A New Species of the Genus Pseudocrangonyx (Crustacea: Amphipoda: Pseudocrangonyctidae) from Yonaguni Island, Southwestern Japan, and Historical Biogeographic Insights of Pseudocrangonyctids.

The subterranean amphipod genus Pseudocrangonyx is diverse in Far East Asia, including the Japanese Archipelago. However, Pseudocrangonyx species have not been recorded from the Ryukyu Islands, which extend southwest of the Japanese Archipelago. This study describes a new species of Pseudocrangonyx, Pseudocrangonyx dunan sp. nov., from Yonaguni Island, Ryukyu Islands, Japan. Phylogenetic analyses revealed that P. dunan sp. nov. is a sister species to Pseudocrangonyx sp. 4 from Honshu Island, Japan. In addition, three monophyletic groups were found in Pseudocrangonyx, although the phylogenetic positions of several species remain unknown. Our divergence dating indicates that the differentiation of major lineages of Pseudocrangonyx, which contains species from both the Asian continent and the Japanese Archipelago, is concentrated around 20 MYA. These results suggest that the opening of the Sea of Japan is one of the major factors promoting the speciation of Pseudocrangonyx endemic to the archipelago.

A new species of the genus Podocerus from the Seto Inland Sea, Japan (Crustacea, Amphipoda, Podoceridae).

A new podocerid amphipod, Podocerussetouchiensis sp. nov., is described from the Etajima Island, the Seto Inland Sea, Japan. This new species differs from its congeners by the dorsal carination of pereonites and pleonites, and form of the antenna 1, gnathopods 1 and 2, uropods 1 and 2, and telson. Nucleotide sequence data of the mitochondrial cytochrome c subunit I (COI) from a paratype of Podocerussetouchiensis sp. nov. is provided for future molecular systematic studies.

On the brink of extinction: a new freshwater amphipod Jesogammarusacalceolus (Anisogammaridae) from Japan.

Freshwater habitats, especially cold springs, are environments in which the risk of extinction faced by organisms remains high due to human activities. To conserve endangered species, it is important to describe and name them. Here, a new, endangered freshwater anisogammarid amphipod species, Jesogammarus (Jesogammarus) acalceolussp. nov., found in a spring in Aomori Prefecture, Japan, is described which is potentially the sole remaining habitat of this species. Both morphological and molecular phylogenetic results strongly support the nesting of the new species within Jesogammarus. Jesogammarus (J.) acalceolussp. nov. is the first species of genus Jesogammarus that was found to lack a calceolus, a sensory organ located on male antenna 2. Thus, the diagnostic criteria for this genus required amendment. A reconstruction of ancestral calceoli, based on a molecular phylogenetic tree, revealed that the common ancestor of Jesogammarus possessed calceoli, which were secondarily lost in J. (J.) acalceolussp. nov. Our results indicate that this new species, which is key to clarifying the evolution of the calceolus, is of high conservation significance.

A new species of Princaxelia from Shinkai Seep Field, Mariana Trench (Crustacea, Amphipoda, Pardaliscidae).

A new pardaliscid amphipod, Princaxelia marianaensis sp. nov., is described from a single female captured at the Shinkai Seep Field, Mariana Trench, from a depth of 5,689-5,683 m. A key to species of Princaxelia is provided. This is the first species of Princaxelia to be described from the Mariana Trench, and the second report of this genus from this region.

Molecular phylogenetic position of Minamitalitrus zoltani elucidates a further troglobisation pattern in cave-dwelling terrestrial amphipods (Crustacea: Talitridae).

