Revision of the alvinocaridid shrimp genus Rimicaris Williams & Rona, 1986 (Decapoda: Caridea) with description of a new species from the Mariana Arc hydrothermal vents.

A new species of alvinocaridid shrimp is reported, from the Northwest Eifuku hydrothermal vent field at 16191667 m depth on the Mariana Arc. A comprehensive phylogenetic reconstruction of Alvinocarididae based on the mitochondrial cytochrome c oxidase subunit I (COI) gene including this new species reveals the paraphyly of the genus Rimicaris Williams & Rona, 1986 with four other generaAlvinocaridinides, Manuscaris, Opaepele, and Shinkaicarisnested within it. We re-examine material of these four problematic genera, and synonymise them under Rimicaris whose diagnosis has been amended, in order to maintain a monophyletic Rimicaris. Our new species, Rimicaris cambonae sp. nov. is genetically close to Rimicaris loihi (Williams & Dobbs, 1995) comb. nov. (previously Opaepele loihi) with which it co-occurs, but can be morphologically distinguished by the less elevated dorsal surface of the rostrum, this being devoid of a median carina, a stronger pterygostomial tooth on the carapace, and a blunt rather than acuminate proximolateral process on the antennular stylocerite. Species previously assigned to the above listed, synonymized genera are also discussed, with new material examined for three key species: R. loihi, R. acuminata, and R. leurokolos. Further, Alvinocaridinides formosa Komai & Chan, 2010 and Manuscaris liui Wang & Sha, 2016 are synonymized under Rimicaris leurokolos (Kikuchi & Hashimoto, 2000) comb. nov. and R. acuminata (Komai & Tsuchida, 2015) comb. nov., respectively. Revised diagnoses are presented for R. loihi, R. acuminata, and R. leurokolos. After the present revision revision, Rimicaris now consists of 15 species.

Reappraisal of Eiconaxius farreae Ortmann, 1891 and Eiconaxius mortenseni Sakai, 1992 (Decapoda: Axiidea: Axiidae), with description of a new species from Japan.

The sponge associated axiid shrimp Eiconaxius farreae Ortmann, 1891 was originally described based on specimens from Sagami Bay, central Japan. Morphological examination of many specimens of Eiconaxius collected from Sagami Bay and nearby areas, and genetic data from the mitochondrial COI and 16S rRNA genes have revealed that three species are represented. This finding led to a reappraisal of the identity of E. farreae and E. mortenseni Sakai, 1992, also originally described from Sagami Bay. It has been clarified that two species (E. farreae and an undescribed species) were mixed in the syntype material of E. farreae, and consequently, a lectotype of E. farreae is designated in the interest of nomenclatural stability. Here, E. farreae and E. mortenseni are redescribed, and the third species is described as new, E. reconditus. The new species is morphologically very similar to E. mortenseni. Differentiating characters among closely allied species are reassessed. Previous records of E. farreae are reviewed in light of the present findings.

A new species of the mud shrimp genus Naushonia Kingsley, 1897 (Decapoda: Gebiidea: Laomediidae) from the Ryukyu Islands, southwestern Japan, inhabiting burrows of an axiidean shrimp.

A new species of the laomediid mud shrimp genus Naushonia Kingsley, 1897 is described and illustrated based on seven specimens collected from Okinawa Island, Ryukyu Islands, southwestern Japan. All specimens of Naushonia karashimai n. sp. were collected from burrows of a large axiidean shrimp, Neaxius acanthus (A. Milne-Edwards, 1879), which inhabits seagrass beds in inner reef lagoons. The new species is easily distinguished from all 16 known congeners by its tridentate rostrum and relatively narrow pereopod 1 palm with a proximally located pollex. Sequences of the mitochondrial 16S rRNA and COI genes were newly generated for five species and two species of Naushonia, including the new species, respectively. Preliminary phylogenetic analysis using sequences of the 16S rRNA gene was performed.

