Two new species and new host and distribution records of Gnathia Leach, 1814 (Crustacea, Isopoda, Gnathiidae) from Western Australia and the Great Barrier Reef, Australia.

Gnathiaantennacrassasp. nov. from seagrass beds off Rottnest Island, Western Australia is the first record of any gnathiid from the entirety of Western Australia; the male can be distinguished from congeners by the stout peduncular articles of the antenna. Gnathiataurussp. nov. is described from two adult specimens reared from praniza larvae found infecting elasmobranch fishes at Heron Island, southern Great Barrier Reef; the males can be distinguished from all congeners by the dorsally strongly elongate mandibles and smoothly rounded mediofrontal process on the anterior part of cephalosome. Gnathiaaff.maculosa Ota & Hirose, 2009 is recorded from Australia, together with further records of G.trimaculata Coetzee, Smit, Grutter & Davies, 2009 and G.grandilaris Coetzee, Smit, Grutter & Davies, 2008, all from elasmobranch fishes.

Investigating the diversity of bioluminescent marine worm Polycirrus (Annelida), with description of three new species from the Western Pacific.

Bioluminescence, a phenomenon observed widely in organisms ranging from bacteria to metazoans, has a significant impact on the behaviour and ecology of organisms. Among bioluminescent organisms, Polycirrus, which has unique emission wavelengths, has received attention, and advanced studies such as RNA-Seq have been conducted, but they are limited to a few cases. In addition, accurate species identification is difficult due to lack of taxonomic organization. In this study, we conducted comprehensive taxonomic survey of Japanese Polycirrus based on multiple specimens from different locations and described as three new species: Polycirrus onibi sp. nov., P. ikeguchii sp. nov. and P. aoandon sp. nov. The three species can be distinguished from the known species based on the following characters: (i) arrangement of mid-ventral groove, (ii) arrangement of notochaetigerous segments, (iii) type of neurochaetae uncini, and (iv) arrangement of nephridial papillae. By linking the bioluminescence phenomenon with taxonomic knowledge, we established a foundation for future bioluminescent research development. We also provide a brief phylogenetic tree based on cytochrome c oxidase subunit I (COI) sequences to discuss the evolution of bioluminescence and the direction of future research.

Partial redescriptions of three holothurians with hook papillae (Apodida: Chiridotidae): Taeniogyrus japonicus (Marenzeller, 1882), T. dendyi (Mortensen, 1925), Scoliorhapis theelii (Heding, 1928).

New specimens of Taeniogyrus japonicus (Marenzeller) were collected from Iwami coast and Sado island of the Sea of Japan. According to detailed observations of external and internal organs, we transferred T. japonicus, T. dendyi (Mortensen), and Scoliorhapis theelii (Heding) to the newly revived genus Scoliodota, with a large retractor organ and hook papillae as major diagnostic characters. We also concluded that Scoliorhapis dianthus Solis-marin et al. is a synonym of T. japonicus. Our molecular phylogeny and genetic distance analysis showed that specimens from Iwami and specimens from Sado of T. japonicus form a monophyletic clade, indicating that they are most likely the same species despite their morphological variation. The phylogenetic analysis also indicated that T. japonicus forms a sister group relationship with Taeniogyrus verruculosus Yamana Tanaka and Scoliorhapis sesokoensis Yamana Tanaka, suggesting that Taeniogyrus is not monophyletic. Taken together, these results brought new insights to sea cucumber diversity in Japanese waters.

First Record of Elasmobranch Hosts for the Gnathiid Isopod Crustacean Thaumastognathia: Description of Thaumastognathia bicorniger sp. nov.

Gnathiid larvae (Crustacea; Isopoda; Gnathiidae) infesting elasmobranch and holocephalan fishes from mainly bathyal depths off Suruga Bay, off Kume-jima Island, and five sites from off Tokyo Bay to Shimoda City, Japan were examined. A total of 1460 gnathiid larvae were sampled from 87 host individuals belonging to seven families and 10 species. The morphology of these larvae was distinguishable from other gnathiid species by the head appendages. These larvae presented two pigmentation patterns, stripes or spots, on their dorsal thoraxes in live specimens. Furthermore, they were determined as the second and third stage praniza larvae on the basis of allometric variance of maximum head and abdomen widths. A third stage praniza with stripe pigmentation metamorphosed into an adult male and could be identified as a new species of the genus Thaumastognathia Monod, 1926. The duration between detachment from the host and metamorphosis into male adult required 204 days. This paper describes Thaumastognathia bicorniger sp. nov. on the basis of P3/stripe larvae and the male adult. This report is the first record of the larva and host information for a species of Thaumastognathia.