Talitrids are a highly diverse group of amphipod crustaceans that have colonized various terrestrial habitats. Three genera have successfully adapted to cave habitats on islands in the Pacific and Atlantic Oceans. However, the evolutionary origin of the Pacific troglobitic talitrids has remained unknown. We estimate the phylogenetic position of the troglobitic Minamitalitrus zoltani, which inhabits limestone caves on Minamidaito Island in the Northwestern Pacific, on the basis of the traditional multi-locus dataset. For the analyzed talitrids, we also reconstruct ancestral states of the maxilliped palp and male gnathopod 2. Our results indicate that Minamitalitrus zoltani is sister to the epigean Nipponorchestia curvatus with a deep divergence. Nipponorchestia curvatus inhabits coastal habitats in Japan, but is not indigenous to Minamidaito Island. A previous study estimated that the Atlantic troglobitic species had invaded subterranean habitats multiple times, but we provide new insight into the troglobisation history in talitrids. We also recover secondary shifts of character states of the maxilliped palp and male gnathopod 2 within the lineage composed of Minamitalitrus and its phylogenetically close genera. Our findings highlight the need for the genus-level reclassification of these genera; we split Nipponorchestia into two genera, establishing a new genus for Nipponorchestia nudiramus.

A new species of Nicippe from the Bering Sea (Crustacea, Amphipoda, Pardaliscidae), with a redescription of N. tumida.

A new pardaliscid amphipod, Nicippe beringensis, is described from the Bering Sea at depths between 520 and 536 m, and N. tumida Bruzelius, 1859 is redescribed based on specimens from Fredrikshald, Norway, near the species' type locality. Nucleotide sequences of mitochondrial cytochrome c oxidase subunit I (COI) from the holotype and a paratype of N. beringensis sp. nov. are reported. While N. beringensis sp. nov. is similar to N. tumida, it differs from the latter in having an asetose palp article 1 of maxilla 1, a gnathopod 1 coxa with a straight distal edge, and in the posterior margin of the basis of gnathopods 1 and 2, and pereopod 3, being heavily setose in females. A key to species of Nicippe is provided.

A new cave amphipod, Pseudocrangonyx wonkimi sp. nov. (Crustacea, Amphipoda, Pseudocrangonyctidae), from the Korean Peninsula.

A new species of pseudocrangonyctid amphipod, Pseudocrangonyx wonkimi sp. nov., was found in the groundwater of a cave in the southwestern Korean Peninsula. Pseudocrangonyx wonkimi sp. nov. is morphologically most closely related to P. joolaeiLee et al., 2020. However, P. wonkimi is clearly distinguished from P. joolaei by lacking sternal gills, fewer setae on maxilla 1 inner plate, fewer serrate robust setae on the carpus of the gnathopods, lacking bifid setae on the inner ramus of pleopod 3, and fewer articles of rami on pleopod 3. We also determined sequences of mitochondrial cytochrome c oxidase subunit I (COI) of P. wonkimi sp. nov. for molecular diagnosis. From the molecular analysis based on COI sequences, P. wonkimi showed the closest relationship with P. joolaei with 15.1% genetic distance.

The complete mitochondrial genome of Jesogammarus (Jesogammarus) hinumensis (Crustacea: Amphipoda: Anisogammaridae).

We determined the mitogenome sequence of Jesogammarus (Jesogammarus) hinumensis Morino, 1993, which is the first complete mitogenome sequence in the family Anisogammaridae Bousfield, 1977. The complete mitogenome of J. (J.) hinumensis was 15,186 bp in length with the typical 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs), and a control region (CR). The gene order of J. (J.) hinumensis was in accordance with the typical pan-crustacean ground pattern. A maximum-likelihood tree constructed using 25 eumalacostracan mitogenomes confirmed that J. (J.) hinumensis is most closely related to the family Micruropodidae, and supported the monophyly of the superfamily Gammaroidea.

Complete mitochondrial genome of Pseudocrangonyx joolaei (Crustacea: Amphipoda: Pseudocrangonyctidae).

The complete mitochondrial genome of a subterranean pseudocrangonyctid amphipod, Pseudocrangonyx joolaei, was determined in this paper. The complete mitogenome of P. joolaei was 14,814 bp in length with the typical 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs, and a control region (CR). The gene order of P. joolaei was unique in that the CR was an inversion, and the gene order of Pseudocrangonyx was not concordant when compared to that of P. daejeonensis, a subterranean amphipod found in Korea. A maximum-likelihood tree, constructed based on 26 eumalacostracan mitogenomes, confirmed that P. joolaei supported monophyly in the family Pseudocrangonyctidae and is most closely related to the superfamily Crangonyctoidea.