A new species of the alpheid shrimp genus Athanas Leach, 1814 (Decapoda: Caridea) from the Sea of Japan.

A new species of the alpheid shrimp genus Athanas Leach, 1814 is described based on a holotype from Wakasa Bay, Sea of Japan side of Honshu, Japan, at a depth of 90 m. Athanas exilis n. sp. appears close to A. sydnyensis Anker & Ahyong, 2007, but is distinguished from the latter by some morphological features, including the different shape of the telson, the shorter antennular stylocerite, more strongly produced distal lamella of the antennal scaphocerite, and less developed armature of the merus of the major cheliped. Preliminary genetic analysis using the mitochondrial 16S rRNA gene was performed to compare interspecific genetic divergence within the genus.

Squat lobsters of the superfamily Chirostyloidea (Decapoda: Anomura) from seamounts on the Nishi-Shichito and Mariana ridges, North-West Pacific off Japan, with descriptions of two new species.

A small collection of chirostyloid squat lobsters was studied, collected from seamounts on the Nishi-Shichito, West Mariana, and Central Mariana ridges, which have been collectively designated as marine protected areas (MPAs) of Japan. Specimens were collected using a remotely operated vehicle (ROV). Four species belonging to three families were identified, of which two are new to science: Uroptychus medius n. sp. (Chirostylidae), Eumunida smithii Henderson, 1885, E. treguieri de Saint Laurent & Poupin, 1996 (Eumunididae), and Sternostylus spiniger n. sp. (Sternostylidae). Identities of those species were assessed using an integrative approach based on morphological comparison and genetic analysis of two mitochondrial markers (COI and 16S rRNA genes). The two species of Eumunida represent the first records from Japanese waters.

Metabetaeus lapillicola, a new species of alpheid shrimp (Decapoda: Caridea) from Japan, inhabiting unusual pebble beaches.

The alpheid shrimp genus Metabetaeus Borradaile, 1899 was previously known from two species associated with anchialine pools and caves, M. minutus (Whitelegge, 1897) and M. lohena Banner & Banner, 1960, and one species inhabiting in coral reef, M. mcphersonae Anker, 2010. In this study, a new species of the genus is described based on fourteen specimens collected from Shizuoka and Mie Prefectures, Honshu, central Japan. Metabetaeus lapillicola n. sp. inhabits interstitial spaces among small pebbles deposited in lower intertidal to upper subtidal zone, representing rather unusual habitat not only for Metabetaeus, but even for carideans. It is distinguished from three congeneric species by the presence of a pterygostomial spine on the carapace, greatly unequal chelipeds with the major one being substantially elongate, and the lack of a distinct distolateral spine on the uropodal endopod. Phylogenetic analyses using the mitochondrial 16S rRNA and COI genes support the recognition of the new species. The generic diagnosis of Metabetaeus is emended to accommodate the new species.

A new deep-sea palaemonid shrimp assigned to Periclimenes Costa, 1844 (Decapoda: Caridea) from the West Mariana Ridge, northwestern Pacific.

A new palaemonid species, Periclimenes variabilis, is described and illustrated on the basis of four specimens from the Ritto Seamount, West Marina Ridge, northwestern Pacific, at depths of 642-666 m. Specimens of the new species were collected with an unidentified hexacoral of Primnoidae (Cnidaria), an antipatharian octocoral Leiopathes sp. (Cnidaria), and an unidentified crinoid (Echinodermata), suggesting association with those invertebrates. Morphological comparison and molecular phylogenetic analyses using the mitochondrial 16S ribosomal RNA and cytochrome C oxidase subunit I genes indicate that the new species is closest to Periclimenes uniunguiculatus Bruce, 1990 although the possession of more than two spiniform setae on either side of the telson in the new species is consistent with the generic diagnosis of Bathymenes Kou, Li & Bruce, 2016. In reference to the close relationship to the species currently assigned to Periclimenes Costa, 1844 and the unsettled taxonomy of the genus, the new species is provisionally assigned to Periclimenes. Differentiating characters between the new species and closely related taxa are discussed.

