Redescription of Taeniacanthus aulacocephali (Copepoda: Cyclopoida: Taeniacanthidae) parasitic on Uranoscopus japonicus Houttuyn (Uranoscopidae) from Pacific coast, Japan, with adaptation of the non-destructive DNA technique.

Taeniacanthus aulacocephali Izawa, 2021 (Copepoda: Cyclopoida: Taeniacanthidae) was redescribed from the branchial cavity and gill filaments of Uranoscopus japonicus Houttuyn (Perciformes: Uranoscopidae) collected from the Pacific coast of the Kochi and Wakayama prefectures, Japan. This is the second record of the copepod, and the finding from U. japonicus represents the new host record. The species is characterized by several distinguishing features: 1) a decrease in the width of the habitus between the second and fourth pedigerous segments; 2) the ratio of prosome/body length; 3) the presence of eight setae on the exopodal terminal segment of leg 2; 4) an un-bifurcated maxilliped claw surrounded by 14-28 transverse ridges; and 5) the presence of an inner coxal seta on legs 2 and 3. The newly collected specimens were subjected to a modified non-destructive DNA extraction method and morphological description based on the same copepod individual, while preserving a morphologically describable specimen. Sequences of 18S rDNA, 28S rDNA and the mitochondrial cytochrome c oxidase subunit 1 mitochondrial gene (cox1) were obtained.

A new species of the genus Paradistomum (Platyhelminthes: Trematoda) from Iwasaki's snail-eating snake Pareas iwasakii, with a note on morphological variations of Paradistomum megareceptaculum (Tamura, 1941).

Dicrocoeliid trematodes were detected from Iwasaki's snail-eating snake Pareas iwasakii in Iriomote Island, Okinawa Prefecture, Japan, and described as a new species Paradistomum dextra n. sp. in the present study. This new species can be distinguished from the type series of the other members of the genus based on size of eggs and morphological characteristics of body, oral and ventral suckers, and reproductive organs. However, the new species was hard to distinguish from Paradistomum megareceptaculum infecting snakes in Japan, including Iriomote Island where is the type locality of the new species, because it is closely similar to some part of the broad range of morphological variations in P. megareceptaculum. On the other hand, a partial sequence of 28S ribosomal DNA clearly distinguished these two species. Moreover, the new species' host snake Pareas iwasakii is reported to exclusively feed on land snails while host snakes of P. megareceptaculum feed on small vertebrates, indicating that the new species is also ecologically different from P. megareceptaculum. We also redescribed P. megareceptaculum based on adults sampled in this study and past studies to record the morphological variations of this species.

Description of a new species, Pseudodiscocotyla mikiae n. sp. (Monogenea: Discocotylidae) parasitic on gills of Pristipomoides filamentosus from off Okinawa-jima island in Japan, with redescription of Pseudodiscocotyla opakapaka.

Two species of Pseudodiscocotyla Yamaguti, 1965 (Monogenea: Discocotylidae) were collected from crimson jobfish Pristipomoides filamentosus (Valenciennes) (Perciformes: Lutjanidae) off Okinawa-jima island, southern Japan. Pseudodiscocotyla opakapaka is redescribed and represents the first Japanese record. A new species, Pseudodiscocotyla mikiae n. sp., differs from Ps. opakapaka in the absence of spines around the male genital pore, the shape of the vaginal pore, the presence of spines inside the vaginal pore, and the shape of the clamp. The locations of the male genital atrium and the vaginal pore in both species were similar, and the observed armament differences of the male copulatory organ are therefore presumed to establish reproductive isolation. The phylogenetic trees for the Mazocraeidea based on the partial 28S rDNA sequences were created using new sequences of Pseudodiscocotyla mikiae n. sp., and Discocotylidae formed a sister group with the species Diclidophoridae, Macrovalvitrematidae, and Plectanocotylidae. Pristipomoides filamentosus is widely distributed across the Indo-Pacific, and Pseudodiscocotyla mikiae n. sp. could share the distribution of the host.

