From commensalism to parasitism within a genus-level clade of barnacles.

Understanding how animals evolve to become parasites is key to unravelling how biodiversity is generated as a whole, as parasites could account for half of all species richness. Two significant impediments to this are that parasites fossilize poorly and that they retain few clear shared morphological features with non-parasitic relatives. Barnacles include some of the most astonishingly adapted parasites with the adult body reduced to just a network of tubes plus an external reproductive body, but how they originated from the sessile, filter-feeding form is still a mystery. Here, we present compelling molecular evidence that the exceedingly rare scale-worm parasite barnacle Rhizolepas is positioned within a clade comprising species currently assigned to Octolasmis, a genus exclusively commensal with at least six different phyla of animals. Our results imply that species in this genus-level clade represent an array of species at various transitional stages from free-living to parasitic in terms of plate reduction and host-parasite intimacy. Diverging only about 19.15 million years ago, the route to parasitism in Rhizolepas was associated with rapid modifications in anatomy, a pattern that was likely true for many other parasitic lineages.

Two new species of the genus Anilocra Leach, 1818 (Isopoda: Cymothoidae) parasitic on reef fishes from the western Pacific.

Anilocra harazakii sp. nov. and Anilocra boucheti sp. nov. are described from specimens collected from Pterocaesio marri (Caesionidae) in the northern Ryukyu Islands, Japan and Myripristis kuntee (Holocentridae) off Madang, Papua New Guinea, respectively. Anilocra harazakii sp. nov. is characterized by the combination of the following characters in the female: the elongate narrow body dorsally vaulted; the pleonite 1 concealed by the pereonite 7; the uropod extending that of the angled pleotelson, and its endopod longer than the exopod; and the dactyli of only pereopods 2 and 3 with one nodule on anterior margins. Anilocra boucheti sp. nov. is characterized by the following: body with convex lateral margins; almost part of the pleonite 1 not concealed by the pereonite 7; pleonite 5 with posterolateral acute angle strongly produced; coxa 3 clearly smaller than coxae 1 and 2; the uropod not extending past the posterior margin of the pleotelson with the tip of one of the rami not exceeding the other; and the dactyli of pereopods 1-4 without nodules. Furthermore, the coloration, i.e., the orange body with black margins, of A. boucheti sp. nov. is unique. Bayesian inference tree using partial mitochondrial cytochrome c oxidase subunit I (COI) genes supported the monophyletic clade composed of the members of the genus Anilocra including the two new species. Since the wounds caused by A. harazakii sp. nov. are often hemorrhagic, the isopod might have severe negative effects on the host. LSID urn:lsid:zoobank.org:pub:1C426C15-6FB7-49E4-AD49-02BE532D9ABB.

Ceratosomicola oki n. sp., a New Species of Copepod (Cyclopoida: Splanchnotrophidae) Parasitic on the Chromodoridid Nudibranch Glossodoris misakinosibogae Baba, 1988 Off the Oki Islands, Japan, with Microanatomical Observation Using Micro-CT.

A new species of the family Splanchnotrophidae Norman and Scott, 1906 (Cyclopoida) is described based on both sexes collected from off the Oki Islands, the Sea of Japan. Specimens of both sexes of Ceratosomicola oki n. sp. were found in the body cavities of Glossodoris misakinosibogae Baba, 1988 (Nudibranchia: Chromodorididae). The copepod is characterized by the following female characters: the cephalosome with a pair of dorsolateral horn-like processes; the prosome with hemispherical posterolateral lobes on the middle region. Non-destructive, micro-computed tomography (micro-CT) imaging performed on a single specimen of the nudibranch revealed a heavy infection by a total 17 specimens of C. oki n. sp. Almost all individuals of the copepod were attached on the surface of the middle to posterior parts of the visceral sac, forming a dense cluster. The four females bearing developed lateral processes on the prosome faced the anterior end of the visceral sac and positioned the posterior tip of the body under the secondary gills of the host. The males fitted in the gaps between the females' bodies. Further, the distribution and shape of the reproductive organs of both sexes were partially clarified by micro-CT imaging.

Choreftria shiranui, a new genus and species of cyclopoid copepod (Crustacea: Copepoda) associated with the worm goby from southern Japan, with the proposal of a new family.

