Redescription and molecular characterization of Mothocya parvostis Bruce, 1986 (Crustacea: Isopoda: Cymothoidae) parasitic on Japanese halfbeak, Hyporhamphus sajori (Temminck & Schlegel, 1846) (Hemiramphidae) with Mothocya sajori Bruce, 1986 placed into synonymy.

Two species of Mothocya have previously been recorded from Hyporhamphus sajori: M. parvostis Bruce, 1986 and M. sajori Bruce, 1986. Mothocya parvostis is re-described based on the ovigerous female type and additional materials collected from the host from in and around the type locality. Morphological re-examination of fresh specimens and the type materials together with genetic data show that the M. sajori and M. parvostis are the same species, differing primarily in size, therefore we have placed Mothocya sajori Bruce, 1986 into a junior synonym of Mothocya parvostis Bruce, 1986. Mothocya parvostis is characterized by the following combinations of characters: 1) body slightly to moderately twisted to one side; 2) pereonite 7 posterior margin moderately to deeply recessed; 3) uropodal rami extending to pleotelson posterior margin; and 4) uropod rami bluntly rounded, exopod 1.5 times as long as peduncle. The differences of four morphological features for M. parvostis and M. sajori was quantified. Furthermore, a total of 635 isopods infesting H. sajori were collected from all over Japan to conduct quantitative morphological and molecular sequence analyses (mitochondrial cytochrome c oxidase subunit I and 16S rRNA). Although the four quantitative features did not overlap between the two species in type specimens, all quantitative morphological values of newly collected specimens in this study did not display a bimodal distribution. In addition, our molecular analyses found only a single clade for our newly collected specimens in neighbor-joining tree.

Morphology of the gastric mill teeth in dotillid crabs (Crustacea: Brachyura: Dotillidae) from Indonesia.

The gastric mill is a prominent structure in the digestive system of brachyuran crabs, consisting of a median tooth plate and a pair of lateral tooth plates. Among crab species that are deposit feeders, the morphology and size of the gastric mill teeth are correlated with the preferred substrate types and food spectrum. In this study, we provide a detailed description of the morphology of the median and lateral teeth of the gastric mills in eight species of dotillid crabs from Indonesia, and compare them in relation to habitat preferences and molecular phylogeny. Ilyoplax delsmani, Ilyoplax orientalis, and Ilyoplax strigicarpus have comparatively simple shapes of their median and lateral teeth, with fewer teeth on each lateral tooth plate compared to Dotilla myctiroides, Dotilla wichmanni, Scopimera gordonae, Scopimera intermedia, and Tmethypocoelis aff. ceratophora, which have more complexly shaped median and lateral teeth, with a greater number of teeth on each lateral tooth plate. The number of teeth on lateral tooth correlates with habitat preference, that is, dotillid crabs inhabiting muddy substrata have fewer teeth on the lateral tooth plate, and those inhabiting sandy substrata have a more teeth. Phylogenetic analysis using partial COI and 16S rRNA genes supports that teeth morphology is similar among closely related species. Therefore, the description of median and lateral teeth of the gastric mill is expected to contribute to the systematic study of dotillid crabs.

The First Bopyrid Isopod from Hydrothermal Vents: Pleurocryptella shinkai sp. nov. (Isopoda: Epicaridea) Parasitizing Shinkaia crosnieri (Decapoda: Anomura).

Deep-sea hydrothermal vents are 'extreme' environments harboring diverse animal communities, powered by chemosynthesis. Though vent-endemic macrofauna have been a center of interest since their discovery in 1977, macroparasites have received little attention. Here, we report a bopyrid epicaridean isopod infesting the symbiotic munidopsid squat lobster Shinkaia crosnieri Baba and Williams, 1998 from three vent fields of Okinawa Trough, and describe it as Pleurocryptella shinkai sp. nov. Although morphologically close to the congeners Pleurocryptella formosa Bonnier, 1900, Pleurocryptella wolffi Bourdon, 1972, and Pleurocryptella altalis Williams, Boyko, and Marin, 2020, both females (via body proportion and characters of barbula, antennae, pleopods, and pleomeres) and males (via features of the head, pleomeres, and uropods) of the new species exhibit distinctive characters. Phylogenetic reconstruction based on the 18S rRNA gene (850 bp) was insufficiently resolved to clarify the relationship of different epicaridean lineages or the exact position of P. shinkai sp. nov., but it recovered P. shinkai sp. nov. in a distant position from the type genus of Pseudioninae, indicating non-monophyly of this subfamily. Crustaceans are successful in vents but this is only the second vent epicaridean reported, after Thermaloniscus cotylophorus Bourdon, 1983 from the East Pacific Rise described from a single cryptoniscus larva. As such, this is the first report of a vent bopyrid isopod and the first vent epicaridean with a known host. Some epicaridean lineages have adapted to tolerating the conditions of hydrothermal vents, and future research will likely uncover more epicarideans and other interesting parasites from these extreme habitats.