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.

Description of female adult and praniza larva of Tenerognathia visus Tanaka, 2005 (Crustacea; Isopoda; Gnathiidae) with notes on mating behavior.

Male adults of gnathiid isopods (Crustacea; Isopoda; Gnathiidae) have remarkably developed rectangular-shaped cephalosomes and mandibles in most species. Tenerognathia visus Tanaka, 2005 belongs to a monospecific genus having remarkable characters in male morphology; reduced mandibles and large eyes occupying the whole of an elliptical cephalosome. The original description of T. visus is based on male adult specimens from coral rubble. This study found adult males and their larvae of T. visus attracted by light. Furthermore, specimens of female adults were observed by laboratory rearing of praniza larvae. In this study, morphologies of larvae and female adults of T. visus are described and notes on mating behavior in a laboratory aquarium are provided.

Pigmentation patterns are useful for species identification of third-stage larvae of gnathiids (Crustacea: Isopoda) parasitising coastal elasmobranchs in southern Japan.

Previous studies from southern Japan reported larval stages of eight gnathiid isopod species parasitising coastal elasmobranchs. Since gnathiid larvae of these different species closely resembled each other, it was necessary to obtain specimens of free-living adult males for identification to the species level. This was achieved by allowing larvae of the final stage to moult into adult males. From these males, specimens of a species new to science were discovered and described here as Gnathia rufescens n. sp. The main differentiating characteristics of G. rufescens n. sp. are: (i) the apex of pleotelson is oval shaped; (ii) the dorsal sulcus is wide in the posterior part; and (iii) the article 3 of the pylopod is not reduced in the male. Additionally, this paper summarises the specific pigmentation patterns of third-stage larvae of the new species and eight previously described species. Furthermore, host records and host use by the gnathiids were summarised based on data from 158 hosts and over 4,500 gnathiid samples; these are discussed with a focus on host-specificity of the nine gnathiid species studied.

Three new gnathiid species with larvae ectoparasitic on coastal sharks from southwestern Japan (Crustacea: Isopoda).

Gnathiid larvae were collected from the gill chambers of coastal sharks in southwestern Japan. Some were reared in a laboratory aquarium and successfully metamorphosed into adults. Morphological observations of the adult males identified three undescribed species, which are designated Gnathia albipalpebrata n. sp., G. parvirostrata n. sp., and G. dejimagi n. sp. on the basis of their larval morphologies and pigmentation patterns. 

Redescription of five gnathiid species from Japan (Crustacea: Isopoda).

Five gnathiid species from Japan are redescribed based on14 holotypes, their paratypes, topotypes, and new materials. Observations of these specimens revealed that Caecognathia kikuchii (Nunomura, 1992) should be transferred to genus Elaphognathia and Caecognathia nasuta (Nunomura, 1992) to genus Gnathia. Furthermore, Caecognathia amakusaensis Nunomura, 1992, C. saikaiensis Nunomura, 1992, Gnathia azumai Nunomura, 2012a, G. quadricephala Nunomura, 2012a, and G. recticornata Nunomura, 2012a are considered to be junior synonyms of E. kikuchii. Gnathia hirayamai Nunomura, 1992, G. nagasakiensis Nunomura, 2012a, G. shijikiensis Nunomura, 2012a, and G. brevicephala Nunomura, 2012a are considered to be junior synonyms of G. nasuta. Moreover, Gnathia sanrikuensis Nunomura, 1998 and G. mutsuensis Nunomura, 2004 are redescribed. Gnathia bungoensis Nunomura, 1982 is not completely redescribed because the key characteristics were lacking. The geographical records of these species are provided.

A new species of Gnathia (Isopoda: Cymothoida: Gnathiidae) from Okinawajima Island, Ryukyu Archipelago, southwestern Japan.

Gnathia limicola sp. nov. is described from Okinawajima Island, Ryukyu Archipelago, southwestern Japan. Burrows of this species were found in a small intertidal creek bank on a muddy tidal flat near mangrove trees. Adult males differ from those of other Gnathia species in the following features: (1) fine setae cover peduncle articles 1 and 2 of antenna 1, peduncle articles 1-3 of antenna 2, and the erisma of the mandibles; (2) the ventral frontal border of the cephalon is medianly notched, and the lateral parts extend beyond the dorsal frontal border; and (3) the penes are fused into a thin rectangular blade directed posteriorly. Adult females and praniza larvae were also distinguished morphologically from other Gnathia species. Based on field and laboratory observations, the mating behavior of this species appears similar to that of Paragnathia formica (Hesse, 1862), which inhabits salt marshes in Europe and North Africa.