A new genus and species of cyclopoid copepod, Choreftria shiranui n. g., n. sp. (Crustacea: Copepoda) is described based on an adult female found from the worm goby, Taenioides snyderi Jordan & Hubbs (Actinopterygii: Perciformes: Gobiidae), from mud flats in the Yatsushiro Sea, southern Japan. The new genus is characterized by bearing the following characters in the female: body distinctly segmented cyclopiform with 4-segmented prosome and 6-segmented urosome; genital somite clearly separated from first abdominal somite; antennule 7-segmented; antenna 4-segmented with one fused serrated claw and long claw on second endopodal segment; mandible reduced with one serrated blade; maxillule rod-like with one element; maxilla 2-segmented with recurved terminal claw; maxilliped 2-segmented; legs 1 to 4 biramous with 3-segmented rami. Since the copepod is not attributable to any of the known cyclopoid families, a new family, Choreftriidae n. fam. is established to accommodate Choreftria n. g. LSID urn:lsid:zoobank.org:pub:C1FB9F60-9871-4D4B-A1BF-3202BA24189F.

Three species of copepods parasitic on the blue mackerel Scomber australasicus Cuvier (Actinopterygii: Perciformes: Scombridae) from southern Japan, with description of a new species Colobomatus itoui n. sp. (Cyclopoida: Philichthyidae).

The blue mackerel Scomber australasicus is one of the major commercial fishes consumed in southern Japan. Three species of parasitic copepods were collected from S. australasicus in the East China Sea off the west coast of Kyushu Island, southern Japan. These copepods are each characterized based on the females: Pumiliopes scombri (Bomolochidae) differs from its congeners by the presence of fine ventral spinules on legs 2 to 4; Colobomatus itoui n. sp. (Philichthyidae) is characterized by having the cephalosome with a pair of dorsal hemispherical cephalic protrusions but without an apical cephalic process and the anal somite with a pair of posterolateral protrusions with a smooth tip; and Caligus kanagurta (Caligidae) is distinguishable from its congeners accommodated in the Caligus diaphanus-group by bearing an atypical bulged leg 4 with long protruded pectens. The collection of C. kanagurta in Japanese waters represents its new country record. Parasitic copepods reported from S. australasicus and its related species S. japonicus from the western Pacific Ocean are tabulated.LSID urn:lsid:zoobank.org:pub:382569AD-5188-4443-AAA8-1C2DB4FE2689.

Distribution and Genetic Divergence of Deep-Sea Hydrothermal Vent Copepods (Dirivultidae: Siphonostomatoida: Copepoda) in the Northwestern Pacific.

Copepods in the family Dirivultidae are one of the most successful meiofauna in deep-sea hydrothermal vent fields and are abundant near venting fluid. Although vents are spatially limited ocean habitats, they are distributed widely in the Atlantic, Pacific, and Indian Oceans. However, knowledge of dirivultid biogeography and phylogeography remains limited, especially in the northwestern Pacific. Here, we obtained partial mitochondrial COI gene sequences of three dirivultids from the northwestern Pacific-Stygiopontius senokuchiae and an unidentified Chasmatopontius species from vent fields in the Izu-Bonin Arc and Stygiopontius senckenbergi associated with the squat lobster Shinkaia crosnieri in the Okinawa Trough-and analyzed them in comparison with existing data. The among-species sequence diversity exceeded 80 out of 560 bp (14% or 0.166 in Kimura 2-parameter distance), whereas the within-species diversity was less than 10 bp (2% or 0.018 in Kimura 2-parameter distance), with no genetic saturation. Each species formed a monophyletic clade and the genetic region targeted is deemed reliable for identifying species and populations for these copepods. Among the three genera targeted, only Chasmatopontius formed a monophyletic cluster, while Aphotopontius and Stygiopontius did not. Species delimitation analyses suggested the existence of cryptic species in Chasmatopontius. Subdivision among local populations was observed in Aphotopontius, but not in Stygiopontius in the same distribution, implying potential differences in dispersal ability among different genera of dirivultids. Further sampling is required, to fill the spatial gaps to elucidate the biogeography and evolution of dirivultids in the global deep ocean.

New replacement name for a homonym in Lepeophtheirus (Crustacea: Copepoda: Caligidae).