A new species of Expanathura (Crustacea: Isopoda: Anthuroidea) from Iriomote Island, Japan, with a note on male polymorphism.

We describe Expanathura monile sp. nov. from Iriomote Island, Okinawa, Japan, northwestern Pacific. This species resembles E. collaris, E. macronesia, and E. haddae in having very broad uropodal rami, a broad telson, and a moderately shortened pleopod 1 endopod, but differs from these three species in the female having (1) the head with a dorsal V-shaped band of brown pigmentation, (2) the antennular flagellum with 34 articles, (3) antennal peduncular article 2 with an outer triangular projection, (4) the uropodal endopod longer than wide, (5) the uropodal exopod with an acute triangular projection, (6) an oval telson, and (7) the posterolateral setae on the telson similar in length. We present a revised key to known species in the genus Expanathura and briefly discuss the male polymorphism observed in E. monile.

Parasitism-Induced Intersexuality in a Sexually Dimorphic Varunid Crab, Ptychognathus ishii (Decapoda: Varunidae).

Although many animals that perform sexual reproduction exhibit sexual dimorphism, individuals with intersex traits between the traits of males and females appear in some species, depending on environmental factors. Ptychognathus ishii, a varunid crab, exhibits distinctive sexual dimorphism in the morphology of its abdomen, chelipeds and setal tufts on the chelipeds. In this study, however, we report for the first time that intersex individuals with intermediate characters between those of males and females were occasionally found in wild populations. Morphological features of intersex individuals are described. Their taxonomic positions are identified based on DNA sequences of part of the mitochondrial cytochrome c oxidase I (COI) gene. It was shown that the intersexuality was induced by entoniscid parasites, because all intersex individuals were parasitized by entoniscid isopods, identified as Entionella sp. The apparent correlation between parasitism and morphological anomalies suggests that the parasitic isopods affect physiological conditions, leading to the feminization of male hosts.

Seborgia cavernicola sp. nov. from a submarine cave on Okinawa Island, Ryukyu Islands, southwestern Japan (Crustacea, Amphipoda, Seborgiidae).

A new seborgiid, Seborgia cavernicola sp. nov. is described from a submarine cave in Okinawa Island, Ryukyu Islands as the first record of the family from Japan. This species differs from its congeners by the following combination of characters: body without microspinules; eyes fainted, without ommatidia; epimeral plates with posterodistal angle produced into pointed process; main flagellum of antennule 4-articulate; article 2 of main flagellum of antennule longest; propodus of gnathopod 2 as long as wide; gland cone of antenna directed anteriorly; maxilla bilobed; uropod 3 biramous; and telson without setae and setules. A key to species of the genus is provided.

Heteromysoides taramensis, a new species of mysid (Mysida: Mysidae) from an anchialine cave on Tarama Island, Ryukyu Islands, southwestern Japan.

Heteromysoides taramensis, a new species of the family Mysidae (Mysida) is described from an anchialine cave on Tarama Island, Ryukyu Islands, southwestern Japan. This species differs from its congeners by the following combination of characters: eyes subrectangular in dorsal aspect without process; cornea developed; telson distally rounded, 1.3 times as long as maximum width, with 5 or 6 pairs of simple spines distolaterally, 1 pair of long simple spines subapically and 1 pair of short simple spines apically; antennal scale elongated elliptical, extending to distal margin of antennular peduncle; antennal sympod with distomesial corner produced into blunt tooth; and endopod of third thoracopod with simple, not subchelate, termination.

A new species of the mesopelagic isopod genus Xenuraega Tattersall, 1909 (Crustacea: Isopoda: Aegidae) from Japan, the second species in the genus.