A new species of the genus Elasmopus from Miyako Island, Japan (Crustacea: Amphipoda: Maeridae).

A new species of the maerid amphipod, Elasmopus nkjaf, from Miyako Island, Ryukyu Islands, Japan, is named and described. Additionally, nucleotide sequences of nuclear 28S ribosomal RNA and histone H3 as well as mitochondrial cytochrome c oxidase subunit I and 16S ribosomal RNA from its holotype and paratype were determined. Elasmopus nkjaf sp. nov. belongs to the rapax-group, and distinguished from the other rapax-group species by long setae on ventral margin of epimeral plate 3, gland cone of peduncular article 2 of antenna 2 not reaching to end of peduncular article 3, propodus of gnathopod 1 facially setose, length of propodus of male gnathopod 2 shorter than 3 times as long as length of carpus, medial face of propodus of male gnathopod 2 shallowly hollowed, posterior margin of epimeral plate 3 without denticles. A key to the species of Elasmopus species occurring Japanese and adjacent waters is provided.

Reassessment of the Groundwater Amphipod Paramoera relicta Synonymizes the Genus Relictomoera with Paramoera (Crustacea: Amphipoda: Pontogeneiidae).

The systematic status of the stygobitic amphipod, Paramoera relicta Uéno, 1971, was revisited based on morphological examination of the paratypes, and molecular phylogenetic analyses using a newly collected specimen from its type locality. The paratypes clearly showed that this species does not possess the "sinusoid" antennal sinus in the head, which was erroneously described in the original description of this species; P. relicta is unquestionably classified within the genus Paramoera Miers, 1875 . Molecular phylogenetic trees obtained with nuclear histone H3 and mitochondrial 16S rRNA demonstrated that P. relicta clearly belongs to the clade consisting of Paramoera species. Since the genus Relictomoera Barnard and Karaman, 1982 was erected according to the "sinusoid" characteristic of its type species P. relicta, this genus is no longer valid, and should be treated as a junior subjective synonym of Paramoera. One of the paratypes of P. relicta is herein designated as a neotype for the species to clarify its taxonomic status and emend the morphological characteristics of this pontogeneiid amphipod.

A new species of Melita from Japan (Crustacea, Amphipoda, Melitidae).

A new brackish-water species of melitid amphipod, Melita choshigawaensis, from the Choshigawa River, Mie Prefecture, Japan, is named and described. Melita choshigawaensissp. n. is distinguished from the most similar M. shimizui (Uéno, 1940) by having an elongate and weakly arched male uropod 3, and a deep and strongly hooked anterior lobe of the coxa on the female's pereopod 6. Nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I (COI) of M. choshigawaensis and M. shimizui support divergence at the species level. A key to the Japanese species of Melita is provided.

A new species of the genus Pseudocrangonyx (Crustacea, Amphipoda, Pseudocrangonyctidae) from Korea.

A new subterranean species of pseudocrangonyctid amphipod, Pseudocrangonyx daejeonensissp. n. is described from the interstitial waters in Daejeon, Korea. Pseudocrangonyx daejeonensissp. n. is distinguished from three morphologically similar congeners, P. coreanus Uéno, 1966, P. febras Sidorov, 2009, and P. gudariensis Tomikawa & Sato, 2016, by the characteristics of antenna 1, antenna 2, mandible, gnathopod 2, pleopods, uropods 1-2, and telson. Molecular phylogenetic analyses based on nuclear 28S rRNA and histone H3, and mitochondrial cytochrome c oxidase subunit I and 16S rRNA genes revealed that P. daejeonensis is a sister species of the unnamed Pseudocrangonyx sp. 3 inhabiting central Japan.

The complete mitochondrial genome of Pseudocrangonyx daejeonensis (Crustacea: Amphipoda: Pseudocrangonyctidae).