Capsalid monogeneans of fishes from the Seto Inland Sea, Japan: Description of Benedenia kobudai n. sp. parasitic on Semicossyphus reticulatus (Perciformes: Labridae).

The Seto Inland Sea, the largest inland sea in Japan, is a rich fishery with high biodiversity and productivity. Monogeneans have been studied for more than 120 years, and 58 nominal species have been recorded in the Seto inland Sea. This study provided DNA information on five species of Benedenia sensu lato (Capsalidae) from marine fishes from the sea, and one of them, Benedenia kobudai n. sp., is described from Semicossyphus reticulatus (Perciformes: Labridae). This new species differs from the other congeners by the hooded appearance between the anterior attachment organs, the morphology of the penis, the absence of the lobe near the vaginal pore and the common genital pore, the position of the vaginal pore, the germarium lying near the slightly hexagonal testes, the morphology of the haptor, and the shape and position of the hamuli. Phylogenetic analysis showed B. kobudai n. sp. in a separate clade from the other Benedenia species, B. epinepheli, B. hoshinai, B. sekii, and B. seriolae collected from the sea. Each of the newly provided DNA sequences (28S rDNA, ITS1-5.8S-ITS2, cox1) of the above four species are based on specimens obtained from the type hosts and/or type localities and are considered important for future taxonomic re-examination and confirmation of the reliability of the registered sequences. Furthermore, these four species are important causes of fish diseases in aquaculture, and it is expected that information on the distribution, host range, and occurrence of fish diseases for each capsalid secured by molecular identification will be accumulated. The Life Science Identifier (LSID): urn:lsid:zoobank.org:pub:26C15D17-CFD1-450D-9FCE-EFFF692D2133.

Kannaphallus leptosomus n. sp. (Monogenea: Heteraxinidae: Cemocotylinae) parasitizing Scyris indica (Carangiformes: Carangidae) from Malaysia.

A new monogenean species, Kannaphallus leptosomus n. sp., from the gills of the diamond trevally, Scyris indica Rüppell, caught off Terengganu, Peninsular Malaysia is described with molecular data. The new species differs from other species of the genus by the morphology of the largest clamp, the presence of a penis gun-associated needle, the unarmed genital atrium size, and the presence of two independent vaginal tubes. Previous records of Kannaphallus species were compiled, and four nominal species including one species incertae sedis (K. virilis Unnithan, 1957; K. lateriporis Mamaev, 1988; K. leptosomus n. sp.; and K. mochimae Fuentes Zambrano, 1998 incertae sedis) and two undescribed species recorded as invalid names were listed. Cemocotylelloides carangis Ramalingam, 1969 was considered a junior objective synonym of K. univaginalis Ramalingam, 1960; this species was treated as Cemocotylelloides univaginalis n. comb. In addition, Unnithan's materials including type specimens of K. virilis could not be found in specimen repositories in India, and it appears that the specimens were probably not deposited in any institution or have been subsequently lost. Based on the phylogenetic analysis of 28S rDNA sequences, Heteraxinidae was broadly divided into two clades, and Heteraxininae and Cemocotylinae were shown as polyphyletic groups, respectively.

Exploring evolutionary trends within the Pennellidae (Copepoda: Siphonostomatoida) using molecular data.