Xenuraega bythionekta sp. nov., is described from a single specimen taken off southern Japan. It is the second species of Xenuraega Tattersall, 1909, and extends the known range of the genus from North Atlantic to the northern Pacific Ocean. The species is characterized by the posteriorly narrowed pleotelson, and both uropodal rami being elongate and provided with a mass of long plumose setae. Xenuraega bythionekta sp. nov. is known only from the type locality, Kagoshima Prefecture, southern Japan at a depth of 1178-1179 m.

A new species of Aspidophryxus (Isopoda, Dajidae), ectoparasitic on Mysidella hoshinoi (Mysidae) in Japan.

A new dajid, Aspidophryxus izuensissp. n., is described from seven females and six males found infesting the dorsal carapaces of specimens of Mysidella hoshinoi Shimomura, 2016 (Mysidae: Mysidellinae) associated with an unidentified species of sea anemone (Haloclavidae) from Izu-Oshima Island, Sagami Sea, central Japan. Aspidophryxus izuensis sp. n. differs from its congeners in having a body length about as long as wide, widest at the anterior part in females; an elongate frontal part of the cephalon, half as long as wide in females; the frontal margin of the cephalon exceeding the anterior margins of lateral lamellae in females; an unsegmented, vermiform, elongate pleon in females; and a uropod composed of a protopod and an inner and outer ramus in males. A key to worldwide species in the genus is provided.

Mysidella hoshinoi, a new species from Izu-Oshima Island, Japan (Crustacea, Mysidae, Mysidellinae).

A new mysid, Mysidella hoshinoisp. n. is described from Izu-Oshima Island, Sagami Sea, central Japan. This species differs from its congeners in having a posterodorsal finger-like papilla on the eyestalk, five peculiar spines terminating in plumed seta on outer margin of carpopropodus of endopod of first thoracopod, and uropodal endopod bearing 27 spines on inner margin.

DNA barcoding and morphological analyses revealed validity of Diadema clarki Ikeda, 1939 (Echinodermata, Echinoidea, Diadematidae).

A long-spined sea urchin Diadema-sp reported from Japanese waters was genetically distinct from all known Diadema species, but it remained undescribed. Extensive field surveys in Japan with molecular identification performed in the present study determined five phenotypes (I to V) in Diadema-sp according to the presence and/or shape of a white streak and blue iridophore lines in the naked space of the interambulacral area. All phenotypes were distinct from Diadema setosum (Leske, 1778) and Diadema savignyi (Audouin, 1829), of which a major type (I) corresponded to Diadema clarki Ikeda, 1939 that was questioned and synonymized with Diadema setosum by Mortensen (1940). The holotype of Diadema clarki has not been found, but three unlabeled dried tests of Diadema were found among Ikeda's original collection held in the Kitakyushu Museum of Natural History and Human History, Fukuoka, Japan. A short mtDNA COI fragment (ca. 350bp) was amplified from one of the tests, and the nucleotide sequence determined (275bp) was nearly identical with that of Diadema-sp. Arrangements of the primary tubercles on the coronal plates in Diadema-sp and the museum specimen also conformed with Diadema clarki, indicating that Diadema-sp is identical to Diadema clarki and a valid species. Narrow latitudinal distribution (31°N to 35°N) of Diadema clarki in Japan was observed, where it co-existed with abundant Diadema setosum and rare Diadema savignyi. No Diadema clarki was found in the southern islands in Japan, such as Satsunan Islands to Ryukyu Islands and Ogasawara Island, where Diadema setosum and Diadema savignyi were commonly observed.

Epimeria abyssalis sp. n. from the Kuril-Kamchatka Trench (Crustacea, Amphipoda, Epimeriidae).

A new deep-sea epimeriid, Epimeria abyssalis is described from the Kuril-Kamchatka Trench, in the northwestern Pacific. This species differs from its congeners in having a short rostrum and a telson with deep and narrow Y-shaped excavation. Epimeria abyssalis is the deepest recorded Epimeria species. A key to the north Pacific species of Epimeria is provided.

Two new species of Asellota (Crustacea, Isopoda) from coral reefs on Iriomote Island, Okinawa, Japan.

Pleurocope iriomotensis sp. n. and Prethura tuberculata sp. n. are described from Iriomote Island, Ryukyu Archipelago, southern Japan. These are the first records of Pleurocope from the Pacific and of Prethura from the Asian Pacific coast. Pleurocope iriomotensis differs from its congeners in having lateral spine-like processes on pereonite 4 and coxal plates of pereonite 7. Prethura tuberculata can be distinguished from its single congener in having a lateral short projection of protopod of pleopod 2.