Markevich (1940) established Pseudolepeophtheirus Markevich, 1940 for Pseudolepeophtheirus longicauda Markevich, 1940 based on copepods collected from the pleuronectid fish Platichthys stellatus (Pallas, 1787). Dojiri Ho (2013) synonymized the genus and the species with Lepeophtheirus Nordmann, 1832 and Lepeophtheirus parvicruris Fraser, 1920, respectively. Later, Homma et al. (2020) resurrected Markevich's species as a member of Lepeophtheirus, i.e., as L. longicauda (Markevich, 1940). The last component of the names of both genera is 'phtheirus' (transliterated from the Greek φθειρ; Nordmann 1832: 30), a masculine noun, and thus under Article 30.1.2 of the International Code of Zoological Nomenclature (hereinafter, Code; International Commission on Zoological Nomenclature 1999), both generic names are also masculine. The species-group name longicauda might be regarded as either a noun in apposition or as an adjective in the feminine gender, and Markevich (1940) did not specify his intention in this regard. Bearing in mind that 'cauda', meaning 'tail', actually is a feminine Latin noun and that Markevich did not change the final '-a' to '-us' to match the masculine gender of the genus, we deem that longicauda Markevich, 1940 is a noun in apposition, a position supported by Article 31.2.2 of the Code.

Integrative taxonomy of Pseudolepeophtheirus longicauda (Crustacea: Copepoda: Caligidae) parasitic on Platichthys stellatus (Actinopterygii: Pleuronectidae).

Based on specimens from the gill cavities of one Platichthys stellatus individual collected in the Sea of Japan, we investigated the taxonomic status of the enigmatic caligid genus Pseudolepeophtheirus and its type species, Pseudolepeophtheirus longicauda. In a maximum likelihood (ML) tree based on 18S rRNA gene sequences, the sequence from our sample was nested in a well-supported Lepeophtheirus clade, along with the type species, confirming that Pseudolepeophtheirus should be considered a junior synonym of Lepeophtheirus; our morphological data support this synonymy. Although a previous study had synonymized Pseudolepeophtheirus longicauda with Lepeophtheirus parvicruris, we found that the former differs morphologically from the latter in having a short leg-4 exopod, with the articulation between the first and second segments not evident (the shape of the posterior striated membrane on the leg-2 intercoxal sclerite also differs between two species), and detected slight differences in 18S rRNA sequences between two taxa. We thus concluded that this synonymy is invalid, and reinstate Lepeophtheirus longicauda as a valid species. A ML analysis of COI sequences from Pl. stellatus (the host fish for both L. longicauda and L. parvicruris) showed the host species to comprise distinct northwestern- and northeastern-Pacific clades. Lepeophtheirus longicauda is distributed in the northwestern Pacific and L. parvicruris in the northeastern Pacific, indicating co-divergence of the two copepod species with the host lineages.

Two new species of Panaietis (Copepoda: Cyclopoida: Anthessiidae) associated with vetigastropods (Gastropoda) in coastal waters of southern Japan.

Two new species of the genus Panaietis (Copepoda: Cyclopoida: Anthessiidae) inhabiting the inside of the mouth cavities of marine snails are described from shallow waters of southern Japan. Panaietis bobocephala sp. nov. collected from the small abalone, Haliotis asinina (Vetigastropoda: Lepetellida: Haliotidae), is mainly characterized by the well-developed posterolateral corners of tergite on first pediger, the pointed spines on legs 1 to 5, the maxilla with two teeth, and the leg armature formula. Panaietis flavellata sp. nov. from Angaria neglecta (Vetigastropoda: Trochida: Angariidae) is characterized by the combination of following: leg 5 is situated on ventral side of the fifth pediger, inner margin of the second segment of antenna greatly protruded, and the leg armature formula.

A new dirivultid copepod (Siphonostomatoida) from hydrothermal vent fields of the Izu-Bonin Arc in the North Pacific Ocean.

A new species of dirivultid copepod (Siphonostomatoida) is described from hydrothermal vents in a volcanic seamount in Izu-Bonin Arc, western part of North Pacific Ocean. The copepod was collected during the research cruise NT13-09 using the R/V Natsushima with the ROV Hyper-Dolphin in April 2013. The type series of the new species was collected from the populations of Paralvinella spp. (Annelida: Alvinellidae) on an active vent chimney at the depth of 795 m. Stygiopontius senokuchiae n. sp. is most closely related to S. teres Humes, 1996 but clearly distinguished from the latter species by the possession of the following characters: the basis of leg 1 with an attenuated inner process; the genital double somite with a conical process lateral to the genital opening; and caudal rami without distal process. The findings of the copepod in the present study represents the first record of nominal species of the Dirivultidae from Japanese waters and a record of the shallowest depth of the genus. A key to species of the genus Stygiopontius from Western Pacific is provided.

Two new species of Sagum Wilson, 1913 (Copepoda: Siphonostomatoida: Lernanthropidae) parasitic on reef fishes off the Ryukyu Islands.