The family Pennellidae comprises ecto- and mesoparasitic copepods on marine fishes. Although a preliminary scheme of phylogenetic relationships of pennellids based on morphological characters exists, it is difficult to objectively define character states because of their highly modified bodies and reduced appendages. This molecule-based study analysed phylogenetic relationships among seven genera and 12 species of pennellids, using 18S and 28S ribosomal DNA sequences in order to infer evolutionary trends within the family. Our molecular analysis recovered three clades (Clade-I, Peniculus; Clade-II, Haemobaphes-Lernaeocera-Phrixocephalus-Exopenna-Lernaeenicus radiatus; and Clade-III, Pennella-Lernaeenicus spp.). This result was congruent with some of the morphology-based phylogenetic relationships previously proposed but did not support a sister group comprising Exopenna, Phrixocephalus and Pennella. The second and third offshoots after the divergence of Clade-I species are characterized by reduced body tagmosis and changes in lifestyle from ectoparasites to mesoparasites. In some gill parasites of Clade-II, their sigmoid-shaped bodies and coiled egg strings have likely evolved in adaptation to the limited available space within the gill cavities of the hosts. Phrixocephalus is an eye parasite in Clade-II, which also has coiled egg strings, may have descended from an ancestral gill parasite. All species of Clade-III are characterized by the possession of a head region with processes deeply embedded into the host tissues and functioning as an anchor.

Capsalids (Platyhelminthes: Monogenea) from marine fishes off Okinawa in Japan with the proposal of two new genera.

Molecular studies of the Capsalidae suggested that the genus Benedenia is polyphyletic, but a taxonomic organization of the genus that reflects molecular data has not yet been proposed. As a result of molecular analysis (28S rDNA, ITS1-5.8S-ITS2, and cox1 data) including specimens of Benedeniinae newly obtained from Okinawa-jima Island in Japan, two new genera and the revival of Tareenia independent to the genus Benedenia are proposed. Gracilobenedenia n. gen. is distinguished from the other genera of Benedeniinae based on morphological characteristics. This new genus comprises 6 species: G. lutjani n. comb. (type species), G. anticavaginata n. comb., G. rohdei n. comb., G. beverleyburtonae n. comb., G. kuremibai n. gen., n. sp., and G. hichi n. gen., n. sp. Armatobenedenia n. gen. is a monotypic genus for A. armata n. comb. The present molecular phylogenetic analysis showed the independence of Tareenia, and it can be morphologically separated from the other benedeniines. Four species including two new species obtained from Okinawa-jima Island are reported: G. kuremibai n. sp., G. hichi n. sp., G. lutjani n. comb., and Metabenedeniella parva. Furthermore, in the species identification and phylogenetic analysis of capsalids, the usefulness of not only the 28S rDNA but also ITS and the cox1 regions was suggested. These genes were evaluated the efficacy of those regions in DNA barcoding, and the ITS and cox1 regions shown to be useful for DNA barcoding in capsalids compared to the 28S rDNA sequence.

A new monogenean species, Gyrodactylus ajime n. sp. (Gyrodactylidae), parasitic on Niwaella delicata (Niwa), an endemic loach of Japan.

A new gyrodactylid species, Gyrodactylus ajime n. sp., is described from the skin and fins of an endemic and commercially important loach Niwaella delicata (Niwa) (Cypriniformes: Cobitoidea: Cobitidae), from the upper reach of the River Yura in Ashiu, Kyoto Prefecture, Japan with scanning electron microscopy observations and molecular data. This species can be distinguished from congenerics by characteristics of the sickle of the marginal hook: the sickle proper is composed of two straight sections and a curved section; its short point extends beyond the limit of the toe and is directed downwards; and the upper corner of heel angular is slightly raised. There are 31 species and subspecies of native loaches (Cobitoidea) known from Japan, of which 25 are red-listed nationally, and two are commercially important. I reviewed all reports of monogeneans from Japanese loaches, and found that only five fish species have been recorded as hosts of these parasites. This suggests that the parasite fauna of these fishes is poorly described. It is urgent to thoroughly describe the monogenean parasites of loaches in Japan as some of the parasite species may be threatened with co-extinction because their hosts are threatened, and to understand any negative impacts on commercially important fish species.

Lamellodiscus (Monogenea: Diplectanidae) species parasitic on Japanese Acanthopagrus Peters, with proposals of L. chin n. sp. infecting A. sivicolus Akazaki and L. egusai nom. nov. for L. japonicus Ogawa & Egusa, 1978, a junior homonym of L. japonicus Pillai & Pillai, 1974.

