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We describe a new tanaidid species, Zeuxo molybi sp. n., from Kominato, Chiba, Japan. Zeuxo molybi closely resembles the Japanese congener Zeuxo ezoensis, but differs in having (1) the pereopod-1 carpus without dorsodistal spiniform setae; (2) two or three ventrodistal simple setae on the pereopod-1 propodus in females, and three or four in males; and (3) the pereopod-6 propodus with four or five flattened denticulate setae. The two species also differ in the pattern of dorsal pigmentation on the carapace. Kimura 2-parameter distances between the two species were 15.6–16.9% for the cytochrome c oxidase subunit I (COI) gene and 2.8% for the 18S rRNA gene; the former value is much greater than intraspecific distances previously reported for Z. ezoensis (0–1.5%), confirming our conclusion from morphology that Z. molybi and Z. ezoensis are not conspecific. In a COI-based maximum-likelihood phylogenetic tree, the Japanese taxa Z. molybi, Z. ezoensis, and Z. cf. normani did not form a clade. [ABSTRACT FROM AUTHOR]

A new species of Leptostraca, Sarsinebalia agoensis sp. nov., from Ago Bay, Japan is described from specimens found at a depth of 120 m. The new species differs from other known Sarsinebalia species as follows: the compound eye has three distal lobes; the anterior margin of the first antennal segment has one distal process covered with setae; and the lateral margin of pleopod 1 exopod bears 5--6 simple, robust spines. A taxonomic key to all species of Sarsinebalia is also provided. [ABSTRACT FROM AUTHOR]

We describe Paradoxapseudes shimojiensis sp. nov. from a submarine limestone cave at Shimoji-jima Island, Ryukyu Islands, southwestern Japan. This species resembles five species (P. basibidens, P. bassoprofundo, P. bermudeus, P. edgari, and P. heroae, among 17 congeners) that bear a long pleotelson, but differs from them in having (i) a naked antennal article 1, (ii) the maxillipedal basis with one inner distal plumose seta, (iii) the chelipedal basis with one dorsodistal and one ventro-subproximal simple setae, (iv) the pereopod-1 basis with four dorsal simple setae longer than the width of the pereopod-1 basis, but without ventrodistal spiniform setae, (v) the pereopod-1 merus with three mid-inner ventral simple setae, and (vi) the pleopodal protopod with two inner plumose setae. We determined partial nucleotide sequences for the cytochrome c oxidase subunit I (COI) and 18S rRNA (18S) genes in P. shimojiensis for future use in DNA barcoding and phylogeny. Paradoxapseudes shimojiensis has serial ridges on the inner surfaces of the left and right chelipedal bases that quite resemble the stridulatory organs in harvestmen (Opiliones); by analogy, we speculate that these ridges may be stridulatory sound-producing organs. Two specimens had both a fully-developed marsupium and genital cone, suggesting that P. shimojiensis is simultaneously hermaphroditic. [ABSTRACT FROM AUTHOR]

A new species of Leptostraca, Nebalia tagiri sp. nov. is described and illustrated. This species was sampled from 200 m depth at a hydrothermal field in Wakamiko Caldera of Kagoshima Bay, Japan. Nebalia tagiri sp. nov. is different from known Nebalia species as follows: rostral length 2.4 times as long as width; article 4 of antennule with 3-5 robust distal spines; antennular scale approximately twice as long as wide; article 3 of antenna with eight spines and nine spine-like setae along proximal half, two thin setae and six spine-like setae on external lateral face, six spines and four simple setae on distal margin; article 1 of second maxilla longer than article 2; article 2 of mandibular palp with two thin setae; exopod of pleopod 1 with 21 spines along lateral margin; furcal rami longer than combined length of pleonite 7 and telson; rounded denticles of pleonite 6 and 7; anal-plates 'shoulder' not distinct. Furthermore, this specimen is the first genus Nebalia found in the hydrothermal vent. The distribution and ecology of this new species is also discussed and a key to all species of Nebalia is provided. [ABSTRACT FROM AUTHOR]