New record of two species of munidid squat lobster (Decapoda: Anomura) from the North-West Pacific off Japan.

Two species of munidid squat lobsters are newly reported from the North-West Pacific off Japan based on material collected by the recent cruise of R/V Kaimei (KM20-10C cruise) of the Japan Agency for Marine-Earth Science and Technology, exploring seamounts in the marine protected area (MPA): Gonionida kaimei n. sp. and Trapezionida psylla (Macpherson, 1994). Gonionida kaimei n. sp. closely resembles G. tangaroa (Ahyong, 2007) and G. rubrimana (Ahyong, 2007), but morphological characters and living colouration differentiate the new species from the latter two species. Genetic analysis using two molecular markers (mitochondrial COI and 16S rRNA genes) also supports the recognition of the new species. Trapezionida psylla has been recorded from the South-West Pacific, and thus the present material greatly extends the geographic range of the species to the North-West Pacific. The identity of the present specimens is also confirmed by the genetic data, as well as the morphological evidence. This study contributes to documenting the benthic invertebrate fauna of the Japanese MPA.

A new intertidal species of the thorid shrimp genus Heptacarpus Holmes, 1900 (Decapoda: Caridea) from Japan.

A new species of the thorid shrimp genus Heptacarpus Holmes, 1900, H. sadoi, is described and illustrated on the basis of six specimens from the southeastern coast of the Boso Peninsula, central Japan. All the specimens were collected from intertidal tide pools at low tide. Heptacarpus sadoi n. sp. belongs to the species group with epipods on the pereopods 13 and appears morphologically close to H. jordani (Rathbun, 1902) known from Japan and Korea. The new species is readily differentiated from H. jordani by the short rostrum with fewer dorsal teeth and the possession of only one spine on the distal margin of the basal article of the antennular peduncle. Genetic comparison using two mitochondrial markers (COI and 16S rRNA genes) also supports that the new taxon is distinct from H. jordani.

A new genus and new species of palaemonid shrimp (Decapoda: Caridea), associated with the deep-sea crinoid Metacrinus rotundus (Echinodermata: Isocrinidae), from Suruga Bay, Japan.

Metacrimenes fenestra, a new palaemonid genus and species is described on the basis of an ovigerous female and one juvenile specimen from Suruga Bay, central Japan. The specimens were associated with the stalked crinoid Metacrinus rotundus Carpenter, 1885, collected at a depth of 131200 m. Photographs taken in situ indicate that the shrimp lives ectosymbiotically on its crinoid host. The greatly reduced bud-like exopod on the third maxilliped links the new genus to Mesopontonia Bruce, 1967 (Indo-West Pacific) and Waldola Holthuis, 1951 (East Pacific), in which the exopod is absent, but the presence of antennal spine on the carapace and the non-elongate, symmetrical second pereopods immediately distinguish Metacrimenes n. gen. from these genera. Molecular phylogenetic analysis using a dataset concatenating two mitochondrial markers (16S rRNA and COI genes) clusters the new genus with Paraclimenes gorgonicola (Bruce, 1967), two species of Mesopontonia and Brucecaris tenuis (Bruce, 1969). However, in Paraclimenes Bruce, 1995 and Brucecaris Marin & Chan, 2006, the third maxilliped exopod is normally developed, flagellum-like. Other differentiating characters between the new taxon and the presumably allied taxa are discussed.

Clarification of the identity of deep-sea crab Tymolus uncifer (Ortmann, 1892) and validation of Tymolus melanommus (Doflein, 1904) (Decapoda: Brachyura: Cyclodorippidae).