Lamellodiscus chin n. sp. (Monogenea: Diplectanidae) was described from Acanthopagrus sivicolus Akazaki (Perciformes: Sparidae) in Okinawa-jima Island, Ryukyu Islands based on morphological and molecular data. This new species resembles L. spari and L. elegans in morphologically but differs by its accessory piece curving and widening toward the tip. Three species of Lamellodiscus (L. japonicus Ogawa & Egusa, 1978, L. takitai Ogawa & Egusa, 1978, and L. spari Zhukov, 1970) were recorded from A. schlegelii (Bleeker), and L. japonicus was collected from A. latus (Houttuyn) in the Seto Inland Sea, Japan. I herein propose Lamellodiscus egusai nom. nov. for L. japonicus which is a junior primary homonym of L. japonicus Pillai & Pillai, 1974. Based on the type specimens and newly collected specimens from wild hosts, the type localities of L. japonicus (= L. egusai nom. nov.) and L. takitai are discussed. In addition, a list of nominal species of Japanese diplectanids is provided.

Description of Raphidascaris (Ichthyascaris) multipapillata sp. nov., Redescription of Hysterothylacium simile Li et al., 2013 and New Records of Some Other Ascaridoid and Seuratoid Nematodes from Marine Fishes in Japan.

PURPOSE: Many nematode species parasitizing marine fishes were reported from Japanese waters. However, considering the wealth of fish species in this zoogeographically interesting region and the host specificity of nematodes, the number of hitherto recorded fish nematodes probably represents only a very small part of the potential Japanese fauna of these organisms. Therefore, new data are needed to recognise the species composition of these parasites in this region. METHODS: Helminthological examinations of some marine fishes from off Japan, carried out in the years 2005-2017, revealed one new and five insufficiently known species of ascaridoid and seuratoid nematodes. These were studied with the use of light and scanning electron microscopy. RESULTS: All six nematode species recorded are described: Anisakidae: Raphidascaris (Ichthyascaris) multipapillata sp. nov. (male and females) from the intestine of Labracoglossa argenteiventris Peters (Kyphosidae) in the Sea of Japan, Raphidascaris (Ichthyascaris) sp. (third-stage larvae) probably from the digestive tract of Seriola dumerili (Risso) and S. rivoliana Valenciennes (both Carangidae) in the western North Pacific Ocean off Ishigaki-jima Island, Okinawa Prefecture, Hysterothylacium simile Li et al., 2013 (males and females) from the stomach of Lateolabrax japonicus (Cuvier) (Lateolabracidae) in the Sea of Japan, Hysterothylacium sp. 1 (female) from the pyloric caeca of Jaydia lineata (Temminck et Schlegel) (Apogonidae) in the Seto Inland Sea, Hysterothylacium sp. 2 (third- and fourth-stage larvae) from the intestine and mesentery of Etelis coruscans Valenciennes (Lutjanidae) and Pseudorhombus pentophthalmus Günther (Paralichthyidae) in the western North Pacific Ocean off Ishigaki-jima Island, Okinawa Prefecture and the Seto Inland Sea, respectively; and Cucullanidae: Cucullanus sp. (female) from the intestine of Semicossyphus reticulatus (Valenciennes) (Labridae) in the Seto Inland Sea. Raphidascaris (I.) multipapillata sp. n. differs from congeners mainly in the high number (79) of pairs of caudal papillae, spicules 402 µm long and in the structure of the male and female tail tips. Hysterothylacium simile is redescribed, being recorded from off Japan for the first time. CONCLUSIONS: In addition to the discovery of the new nematode species R. (I.) multipapillata sp. nov. and a redescription of H. simile providing some new morphological data of this parasite, the findings of all other species represent new host and geographical records. The present study extends the knowledge of the species composition and host-parasite relationships of nematodes parasitizing marine fishes.