Two new species of parasitic copepods, Sagum gurukun n. sp. and S. bitaro n. sp. (Siphonostomatoida: Lernanthropidae), are described based on specimens collected from the gill filaments of the double-lined fusilier Pterocaesio digramma (Bleeker) (Actinopterygii: Perciformes: Caesionidae) and the five-lined snapper Lutjanus quinquelineatus (Bloch) (Actinopterygii: Perciformes: Lutjanidae), respectively, caught off Iriomote-jima Island, the Ryukyu Islands, East China Sea, Japan. The findings bring the number of species of Sagum to 14. The two new species are similar in the morphology of the head and the legs 3 and 4 to the three congeners, S. folium Ho, Liu & Liu, 2011, S. paracaesionis Izawa, 2014 and S. vietnamiensis Kazachenko, Kovaleva, Nguyen & Ngo, 2017. Sagum gurukun n. sp. is differentiated from the three congeners by the proportions of the caudal rami, the absence of leg 5, and the shape of the legs 1 and 2. Sagum bitaro n. sp. differs from the three congeners and S. gurukun n. sp. by the presence of the conical leg 5 armed with an apical seta. A key to the species of the genus Sagum, based on the available information on female morphology in previous publications and the present study, is provided. To date, a total of 19 species of lernanthropid copepods considered valid are known in Japanese waters.

Lomanoticola nishiharai n. sp., a New Species of Copepod Parasitic on the Facelinid Nudibranch, Sakuraeolis enosimensis (Baba, 1930), from the Seto Inland Sea, Western Japan, Including Histological Observations of the Female Lateral Body Process.

Splanchnotrophidae Norman and Scott, 1906 is a family of parasitic copepods that infest nudibranchian and sacoglossan sea slugs. In this study, a new species of splanchnotrophid copepod, Lomanoticola nishiharai n. sp., is described based on specimens of both sexes collected from the facelinid nudibranch, Sakuraeolis enosimensis (Baba, 1930), in the Seto Inland Sea off Hiroshima, central Japan. It represents the third species of Lomanoticola Scott and Scott, 1895 and is characterized by the following female characters: the cephalosome distinctly protruded; the second and third lateral processes on the body originated from same bases; the caudal rami bears a seta V which almost same as long as the rami. Ultrastructural observations revealed that the cuticular surface of the lateral process on the female body is covered with numerous protuberances that may have protective functions against the cellular immune system of the host.

Copepods (Cyclopoida) associated with top shells (Vestigastropoda: Trochoidea: Tegulidae) from coastal waters in southern Japan, with descriptions of three new species.

Four species of copepods are described based on specimens of both sexes from tegulid top shells (Vestigastropoda) caught from coastal waters of southern Japan. Three species, including two undescribed and one known of the genus Panaietis (Copepoda: Cyclopoida: Anthessiidae) were found in the pharynx and esophagus of gastropods. Panaietis incamerata Stebbing, 1900, P. doraconis n. sp., and P. satsuma n. sp. are distinguished from its congeners by the dorsal plates on the first pedigerous somite, the genital somite, the shape of the spines on legs, the number of setae on legs 1 and 2, and the position and shape of leg 5. Pseudanthessius imo n. sp. (Cyclopoida: Pseudanthessiidae) was found in the mantle cavity of the host. This copepod differs from its congeners in the proportions of the caudal ramus, the armature and proportion of the antenna, the armature of the exopod and general shape of the endopod of leg 4, and the presence of a post-rostral process.

A review of the Taeniacanthus balistae species group (Crustacea: Copepoda: Taeniacanthidae), with descriptions of two new species.

The Taeniacanthus balistae species group is characterized by two displaced elements on an outwardly curved and elongated terminal exopodal segment of leg 4. Members of this group parasitize tetraodontiform fishes. The group is reviewed herein based on both new material collected from tetraodontiform fishes and re-examination of voucher specimens housed at the Smithsonian Institution, U.S.A. Five species are considered valid in this group, including two new species described here, Taeniacanthus dojirii sp. nov. from diodontid hosts collected from the Indo-West Pacific and Taeniacanthus ryukyuensis sp. nov. from balistid hosts collected from the Ryukyu Islands, Japan. Taeniacanthus dojirii sp. nov. differs from other members of the group by having in the female stout spines on the terminal endopodal segment of legs 2 to 4 and on the exopod of leg 5, as well as highly reduced setae on the last two exopodal segments of leg 4. Taeniacanthus ryukyuensis sp. nov. differs from other members of the group by having in the female 16-18 incomplete rows of spinules on the anal somite, minute teeth on the straight terminal claw of the maxilliped and well-developed spinulated flanges on the rami of legs 2 to 4. Supplemental morphological observations, as well as new host and locality records for Taenicanthus balistae (Claus, 1864) and Taeniacanthus similis Dojiri & Cressey, 1987, are also provided.