Intertidal isopods use a variety of living or non-living objects as habitats, although only a few studies have been made on their ecological function and significance. In the present study, the habitat utilization by the sphaeromatid isopod, Dynoides dentisinus was recorded based on observations on intertidal rocky shores in the warm temperate zone of Japan during the period from 2014 to 2018. The adults of this species have a remarkable sexual dimorphism in the morphology of their armature: adult males possess an elongate pleonal process, like a large horn, on the dorsal side of the pleon and have large uropods. On the other hand, females do not have such a horn, and the uropods are small. Differences in habitat use were seen according to the stage in the life history of the species. Juveniles lived on, or amongst, algae and were sometimes associated with molluscs such as chitons, limpets and whelks. Adults inhabited the cryptic habitats such as gaps in algal holdfasts, oscula of demosponges, dead barnacle shells, cavities of dead corals, and crevices in sand rocks. Generally, a single adult male was present in each cryptic habitat, keeping head in down position, and one or more females cohabited inside with the male. These suggest that D. dentisinus has a biphasic life history; juveniles live and feed on algal cover or use the spaces between the ventral sides of the molluscs and the surfaces of the rocks as a refuge from desiccation. Adults breed in the cryptic habitats, forming a polygynous group. [ABSTRACT FROM AUTHOR]

The article presents a study that investigates the crustacean species in Japan. The author mentions that two species of crustaceans discovered belong to the Axiida family and these include Calaxius izuensis Komai and Ambiaxiopsis altimanus Komai. Moreover, the attributes of the two new crustaceans are also mentioned.

The euphausiid ectoparasitic isopod, Heterophryxus appendiculatus G. O. Sars, 1885, is recorded for the first time from the Pacific Ocean, based on specimens collected from off the Nansei Islands, Japan. This species is distinguished from other congeners by the nearly straight frontal margin of the cephalon. This study provides additional information on this species, including a new host, description, coloration, and scanning electron micrographs. [ABSTRACT FROM AUTHOR]

Four new species of decapods and one new species of isopod are described from the Barremian (Lower Cretaceous) Arida Formation in Wakayama Prefecture, Japan. Xanthosia sakoi new species (Brachyura, Etyidae) and Palaega yamadai new species (Isopoda, Cirolanidae) represents the first record of each genus from the North Pacific realm. Xanthosia sakoi is the oldest member of this genus. Eryma nippon new species (Astacidea, Erymidae) is the first Cretaceous record for the genus Eryma from the North Pacific realm. Hoploparia natsumiae new species (Astacidea, Nephropidae) comprises the second record of this genus from the Barremian of Japan. Eomunidopsis kinokunica new species (Anomala, Galatheidae) represents the oldest record from the North Pacific realm. The systematic position of the family Etyidae is discussed and the Etyidae is elevated to full superfamily status. [ABSTRACT FROM AUTHOR]

Spatial and seasonal distribution pattern, life history and production of three species of Neomysis (Mysidacea) which commonly occur in northwestern subarctic Pacific coastal waters, were investigated throughout the year in the Akkeshi-ko estuary, northern Japan. The most abundant species Neomysis awatschensis (annual mean density: 179.8 inds. m−2, biomass: 108.8 mg DW m−2) occurred at the inner part of the estuary including low salinity areas with no clear preference for the seagrass bed. The second most abundant Neomysis mirabilis (mean density: 95.8 inds. m−2, biomass: 90.1 mg DW m−2) occurred at relatively saline seagrass site throughout the year. Occurrence of Neomysis czerniawskii in the estuary was limited to the seagrass bed during summer when their population mainly consisted of juveniles, suggesting that this species is a seasonal migrant between the estuary and the marine environment. Both N. awatschensis and N. mirabilis populations were composed of two generation types, a larger sized overwintering and smaller sized spring/summer generations; however, each species had a different reproductive strategy. N. awatschensis was characterized by fast growth to maturity at a smaller size than N. mirabilis with a relatively high fecundity during warm season, suggesting that this species is an r-strategist which can utilize opportunistically a wide variety of habitats. In contrast, the seagrass bed resident N. mirabilis was a K-strategist which matures at a larger size producing fewer but larger offspring. The annual production of N. awatschensis (0.57–0.70 g DW m−2, mean of the whole estuary) and N. mirabilis (0.58–0.68 g DW m−2, mean of the seagrass bed) at their respective habitats was comparable. Consequently, species-specific life history and distribution pattern are concluded to allow Neomysis spp. to coexist in the estuary and the high carrying capacity of seagrass bed is suggested to contribute to maintain their high biomass level. [ABSTRACT FROM AUTHOR]