Two species of Dioncopseudobenedenia Yamaguti, 1965 (Monogenea: Capsalidae) from Naso unicornis (Forsskål) (Acanthuridae) and Coryphaena hippurus Linnaeus (Coryphaenidae) in western Japan, with a description of D. elongata n. sp. from N. unicornis.

Three species of Dioncopseudobenedenia Yamaguti, 1965 (Monogenea: Capsalidae: Benedeniinae) have been described, all found parasitising Naso spp. (Acanthuridae) and Siganus lineatus (Siganidae), in Hawaii, the Great Barrier Reef, and New Caledonia in the Pacific. In this paper, D. elongata n. sp. is described, found parasitising the gills of N. unicornis (Forsskål) caught off Okinawa-jima Island. Dioncopseudobenedenia kala Yamaguti, 1965 is also reported, found parasitising the gills of N. unicornis, and those of a new host, the common dolphinfish Coryphaena hippurus Linnaeus (Coryphaenidae), off Okinawa and Kochi prefectures, Japan. The new species differed from known species in both nuclear (28S rDNA and ITS1-5.8S-ITS2) and mitochondrial DNA (cox1) sequences. Morphologically, the new species differed from other species of Dioncopseudobenedenia in possessing a longer accessory sclerite and a thick, short penis. No species of Dioncopseudobenedenia have been detected during past examinations of C. hippurus; this instance was probably an accidental infection. A key for identification of the species of Dioncopseudobenedenia is also provided herein.

Taxonomic revision of Microcotyle caudata Goto, 1894 parasitic on gills of sebastids (Scorpaeniformes: Sebastidae), with a description of Microcotyle kasago n. sp. (Monogenea: Microcotylidae) from off Japan.

Two species of microcotylid monogeneans, Microcotyle caudata Goto, 1894 and Microcotyle sebastisci Yamaguti, 1958, have been reported from fishes of the Sebastes inermis species complex and Sebastiscus marmoratus (Cuvier) (Scorpaeniformes: Sebastidae). So far, these parasite species have been distinguished by the size of the eggs and the number of testes, but based on morphological evidence including re-examination of the type-specimens and topotypes and molecular analysis, we consider M. sebastisci to be a junior synonym of M. caudata. As a result, M. caudata exhibits a wide host range, seven species from three genera and two families. A new species, Microcotyle kasago n. sp., is described based on material from S. marmoratus and differentiated from other congeners by means of morphological and molecular analysis.

Discovery of the fish host of the 'planktonic' caligid Caligus undulatus Shen & Li, 1959 (Crustacea: Copepoda: Siphonostomatoida).

The siphonostomatoid copepod Caligus undulatus Shen & Li, 1959 has been widely reported from plankton samples obtained from neritic and oceanic waters off coasts of the Indo-West Pacific and Atlantic Oceans. Until now, its fish host has remained unknown. This copepod belongs to an intriguing group of congeners that, despite being part of a chiefly parasitic group, are consistently found as zooplankters. Quite unexpectedly, in October 2019, a fish host of C. undulatus was discovered in the Seto Inland Sea, Japan-namely, the Japanese sardinella Sardinella zunasi (Bleeker, 1854). Both juvenile (chalimus) and adult individuals of this caligid were observed as parasites of the fish host. The discovery suggests that the species has an alternative life cycle as previously proposed for other purportedly 'planktonic' congeners and might frequently switch hosts during the adult stage. Thus, the C. undulatus group is newly proposed as a species group in the genus, in which five species are known as planktonic. Some hypotheses on the modified life cycle of caligids also briefly discussed.

Gobioecetes longibasais n. sp. (Monogenea: Dactylogyridae) from Rhinogobius similis Gill (Perciformes: Gobiidae) from Okinawa-jima Island, the Ryukyu Archipelago, southern Japan, with a new host record for Gobioecetes biwaensis Ogawa & Itoh, 2017.