Nippoparasitus unoashicola, a new genus and species of philoblennid copepod (Cyclopoida) parasitic on the Pacific sugar limpet, Patelloida saccharina (Linnaeus, 1758) (Patellogastropoda: Lottiidae) from the intertidal zone of eastern Japan.

Nippoparasitus unoashicola, a new genus and species of mesoparasitic copepod, is described based on specimens of both sexes collected from the mantle cavity of the Pacific sugar limpet, Patelloida saccharina (Linnaeus, 1758) (Patellogastropoda: Lottiidae), in the intertidal zone of the Uraga Channel (North Pacific Ocean), Japan. Nippoparasitus gen. nov. differs from other philoblennid genera by two unique characters: the labium is bloated and branched into multiple digitate lobes in female, and the antenna has three claw-like spines on the terminal segment. Nippoparasitus is probably closely related to Myzotheridion Laubier & Bouchet, 1976 with which it shares a series of processes on the terminal segment of the maxilla.

Systematic revision of the pennellid genus Creopelates Shiino, 1958 (Copepoda: Siphonostomatoida) and the proposal of a new genus.

The parasitic copepod Creopelates floridus Shiino, 1958 (Siphonostomatoida: Pennellidae) is redescribed based on postmetamorphic adult females in the collection of the Imperial Majesty of Japan deposited in the National Museum of Nature and Science, Tsukuba (NSMT), Japan. Five new species of pennellid copepods are described based on postmetamorphic adult females from marine actinopterygian fishes newly collected in littoral waters of Japan and the Philippines, in the western North Pacific. The copepods and their hosts are as follows: Creopelates hosinoi n. sp. from Bryaninops yongei (Davis & Cohen) (Perciformes: Gobiidae); C. shirakawai n. sp. from Diancistrus fuscus (Fowler) (Ophidiiformes: Bythitidae); C. lubangenesis n. sp. from Gobiodon rivulatus (Rüppell) (Perciformes: Gobiidae); Nagasawanus akinohama n. gen. et n. sp. from Trimma grammistes (Tomiyama) (Perciformes: Gobiidae); N. snufkini n. gen. et n. sp. from T. tevegae Cohen & Davis. The total number of valid species contained in the genus Creopelates is now five. Nagasawanus n. gen. is distinguishable from other pennellid genera by the following features: antennary processes and cephalic lobes rounded without branched fringes, neck region without processes, maxilla with claw-like terminal segment lacking spinules. Keys to the genera of Pennellidae and to the species of Creopelates and Nagasawanus n. gen. are also provided.

Checklist of the marine and estuarine fishes of Madang District, Papua New Guinea, western Pacific Ocean, with 820 new records.

A checklist of the marine and estuarine fishes of Madang District is presented, combining both previous and new records. After the recent PAPUA NIUGINI 2012 expedition, a total of 1337 species in 129 families have been recorded from the region. One species and one family is not native (Cichlidae: Oreochromis mossambicus), but has been introduced. The native fish fauna of Madang therefore consists of 1336 species in 128 families. The largest families are the Gobiidae, Labridae, Pomacentridae, Apogonidae, Serranidae, Blenniidae, Chaetodontidae, Syngnathidae and Muraenidae, Scorpaenidae and Lutjanidae, Myctophidae, Acanthuridae, Scaridae, Holocentridae, Carangidae, Pomacanthidae and Tetraodontidae, and Caesionidae. A total of 820 fish species (61.4 % of the total marine and estuarine fish fauna) are recorded from Madang for the first time. The fish fauna of Madang includes a total of 187 species of transitional waters and 1326 species in marine habitats. A total of 156 species of the marine or estuarine species also occurs in freshwater. Zoogeographically, 1271 species have a wide distribution range, most frequently a broad Indo-West Pacific distribution. Among the remaining species, only 8 are endemic to Madang District. Anthropogenic threats to the fish fauna and habitats of Madang District include extensive fishing in Madang Lagoon, sometimes with destructive fishing practices; the discharge of untreated sewage of human settlements, mining and industrial developments into the lagoon and nearby oceanic habitats; and destruction of mangrove habitats by extensive construction work on the shores. These anthropogenic threats may call for conservation and monitoring measures in the near future.