Examination of material from Japanese waters has disclosed that two species have been confounded under Tymolus uncifer (Ortmann, 1892) (Decapoda: Brachyura: Cyclodorippidae) in previous literature. The identity of Tymolus uncifer sensu stricto is clarified in reference to the lectotype, and the second taxon is herein attributed to T. melanommus (Doflein, 1904), which was originally recognised as a forma of T. uncifer with one specimen from off Kenya and one specimen from Japan. A lectotype is herein selected for T. melanommus in the interest of nomenclatural stability. Differentiating characters between the two species are assessed in detail, and those two species are compared also with T. glaucommus (Alcock, 1894), T. similis (Grant, 1905), T. brucei Tavares, 1991, T. daviei Tavares, 1997, T. hirtipes Tan & Huang, 2000 and T. globosus Spiridonov & Trkay, 2007, all of them are considered as valid. Sexual dimorphism and ontogenetic variation are seen in the relative length and stoutness of the pereopods 2 and 3 in T. uncifer and T. melanommus, but the morphometric characters derived from the two pereopods are useful as diagnostic at comparison between same sex in adults. Comparison of partial fragments of the mitochondrial COI and 16S rRNA gene sequences strongly supports that the two taxa are distinct. Previous records of T. uncifer, including fossil records, are reviewed based on the present findings. Tymolus uncifer and T. melanommus are restricted to Japanese waters at present.

Three new species of the thorid shrimp genus Lebbeus White, 1847 (Decapoda: Caridea) from Nemuro Strait, Hokkaido, Japan, with supplemental note on L. fujimotoi Matsuzaki, Hibino amp; Komai, 2015.

Based on a collection of deep-water caridean shrimps captured by commercial baited traps and gill nets operated in Nemuro Strait, southwestern part of the Sea of Okhotsk, three new species of the thorid shrimp genus Lebbeus White, 1847, L. rufomaculosus n. sp., L. subtilis n. sp. and L. tenuipes n. sp., are described and illustrated. Integrative approach using morphological comparison and genetic analyses with the mitochondrial COI and 16S rRNA genes is taken to clarify specific identities of those newly recognized taxa. In addition, an aberrant male specimen of L. fujimotoi Matsuzaki, Hibino Komai, 2015 is reported, of which the identity is confirmed by genetic analyses.

New record of a rarely collected caridean shrimp Bathypalaemonella pandaloides (Rathbun, 1906) (Decapoda: Bathypalaemonellidae) from the West Mariana Ridge, northwestern Pacific.

The deep-sea caridean shrimp Bathypalaemonella pandaloides (Rathbun, 1906) (Bathypalaemonellidae) was heretofore known only from Hawaii (type locality) and French Polynesia. In this article, we report this rarely collected species on the basis of a single male specimen from the Ritto Seamount on the West Mariana Ridge, northwestern Pacific, at a depth of 657 m, collected by means of a remotely operated vehicle (ROV). The specimen is intact, enabling us to describe the characteristic major pereopod 2 of the species for the first time. The closest relative is B. zimmeri Balss, 1914, known only from the western Indian Ocean; fewer accessory spiniform setae on the pereopods 35 dactyli and the less produced distal lamella of the antennal scaphocerite distinguish B. pandaloides from B. zimmeri. K2P divergences of the mitochondrial COI and 16S rRNA genes in taxa attributed to Bathypalaemonella Balss, 1914 are presented. The present specimen was collected from an anthipatharian octocoral colony, Leiopathes sp. (Cnidaria), suggesting a commensal relationship.

Reinstatement of Hippolyte St. Pauli Brandt, 1851 as a valid species of Lebbeus White, 1847 (Decapoda: Caridea: Thoridae).

Comparison between materials from various localities in the North Pacific and North Atlantic, including specimens identified with Lebbeus polaris (Sabine, 1824) in previous studies, led the authors to reinstate Hippolyte St. Pauli Brandt, 1851 as a valid species of the thorid genus Lebbeus White, 1847 (Decapoda: Caridea), removed from the synonymy of L. polaris. Lebbeus sanctipauli is distinguished from L. polaris by the rostrum with fewer dorsal teeth in female and a better developed ventral blade in male, fewer dorsolateral spiniform setae on the telson (three or four, rarely five versus six to 12), the longer antennular stylocerite in females, stouter pereopods 35 with fewer accessory spiniform setae on pereopods 35 dactyli (three or four versus five to seven) and the possession of an epipod on the pereopod 3. Although L. polaris has been thought to have a circumpolar distribution, the occurrence of the species in the North Pacific Ocean needs to be verified.