Gobioecetes longibasis n. sp. (Monogenea: Dactylogyridae) from the gills of the freshwater goby Rhinogobius similis Gill (Perciformes: Gobiidae) in the River Teima, Okinawa-jima Island, the Ryukyu Archipelago, southern Japan, is described. The new species is distinguished from two congeneric species of Gobioecetes Ogawa & Itoh, 2017, G. rhinogobius (Ling, 1973) and G. biwaensis Ogawa & Itoh, 2017, by having longer ventral hamuli, longer and wider internal process of the dorsal hamuli, and the ratio of dorsal hamulus length to base length. This new species is host-specific to R. similis and considered to be endemic to Okinawa-jima Island or the Ryukyu Archipelago. We also report Rhinogobius sp. OM from a tributary of Lake Biwa, Shiga Prefecture, central Japan, as a new host of G. biwaensis.

New records of philometrids (Nematoda: Philometridae) from marine fishes off Japan, including description of Philometra kidakoi sp. n. and Congerinema japonicum gen. et sp. n.

Occasional examinations of some marine fishes in Japan revealed, in addition to other parasites, the following eight species of philometrid nematodes (Philometridae) (all females only): Philometra kidakoi sp. n. from the ovary of Gymnothorax kidako (Temminck et Schlegel) (Muraenidae); Philometra pinnicola (Yamaguti, 1935) from the operculum of Epinephelus akaara (Temminck et Schlegel) (Serranidae); Philometra sebastisci Yamaguti, 1941 from the ovary of Sebastes cheni Barsukov (Scorpaenidae) (new host); Philometra madai Quiazon, Yoshinaga et Ogawa, 2008 from the ovary of Acanthopagrus schlegelii (Bleeker) (Sparidae) (new host); Philometra isaki Quiazon, Yoshinaga et Ogawa, 2008 from the ovary of Parapristipoma trilineatum (Thunberg) (Haemulidae); Philometra sp. from the ovary of Synanceia verrucosa Bloch et Schneider (Synanceiidae); Congerinema japonicum gen. et sp. n. from the subcutaneous tissue of Conger myriaster (Brevoort) (Congridae); and Clavinema mariae (Layman, 1930) from the operculum of Acentrogobius pflaumii (Bleeker) (Gobiidae). Specimens of all species are described based on light and scanning electron microscopical examinations. Philometra kidakoi sp. n. is the first gonad-infecting philometrid from the Muraenidae. The new monotypic genus Congerinema gen. n. is characterised by the unique net-like cuticular ornamentation on the female body. Clavinema mariae is considered to be a complex of several cryptic species and a need of the discovery of conspecific males is stressed (this also concerns other philometrid species with unknown males). At present, the fauna of philometrid nematodes parasitising marine fishes in Japanese waters is represented by 22 nominal species belonging to four genera.

A new genus for Diplectanum setosum Nagibina, 1976 (Monogenea: Dipletanidae), a parasite of Psammoperca waigiensis (Cuvier) (Perciformes: Latidae) from Okinawa-jima Island, Japan.

The diplectanid monogenean Diplectanum setosum Nagibina, 1976 is redescribed based on newly collected specimens from Psammoperca waigiensis (Cuvier) (Perciformes: Latidae) from the Okinawa-jima Islands, Okinawa Prefecture, Japan, and transferred to a new genus, Latiphagum n. g., herein proposed based on the results of the morphological and molecular analysis. This new genus is closely related with Pseudorhabdosynochus Yamaguti, 1958, Echinoplectanum Justine & Euzet, 2006, and Laticola Yang, Kritsky, Sun, Zhang, Shi, & Agrawal, 2006, but distinguished from them by the male copulatory organ (MCO) of the new genus devoid of cirrus, the tube supported both sides by two plates with long bristles, and the presence of the prostatic reservoir in the expanded base of the MCO.

A new species of Benedenia Diesing, 1858 (Monogenea: Capsalidae) parasitic on Lethrinus haematopterus Temminck & Schlegel (Perciformes: Lethrinidae) from Japan.