Histopathology of a mesoparasitic hatschekiid copepod in hospite: does Mihbaicola sakamakii (Copepoda: Siphonostomatoida: Hatschekiidae) fast within the host fish tissue?

Mihbaicola sakamakii is a mesoparasitic copepod that infests the branchiostegal membranes of groupers (Perciformes: Serranidae). In this study, we observed M. sakamakii within host tissue. Histologically, copepods were found enclosed inside a pouch composed of the thickened epidermis of the host, tightly encased on all sides by the host epidermal pouch wall. There were no host blood cells or other food resources in the pouch lumen. Since the host epidermis was intact and continuous, even in the vicinity of the oral region of the parasite, the copepod would not have access to the host blood in this state. However, the stomach (ampullary part of the mid gut) was filled with granular components, the majority of which were crystalloids that likely originated from fish erythrocyte hemoglobin. We supposed that the parasite drinks blood exuded from the lesion in the fish caused by copepod entry into the host tissue. Invasion of the parasite may elicit immune responses in the host, but there were no traces on the copepod of any cellular immune reactions, such as encapsulation. The array of minute protuberances on the copepod cuticle surface may be involved in avoidance of cell adhesion. After the lesion has healed, the copepod is enclosed in a tough epidermal pouch, in which it gradually digests the contents of its stomach and continues egg production.

Parasitic copepods from two species of commercial fishes collected off Iraq, with description of Hatschekia shari n. sp.

Two species of parasitic copepods, including one new species, are described based on specimens collected from off Basrah, Iraq (Arabian Gulf). Hatschekia shari n. sp. (Siphonostomatoida: Hatschekiidae) was found from the gill filaments of the spangled emperor Lethrinus nebulosus (Forsskål) (Perciformes: Lethrinidae). The new species is characterised by the following characters in the female: a rectangular cephalothorax with dorsal frame composed of two short and one long bifid longitudinal bars, connecting to one short and one long latitudinal bars; elongate, cylindrical trunk without posterolateral processes or lobes; absence of parabasal papillae; and antennae bearing middle segments without narrow median part and with terminal claws without basal conical processes. Bactrochondria formosana Ho, Lin & Liu, 2011 (Cyclopoida: Chondracanthidae) was found on the gill filaments of the largescale tonguesole Cynoglossus arel (Bloch & Schneider) (Pleuronectiformes: Cynoglossidae). Close comparison of the specimens of B. formosana collected from off Iraq with the original description revealed some differences in elements and ornamentations on the body and appendages. Our finding of B. formosana represents not only a new record from the Indian Ocean but also from a new host.

The genus Hatschekia (Copepoda: Hatschekiidae) from pufferfishes (Tetraodontiformes: Tetraodontidae) off the Ryukyu Islands, Japan, with descriptions of four new species and a redescription of H. pholas.

Four new species of the genus Hatschekia Poche, 1902 (Copepoda: Siphonostomatoida: Hatschekiidae) are described based on female specimens collected from pufferfishes (Tetraodontiformes: Tetraodontidae) caught in coastal waters off the Ryukyu Islands, Japan: H. longiabdominalis sp. n. on Arothron hispidus (Linnaeus), H. geniculata sp. n. on A. hispidus (type host) and A. stellatus (Bloch et Schneider), H. ellipsocorpa sp. n. on A. mappa (Lesson), and H. boonah sp. n. on A. nigropunctatus (Bloch et Schneider) (type host) and A. meleagris (Schneider). Hatschekia longiabdominalis sp. n. and H. boonah sp. n. differ from all other congeners by sharing an unusual, projected abdomen and a fusiform trunk with posterior lobes; these two species are differentiated from each other by the shape of the dorsal chitinous frame on the cephalothorax. Hatschekia geniculata sp. n. can be distinguished by the combination of the following morphological characters: a rhomboidal cephalothorax with a pair of lateral conical protrusions, a cylindrical trunk with posterior lobes and a bent abdomen with a dorsal protrusion. Hatschekia ellipsocorpa sp. n. resembles H. pholas (Wilson, 1906) but can be distinguished from the latter by the possession of one distal and one inner setae on the terminal endopodal segment of legs 1 and 2. Hatschekiapholas is also redescribed based on female specimens from the tetraodontid A. stellatus. At present, 44 nominal species of the genus have been reported from Japan, including four new species described in this paper; 38 of them have been described originally from Japan.