A new species of the diogenid hermit crab genus Pseudopaguristes McLaughlin, 2002 from the Northern Mariana Islands, Micronesia.

The diogenid hermit crab genus Pseudopaguristes McLaughlin, 2002 is currently represented by 15 species worldwide. In this study, we describe a new species of the genus, P. flavioculus, based on a unique male holotype from off Sarigan, Northern Mariana Islands, Micronesia, at depth of 131133 m. The new species appears similar to the type species of the genus, P. janetkae McLaughlin, 2002, but the lack of conspicuous spines on the dorsal face of the right cheliped carpus, the possession of a median row of tiny spines on the dorsal face of the left cheliped carpus, and different colour pattern of the cephalic appendages and the ambulatory legs distinguish P. flavioculus n. sp. from P. janetkae. Pseudopaguristes has been differentiated from the two allied genera, Paguristes Dana, 1851 and Areopaguristes Rahayu, 2012, by the possession of eight functional pairs of gills (versus 13 pairs in Paguristes and 12 pairs in Areopaguristes), but our examination of the new species and three other congeneric species available for study clarifies that the development of arthrobranchs on the maxillipeds 3 and chelipeds is rather variable in species currently assigned to Pseudopaguristes. Careful observation of the anterior arthrobranchs is recommended to avoid misinterpretation in the counts of gill numbers.

A new species of the ghost shrimp genus Callianassa Leach, 1814 (Decapoda: Axiidea: Callianassidae) from Wakasa Bay, western Japan: the first representative of the genus from the Pacific region.

The ghost shrimp genus Callianassa Leach, 1814 is currently represented by six taxa, of which five are known from the eastern Atlantic and only C. persica Sakai, 2005 from the Persian Gulf. In this study, a new species of Callianassa is described and illustrated on the basis of material from the subtidal soft sediments (at 2628 m depth) in Wakasa Bay, western Japanese coast of the Sea of Japan. Callianassa ogurai n. sp. is the first species of the genus from the Pacific region. This study discusses characters differentiating the new species and other five congeneric species. Molecular phylogenetic analysis using the mitochondrial 16S rRNA gene supports the close relationship between the new species and C. subterranea (Montagu, 1808), warranting the generic assignment of the new species to Callianassa sensu stricto. We also explore the contentious taxonomic status of C. timiris (Sakai, Trkay, Beck Freiwald, 2015).

A new species of the deep-sea shrimp genus Glyphocrangon A. Milne-Edwards, 1880 (Decapoda: Caridea: Glyphocrangonidae) from the South China Sea off Pratas Island.

A new species of the deep-sea caridean genus Glyphocrangon A. Milne-Edwards, 1880, G. obtusis n.sp., is described and illustrated on the basis of the material collected in the South China Sea off the Pratas Island. It appears close to G. hakuhoae Takeda Hanamura, 1994 and G. robusta Komai, 2004 among the 93 described species in Glyphocrangon. From G. hakuhoae, the new species is distinguished by the rostrum with less developed convexity on the dorsolateral margin and lacking transverse septa, and the less elevated median carinae on the pleomeres 15. From G. robusta, the new species differs in lacking transverse septa at the rostrum, the fourth carina on the carapace with the two anterior parts unaligned and the posterior part divided into four lobes. Molecular genetic analysis using the barcoding segment of the mitochondrial COI gene supports the establishment of the new species.

A new species of the infaunal alpheid shrimp genus Richalpheus Anker amp; Jeng, 2006 (Decapoda: Caridea) from Kagoshima, Japan.