A new species of capsalid monogenean, Benedenia armata n. sp., is described from Lethrinus haematopterus Temminck & Schlegel (Perciformes: Lethrinidae) from off Danjo Islands, Nagasaki Prefecture, Japan. The new species differs from other species of Benedenia Diesing, 1858 in that the common genital atrium has spines and the vas deferens has two swellings. Lethrinus haematopterus has been considered as the type-host of Benedenia ishikawae (Goto, 1894) based on the local name 'Kuchibi-dai'. However, this name refers not only to L. haematopterus but also to L. nebulosus (Forsskål), and L. haematopterus examined in this study was not infected by B. ishikawae. Further study is required to determine the type-host of B. ishikawae and to redetermine the species of Benedenia that are parasitic on Lethrinus spp. in the type-locality of B. ishikawae (Hagi, Yamaguchi Prefecture, Japan).

A New Species of Lagochondria (Crustacea: Copepoda) Parasitic on Callionymid Fish: First Record of Precopulatory Mate Guarding in Fish-Parasitic Cyclopoid Copepods, and of the Occurrence of the Genus in the North Pacific.

A new species of the genus Lagochondria of the parasitic cyclopoid family Chondracanthidae is described from the gill cavity of the callionymid Repomucenus virgis (Jordan and Fowler, 1903) collected from off Kii Peninsula, Japan. This is the first record of the occurrence of the genus from the North Pacific, and is only the second species in the genus. The female of the new species is easily distinguished from that of the Australian type species L. nana Ho and Dojiri, 1988 by having a squared trunk lacking paired posterior processes, and by the very short neck. In the male, the new species can be differentiated from the type species by having three inner setae on the caudal ramus, and by the distal segment of the antennule having a setal formula of 4, 3, 7+ ae. An adult female was accompanied by an attached adult male, whereas fourth and fifth copepodid females each carried a fifth and a fourth attached copepodid male, respectively. This is the first record of precopulatory mate guarding in a cyclopoid family parasitic on fish hosts, and of mate guarding between late copepodids of both sexes. The zoogeography of the genus and its relatives with an atrophied tip on the antenna is also discussed.

Choanotrema nom. nov. (Trematoda: Opecoelidae), a new replacement name for Choanostoma Yamaguti, 1934, a junior homonym of Choanostoma Wang, 1930 (Ciliophora: Haptorida: Didiniidae).

Choanostoma Yamaguti, 1934 was established for Choanostoma plectorhynchi Yamaguti, 1934 (Trematoda: Opecoelidae). The generic name Choanostoma, however, is a junior homonym of Choanostoma Wang, 1930 (Ciliophora: Haptorida: Didiniidae), and we propose a new replacement name, Choanotrema nom. nov.

Gyrodactylus medaka n. sp. (Monogenea: Gyrodactylidae) parasitic on wild and laboratory-reared medaka Oryzias latipes (Beloniformes: Adrianichthyidae) in Japan.

Gyrodactylus medaka n. sp. (Monogenea: Gyrodactylidae) is described from the skin, fins, and gills of medaka Oryzias latipes (Beloniformes: Adrianichthyidae) from Japan. This new species was collected from wild medaka in Hiroshima, Aichi, Saga, and Kumamoto prefectures, and laboratory-reared medaka in Chiba and Aichi prefectures. The small marginal hook sickle (≤4 µm) and the length of the marginal hook of the new species are the diagnostic morphological characters differentiated from other gyrodactylids reported from Asia. The pairwise sequence divergences for the interspecific variation in ITS regions and the phylogenetic analysis suggest that the populations of G. medaka n. sp. may have a similar genetic variation as the medaka populations in Japan. Gyrodactylus medaka n. sp. and Dactylogyrus oryziasi (Monogenea: Dactylogyridae) can maintain their populations in laboratory aquaria using medaka as their hosts, and these monogeneans and medaka have the potential as experimental model animals for clarifying various aspects of their host-parasite relationships. In addition, we report the composition of modified ammonium picrate-glycerin (APG) and show it is advantageous for monogenean taxonomy.