A new ingolfiellid amphipod, Ingolfiella inermis n. sp. is described from a coral sandy beach of Okinawa, southern Japan. The new species differs from its congeners in the following characters: head, pereionites, pleonites, and urosomites without dorsal setae; fleshy and moderately long telson; broad carpus of gnathopod 2 with some minute teeth and long palmar angle spine; dactyli of gnathopods 1 and 2 each with 4 teeth; pereiopod 7 longer than the other pereiopods; uropod 1 longer than uropod 2; outer ramus of uropod 1 longer than 1/2 inner ramus. [ABSTRACT FROM AUTHOR]

The pontoniine shrimp, Periclimenes adularans Bruce, 2003, previously known only by its type specimens from Australia, is recorded on the basis of some recently collected specimens from the East China Sea coast of Kyushu and the Ryukyu Islands, Japan as well as from the southwestern coast of Taiwan. The species' coloration in life is reported for the first time. Although the host species of P. adularans has not previously been recorded, the present study shows that this shrimp is associated with sea anemones, viz., Cerianthus filiformis Carlgren, 1922 and Megalactis hemprichii Ehrenberg, 1834. Supplementary morphological information on P. adularans is also given. [ABSTRACT FROM AUTHOR]

A new species of Palaumysis, P. pilifera, the fourth species of the genus, is reported from two submarine caves of Okinawa, southwestern Japan. The new species closely resemble the two species previously reported from the Pacific by possessing a multi-segmented inner flagellum in the antennule, but it differs from them in having the terminal spine of the male fourth pleopod bearing rows of fine setules (or hairs) near midlength, as opposed to a naked spine in the latter two species. The present discovery extends the geographical limit of the genus further north to 26 ° N in the western North Pacific. Additional information on the colour pattern and ecological feature of P. simonae B$\backslash check\{\; a\}$cescu & Iliffe, 1986, are provided on the basis of newly collected material from a submarine cave on Palau. [ABSTRACT FROM AUTHOR]

We describe a new typhlotanaid species, Hamatipeda kohtsukai sp. nov., collected from between 167 and 488 m depth in the Sagami Sea, Japan. This is the first record of Hamatipeda from the northern hemisphere. Hamatipeda kohtsukai resembles Hamatipeda trapezoida from the Subantarctic region in having pereonites 1-3 widest anteriorly (not rectangular), but differs from it in the length ratio of antennal articles 4/5; the number of setae on the dactyli of pereopods 1-3, ischia of pereopods 4-6, and carpi of pereopods 4-6; the shape of the unguis of pereopods 4-6; and the shape of the uropodal endopod. We determined partial sequences for the cytochrome c oxidase subunit I (COI; cox1) and 18S rRNA (18S) genes in H. kohtsukai . A phylogenetic reconstruction based on the 18S sequences recovered a highly supported Typhlotanaidae clade containing H. kohtsukai and Typhlotanais mixtus , with Paranarthrura sp. (Agathotanaidae) as the sister taxon. A key to species of Hamatipeda is presented.