequence analysis 28S...

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. morphologically similar to P. coreanus Uéno, 1966 and febras Sidorov, 2009 based on its relatively small body size, number articles rami pleopods, urosomite 1 without basal setae. However, distinguished those following characteristics: coreanus, antenna 2 female calceoli,...

A new species of amphipod, Sternomoera morinoi Tomikawa and Ishimaru, is described from subterranean aquatic habitats in Shiga Prefecture, Japan. In addition, Relictomoera tsushimana (Uéno, 1971) a well on the island Tsushima Japan transferred to redescribed based holotype. sp. nov. most similar S. comb, nov., but distinguished by having many fine setae body, shorter antenna 1, fewer C-setae mandibular palp article 3, sparsely setose anterior margins coxae 1–4, different armature palmar...

In recent years, the impact of rising water temperatures associated with global warming on cold-water freshwater organisms has become a major issue, and understanding physiological ecological elements that support temperature limits is essential for conservation biology organisms. We describe new species thermophilic hyalellid amphipod, Hyalella yashmara sp. nov. from Peruvian hot spring Baños del Inca Cajamarca this could potentially contribute to high preference these. found can live in...

Abyssododecas styx, a new genus and species of Phtisicidae (Amphipoda), is described based on specimens collected from cold-seep sites at abyssal depths between 5313 |$7322\;{\rm{m}}$| in the Japan Trench, North Pacific, using crewed submersible Shinkai 6500 Remotely-Operated Vehicle Kaiko. This deepest yet record caprellidean amphipod. While A. styx n. gen., sp. looks like member Caprellidae, this can be assigned to through possession normally articulated pereopod 3 lack molar mandible. The...

The genus Jesogammarus contains 16 species in two subgenera, and Annanogammarus. To examine relationships among the genus, a molecular phylogenetic study including eight of former subgenus four latter was conducted using partial DNA sequences mitochondrial COI 12S rRNA genes. MP, NJ, ML trees based on combined data indicated monophyly Annanogammarus, though left unresolved. Consistent with few morphological differences, (A.) naritai J. suwaensis showed low genetic differentiation did not...

Amphipods belonging to the crangonyctoid genus Pseudocrangonyx Akatsuka & Komai, 1922 constitute a major component of subterranean environments in east Asia. The true species diversity this group has been unsettled due lack molecular data for P. shikokunis and kyotonis taxonomic status misidentified populations these two species. is herein clarified. Morphological comparisons among specimens name-bearing types demonstrate are distinctive Phylogenetic analyses using partial sequences nuclear...

Gammarus koreanus Ueno, 1940, which was originally described from the Korean Peninsula, is recorded fresh-waters of Goto Islands, Japan. This first record its occurrence in Molecular analyses using partial sequences 28S rRNA gene strongly support identity Japanese populations with G. koreanus. The specimens differ original description this species following features: antenna 2 lacking calceoli, inner margins and outer rami uropod 3 plumose setae, margin ramus without setae. These differences...

A new subterranean species of pseudocrangonyctid amphipod, Pseudocrangonyx daejeonensis sp. n. is described from the interstitial waters in Daejeon, Korea. distinguished three morphologically similar congeners, P. coreanus Uéno, 1966, febras Sidorov, 2009, and gudariensis Tomikawa & Sato, 2016, by characteristics antenna 1, 2, mandible, gnathopod pleopods, uropods 1–2, telson. Molecular phylogenetic analyses based on nuclear 28S rRNA histone H3, mitochondrial cytochrome c oxidase subunit I...

A new species of anisogammarid amphipod, Jesogammarus (Jesogammarus) ikiensissp. n., is described from freshwaters in the Iki Island, Nagasaki Prefecture, Japan, based on results morphological and molecular analyses. The distinguished all members genus by combination small number setae dorsal margins pleonites 1–3, short posterior peduncular articles antennae, mandibular article 1 without setae, well developed lobes accessory coxal gills gnathopod 2 pereopods 3–5, pectinate palmar margin...

Two new species of anisogammaris amphipod, Jesogammarus (Jesogammarus) bousfieldi and J. (J.) uchiyamaryui, are described from mountain streams in Yamagata Prefecture brackish waters on Iki Fukue Islands, Nagasaki Prefecture, Japan. is morphologically almost similar to paucisetulosus Morino, 1984. However, distinguished by the more number marginal setae pleonites. uchiyamaryui resembles ikiensis Tomikawa, 2015, but former differs latter two posterior margin peduncular article 2 antenna 1,...

To assess the taxonomic relationship between G. nipponensis and sobaegensis, morphological features molecular phylogenetic relationships using nuclear 28S rRNA mitochondrial COI genes were examined. Detailed observations revealed that sobaegensis clearly distinguishable. In addition to differences, these two species genetically diverged. course of this study, an undescribed was found from Tsushima Iki Islands described here as mukudai. analyses, monophyletic nipponensis, mukudai shown but...