The complete mitogenome sequence of a subterranean pseudocrangonyctid amphipod, Pseudocrangonyx daejeonensis, was determined. The complete mitogenome of P. daejeonensis was 15,069 bp in length with the typical 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), 2 ribosomal RNAs (rRNAs), and a control region (CR). This is the first complete mitogenome sequence in the family Pseudocrangonyctidae. Interestingly, gene arrangements of most amphipod species were almost identical to the typical pan-crustacean ground pattern, whereas two PCGs, both of rRNAs and CR were translocated in P. daejeonensis. A maximum-likelihood tree, constructed based on 30 eumalacostracan mitogenomes, confirmed that P. daejeonensis is closely related to the crangonyctid Stygobromus indentatus and S. tenuis potomacus and supported the monophyly of the superfamily Crangonyctoidea.

Molecular Phylogeny and Surface Morphology of Thiriotia hyperdolphinae n. sp. and Cephaloidophora oradareae n. sp. (Gregarinasina, Apicomplexa) Isolated from a Deep Sea Oradarea sp. (Amphipoda) in the West Pacific.

In an effort to broaden our understanding of the biodiversity and distribution of gregarines infecting crustaceans, this study describes two new species of gregarines, Thiriotia hyperdolphinae n. sp. and Cephaloidophora oradareae n. sp., parasitizing a deep sea amphipod (Oradarea sp.). Amphipods were collected using the ROV Hyper-Dolphin at a depth of 855 m while on a cruise in Sagami Bay, Japan. Gregarine trophozoites and gamonts were isolated from the gut of the amphipod and studied with light and scanning electron microscopy, and phylogenetic analysis of 18S rDNA. Thiriotia hyperdolphinae n. sp. was distinguished from existing species based on morphology, phylogenetic position, as well as host niche and geographic locality. Cephaloidophora oradareae n. sp. distinguished itself from existing Cephaloidophora, based on a difference in host (Oradarea sp.), geographic location, and to a certain extent morphology. We established this latter new species with the understanding that a more comprehensive examination of diversity at the molecular level is necessary within Cephaloidophora. Results from the 18S rDNA molecular phylogeny showed that T. hyperdolphinae n. sp. was positioned within a clade consisting of Thiriotia spp., while C. oradareae n. sp. grouped within the Cephaloidophoridae. Still, supplemental genetic information from gregarines infecting crustaceans will be needed to better understand relationships within this group of apicomplexans.

Rediscovered syntypes of Procrangonyx japonicus, with nomenclatural consideration of some crangonyctoidean subterranean amphipods (Crustacea: Amphipoda: Allocrangonyctidae, Niphargidae, Pseudocrangonyctidae).

Two missing syntypes of the Japanese subterranean amphipod Procrangonyx japonicus (Uéno, 1930), the type species of Procrangonyx Schellenberg, 1934, were rediscovered in the collections of the Kyoto University Museum. The morphology of uropod 3, which has been considered the principal diagnostic character of the genus, is redescribed on the basis of one of the syntypes, and the nomenclatural history of the generic names Procrangonyx and Eocrangonyx Schellenberg, 1937 (corrected from 1936) for some Far-Eastern subterranean amphipod species is reviewed. Owing to confusion between the terms "type fixation" and "type designation"-the latter being just one means of accomplishing the former-the view that Procrangonyx is unavailable and invalid has prevailed in recent literature. Procrangonyx was indeed proposed after 1930 with no type species "designation", but under Articles 67.2.1 and 68.3 of the International Code of Zoological Nomenclature, Eucrangonyx japonicus Uéno, 1930 was "fixed" as its type species by monotypy in the original publication. Since a diagnosis of the genus was also provided in the same work, Procrangonyx is available under Article 13.3 of the Code. However, because endopodal segmentation of uropod 3 proves to be variable in P. japonicus, doubt is thrown on the taxonomic distinctness of Procrangonyx vis à vis Pseudocrangonyx Akatsuka Komai, 1922. Additionally, the publication dates of Allocrangonyx Schellenberg, 1937 and Niphargus foreli speziae Schellenberg, 1937 are corrected from 1936.

A new species of the genus Nicippe from Japan (Crustacea, Amphipoda, Pardaliscidae).