A new species of Enterognathus (Copepoda, Cyclopoida, Enterognathidae) collected from the Seto Inland Sea, western Japan.

A new species of the endoparasitic copepod Enterognathus (Cyclopoida, Enterognathidae) is described from a crinoid host in the Seto Inland Sea, western Japan. This is a third species of the genus and its first occurrence in the Pacific Ocean. The new species is distinguished from two previously known congeners by the morphology of the body somites, caudal rami, antennae and legs. Crinoid parasites belonging to Enterognathus and the closely related genus Parenterognathus have a broad distribution from the northeastern Atlantic through the Red Sea to the West Pacific.

A new species of Halacarsantia Wolff, 1989 (Crustacea, Isopoda, Asellota, Santiidae) from Wistari Reef, southern Great Barrier Reef, Australia.

Halacarsantia acutasp. n. is described from Wistari Reef, Capricorn Group, southern Great Barrier Reef, the first record of the genus from Australia. The new species differs from its congeners in having antenna flagellum composed of 8 articles; epipod apically acute, without setae, broad maxilliped endite and pereopod 1 basis with a short projection. A key to species of the genus is provided.

Toxicity Assessment of the Xanthid Crab Demania cultripes from Cebu Island, Philippines.

Several cases of poisoning resulting in human fatalities and stemming from the ingestion of coral reef crabs have been reported from the Indo-Pacific region. We assessed the toxicity of the unidentified xanthid crab collected from the Camotes Sea off the eastern coast of Cebu Island, central Visayas region of Philippines from the food hygienic point of view. All seven specimens, which were identified with Demania cultripes, collected in 2006 were toxic to mice irrespective of the season of collection and induced paralytic symptoms typical of tetrodotoxin (TTX) and paralytic shellfish poison (PSP). The activity was expressed in mouse unit (MU) being defined as the amount of TTX to kill a 20 g ddY male mice in 30 min after i.p. injection. Toxicity scores for viscera and appendages of specimens were 18.2 ± 16.0 (mean ± S.D.) and 4.4 ± 2.6 MU/g, respectively. The highest individual toxicity scores observed for viscera and appendages were 52.1 and 7.7 MU/g, respectively. The frequency of toxic samples was 100%. Toxin profiles as determined by high-performance liquid chromatography-fluorescent detection analysis (HPLC-FLD) revealed that TTX was the main toxic principle accounting for about 90% of the total toxicity along with 4-epi TTX and 4,9-anhydroTTX. Furthermore, gas chromatography-mass spectrometry (GC-MS) analysis revealed mass fragment ion peaks at m/z 376, 392 and 407, which were characteristic of the quinazoline skeleton (C9-base) specific to TTX. In addition, only a small amount of PSP containing gonyautoxins1-4 and hydroxysaxitoxin was detected. To our knowledge, this is the first report presenting evidence of occurrence of TTX and PSP in the xanthid crab D. cultripes inhabiting waters surrounding Cebu Island. From food hygienic point of view, people in coastal areas should be warned of the potential hazard of this crab in order to prevent its intentional or accidental consumption.

Prodajus curviabdominalis n. sp. (Isopoda: Epicaridea: Dajidae), an ectoparasite of mysids, with notes on morphological changes, behaviour and life-cycle.

Adults and larvae of a new ectoparasitic isopod, Prodajus curviabdominalis n. sp., are described from the mysid Siriella okadai Ii collected from the Seto Inland Sea, western Japan. The adult female is found within the host marsupium with the cephalon directed posteriorly, whereas the dwarf adult male attaches to the ventral surface of the female pleon. The cryptoniscid larva usually attaches to the second or third abdominal somite of the host, using an oral sucker. Mature adults of the new species are distinguished from all other congeners by: pleon of ovigerous female strongly curved dorsally, with large swellings on ventral side; pereon of ovigerous female narrow; exopods on male uropods present; male pleon short and thick. This is the third record of a member of the Dajidae from Japan. The behaviour of the cryptoniscid larvae of the new species on the host mysid was also observed using a video camera. Larvae moved from the first attachment site, usually the second or third abdominal somite of the host mysid, into the marsupium. When host oostegites were not fully developed, larvae entered beneath the host carapace until her marsupium was fully formed. The host infected by a female P. curviabdominalis moved the oostegites rhythmically, an action which may aid the respiration of the parasite.