A new species of the alpheid shrimp genus Richalpheus Anker Jeng, 2006 is described on the basis of 10 specimens collected from three locations in Kagoshima Prefecture, Kyushu, Japan. Richalpheus laeuadigitus n. sp. appears close to R. palmeri Anker Jeng, 2006 and R. dahabensis Anker Dworschak, 2007 among the three known congeners, but differs from R. palmeri in the proportionally wider telson and the more proximally located tip of the antennular stylocerite, and from R. dahabensis in the different configuration of the major cheliped fingers, in particular the possession of a well-developed bulge-like ridge on the occlusal margin of the dactylus. Two sequences of the mitochondrial 16S rRNA gene from two of the paratypes are newly obtained, and compared with that of R. palmeri downloaded from the GenBank database. The new species is the fourth representative of Richalpheus. Possible association between the new species and other infaunal invertebrates is suggested, although not specified.

Three new species of pagurid hermit crabs (Decapoda: Anomura: Paguroidea) from the Northern Mariana Islands, Micronesia.

We describe three new species of hermit crab of the pagurid genera, Catapagurus A. Milne-Edwards, 1880, Nematopagurus A. Milne-Edwards Bouvier, 1892 and Pagurixus Melin, 1939, on the basis of material collected during the scientific cruise to the Northern Mariana Islands conducted by the U.S. National Oceanographic and Atmospheric Administration (NOAA) in 2015. Catapagurus tenuilamina n. sp., referred to the C. ensifer Henderson, 1893 species group, appears close to C. granulatus Edmondson, 1951, but differs from the latter in the more slender ultimate article of the antennular peduncle, more slender dactyli of pereopods 2 and 3, and the possession of two dorsal subdistal spines in the meri of the pereopods. Nematopagurus marianicus n. sp. resembles N. gardineri Alcock, 1905 and N. lewinsohni Trkay, 1986, but is distinguished from the latter two by the characteristic dense setation on the upper part of the left cheliped carpus and by the elongate dactyli of pereopods 2 and 3 that lack a row of bristle-like setae on the dorsal margins. Pagurixus eminens n. sp. is referred to the P. boninensis Melin, 1939 species group and appears closest to P. annulus Komai Poupin, 2013, but is differentiated from the latter in the shape and ornamentation of the right coxa of pereopod 5 in the male as well as details of the colour pattern on the chelipeds and ambulatory legs. Partial sequences of the mitochondrial 16S rRNA gene from the three new species were sequenced and deposited in the GenBank database for future genetic and phylogenetic study.

Redescription of Pinnixa haematosticta Sakai, 1934, its transfer to Indopinnixa Manning amp; Morton, 1987, and a reappraisal of Indopinnixa kumejima Naruse amp; Maenosono, 2012 (Decapoda: Brachyura: Pinnotheridae).

The poorly known pinnotherid crab, Pinnixa haematosticta Sakai, 1934, is redescribed on the basis of female holotype and additional specimens, including males and females, from Japan. The male characters of the species are documented for the first time. The species is transferred to Indopinnixa Manning Morton, 1987 because the male pleonal somites 35 are functionally fused, the telson is wide, and the maxilliped 3 with the dactylus is distinctly longer than the propodus. Indopinnixa kumejima Naruse Maenosono, 2012 is morphologically very similar to I. haematosticta n. comb., but a molecular phylogenetic analysis using partial fragments of the mitochondrial 16S rRNA gene supports the hypothesis that the two taxa as distinct. Morphologically, the two species are differentiated by the shape of the pereopod 4 merus (proportionally wider in I. haematosticta n. comb. than in I. kumejima). Our findings suggest that I. haematosticta n. comb. and I. kumejima are geographically distinct: I. haematosticta appears restricted to the Japanese mainland (Honshu to Kyushu) and Ohsumi Islands, while I. kumejima occurs in the Ryukyu and Ogasawara Islands.