A new species of the pardaliscid amphipod, Nicippe recticaudata, from off Cape Toi, Japan, is named and described. This is the first record of Nicippe Bruzelius, 1859 from the western Pacific coast of the Japanese archipelago. Additionally, nucleotide sequences of nuclear 28S ribosomal RNA and histone H3 as well as mitochondrial cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA from the holotype and paratypes were determined. The morphological characteristics and the COI distance values enforced the distinctiveness of N. recticaudatasp. n. among the known Nicippe species. Nicippe recticaudatasp. n. closely resembles N. tumida Bruzelius, 1859 in having a two-dentate posterior margin of usoromite 1. However, the former is distinguished from the latter by the posterior margin of merus of pereopod 4 with 5-6 setae, anterior margin of merus of pereopod 5 with 9-10 setae, and telson with straight inner margin, tapering proximally. A key to the species of Nicippe is provided.

Evaluation of the Systematic Status of Geographical Variations in Arcuphantes hibanus (Arachnida: Araneae: Linyphiidae), with Descriptions of Two New Species.

The systematic status of geographical variants of Arcuphantes hibanus Saito, 1992 belonging to the A. longiscapus species group, indigenous to western Honshu and Shikoku, Japan, was evaluated using morphological and molecular data. Two species, A. enmusubi Ihara, Nakano and Tomikawa, sp. nov. and A. occidentalis Ihara, Nakano and Tomikawa, sp. nov., are described, and A. hibanus is redescribed with redefinition of its taxonomic status. These three species are diagnosed by the characteristics of paracymbium, pseudolamella, and epigynal basal part. Phylogenetic trees obtained with mitochondrial cytochrome c oxidase subunit I and 16S rRNA markers showed that the variants are mutually genetically highly diverged. However, the mtDNA phylogenies failed to recover the monophyly of A. hibanus redefined herein. Contrary to the mtDNA phylogenetic analyses, a neighbor-network analysis of nuclear internal transcribed spacer 1 sequences of A. hibanus, A. enmusubi and A. occidentalis spiders showed that each of them forms a cluster. The results of mitochondrial and nuclear DNA analyses in each of the three species are briefly discussed, along with their taxonomic identities.

Praobdellidae (Hirudinida: Arhynchobdellida) is not specific only to the mucous-membrane after all: Discovery of a praobdellid leech feeding on the Japanese freshwater crab Geothelphusa dehaani.

Praobdellid leech species have been known to infest vertebrate mucous-membrane; some of them have been assumed to be invertebrate bloodsuckers. Praobdellid individuals were found feeding on the Japanese freshwater crab, Geothelphusa dehaani, at Mt. Tsukuba, Ibaraki Prefecture, Japan. The leech had inserted its head into the intersegmental membrane between the crab's carapace and legs. Our findings represent a first invertebrate host record for praobdellid leeches. Additionally, molecular phylogenetic trees based on nuclear 18S and 28S rRNA, mitochondrial cytochrome c oxidase subunit I, and 12S rRNA sequences as well as the leech morphological characteristics showed that the present leech might belong to an unrecognized praobdellid lineage: a taxonomic revision of the Japanese praobdellid species is needed.

A new species of the rare genus Priscomilitaris from the Seto Inland Sea, Japan (Crustacea, Amphipoda, Priscomilitaridae).

A new species of the priscomilitarid amphipod, Priscomilitaris heike, from the Seto Inland Sea, Japan, is named and described. This new species is the third species of Priscomilitaridae and the second species of Priscomilitaris. Additionally, nucleotide sequences of nuclear 28S rRNA and histone H3 as well as mitochondrial cytochrome c oxidase subunit I from its holotype were determined. Priscomilitaris heike sp. n. is distinguished from its congener, Priscomilitaris tenuis Hirayama, 1988, by having deep antennal sinus, long flagellar article 1 of antennae 1 and 2, long mandibular palp article 2, 10 robust setae on outer ramus of maxilla 1, and rounded epimeral plates. A key to the species of Proscomilitaridae is provided.