A new species of the genus Travisia Johnson, 1840, the single genus of the family Travisiidae, is described. Specimens of Travisia sanrikuensis sp. nov. were collected in the Sanriku region, Japan, from the lower bathyal zone (871–1684 m depth) of the northwestern Pacific. Molecular phylogenetic analysis based on partial 16S rRNA gene sequences revealed that the new species is phylogenetically close to Travisia brevis Moore, 1923, but differs from all congeneric species by the following morphological characters: 25 segments, 20 chaetigers, and 19–20 pairs of cirriform branchiae starting from chaetiger 2.

Specimens of two species of lernaeopodid copepods, Salmincola edwardsii (Olsson, 1869) and Salmincola markewitschi Shedko and Shedko, 2002, were collected from chars (Salvelinus spp.) reared in exhibition tanks of the Sapporo Salmon Museum, Hokkaido, Japan. Descriptions of these copepods are provided using the specimens. In 1988, adult females of S. edwardsii were found on the gills of southern Asian Dolly Varden, Salvelinus malma krascheninnikova Taranetz, 1933, and those of S. markewitschi in the buccal cavity of whitespotted char, Salvelinus leucomaenis (Pallas, 1814), Nikko char, Salvelinus leucomaenis pluvius (Hilgendorf, 1876), and brook trout, Salvelinus fontinalis (Mitchill, 1814). These copepods are considered to have been introduced to the museum in the late 1980s along with wild chars transported live from natural waters of Hokkaido. Adult copepods have been manually removed using forceps once or twice a year from reared chars, but such infrequent practices have not been effective to eliminate S. markewitschi, which was thus collected again in 2020. In contrast, S. edwardsii was completely eliminated by stopping rearing an infected population of southern Asian Dolly Varden, to which this parasite is host-specific.

A new species from the cockroach genus Eucorydia Hebard, 1929 from Miyako-jima Island of the Nansei Islands in Southwest Japan was compared to six closely related congeners; E. yasumatsui Asahina, 1971; E. donanensis Yanagisawa, Sakamaki, and Shimano, 2020; E. tokaraensis Yanagisawa, Sakamaki, and Shimano, 2020; E. dasytoides (Walker, 1868); E. guilinensis Qiu, Che, and Wang, 2017; and E. pilosa Qiu, Che, and Wang, 2017. The new species Eucorydia miyakoensis Yanagisawa, Sakamaki, and Shimano, sp. nov. from Miyako-jima Island was characterized by a small overall male body length of 12.5–13.0 mm and tegmina with an uninterrupted orange transversal band in the middle, and a pair of orange pubescent patches at the base. Eucorydia yasumatsui, E. donanensis, E. tokaraensis, the zonata population of E. dasytoides, and E. miyakoensis were divided into five lineages in a maximum likelihood tree generated from a dataset concatenated from five molecular markers (two nuclear: 28SrRNA and histone H3, and three mitochondrial: COII, 12SrRNA, and 16SrRNA). We recognized E. miyakoensis as a distinct species, which was also supported by the pairwise genetic distances (3.4%–6.7%, K2P) of the COI sequences to the other Japanese Eucorydia species.

The sea anemone Capnea japonica (Carlgren, 1940) was described based on two specimens collected in 1914 off the coast of Misaki, Sagami Bay, Japan. Besides the two syntypes, no further specimens are known to have been collected. The original description of C. japonica is brief, and, therefore it is difficult to identify the species based on the available information. In 2014, we collected a single specimen of Capnea Gosse, 1860 from around the type locality of C. japonica and examined its morphological characters, such as the external features, cnidome, and musculature, and then compared it with the syntypes of C. japonica. The characteristic form of tentacles, size and distribution of cnidae, and very strong sphincter muscle in our specimen were a good match to the original description and to the results of examining the syntypes. Based on the topotype and syntypes, we redescribe C. japonica and show its phylogenetic position with newly obtained DNA sequencing data.

Yunohamella varietas sp. n., from Ulsan Metropolitan City, Korea is newly described based on the male. The new species is closely related to Yunohamella lyrica (Walckenaer, 1841) and Yunohamella serpatusa (Guan and Zhu in Zhu et al., 1993), but can be distinguished from Y. lyrica and Y. serpatusa by the dorsal pattern of the abdomen, shape of embolus, conductor and median apophysis. The new species was collected with a sweep net in rice fields.

Difflugia biwae Kawamura, 1918 has been redescribed. Here, the neotype of D. biwae, which was newly collected from its type locality, Lake Biwa, is designated to the species to clarify its taxonomic status. Morphometric characterization of D. biwae was performed. A statistically significant correlation between body length and shell collar diameter was identified in the population of the Lake Biwa, but this correlation was not significant in the population from the Mulan Lake. The PCA scatterplot indicates that the Mulan Lake population could be a separate taxon identified by shorter protuberance length and body length.

A single specimen of Bassozetus mozambiquensis Tomiyama, Takami, and Fukui, 2016, collected off southern Brazil in the western South Atlantic and held in the University of Hamburg ichthyological collection, was re-examined. Because the species was previously known only from the western Indian Ocean, solely on the basis of the holotype, the present specimen represents not only the first Atlantic record of the species, but also a ca. 8300 km westward extension of the distributional range. A detailed description of the Atlantic specimen and an updated diagnosis of the species are provided.

Specimens of the genus Eucorydia Hebard, 1929 from Chiang Mai, northern Thailand, were compared with eight closely similar congeners: E. aenea (Brunner von Wattenwyl, 1865), E. dasytoides (Walker, 1868), E. yunnanensis Woo, Guo, and Feng, 1986, E. pilosa Qiu, Che, and Wang, 2017, E. guilinensis Qiu, Che, and Wang, 2017, E. tangi Qiu, Che, and Wang, 2017, E. linglong Qiu, Che, and Wang, 2017, and E. tokaraensis Yanagisawa, Sakamaki, and Shimano, 2020, and turned out to be a different species from eight congeners. This species from Thailand is characterized by the specific male genitalia shape: right phallomere 2 (R2) slightly elongated, the basal left area of R2 forming a triangular protrusion, and the basal half of left phallomere 7 (L7) protruded to the left with long spatulate distal half and with a beak-like apex. This species is also characterized by the tegmina containing three orange markings in the middle, and with a pair of orange markings at its base. Based on the above, this species is described as a new species, Eucorydia asahinai sp. nov.

Eighteen specimens of Sardinella gibbosa (Bleeker, 1849) collected from Okinawa Island, Ryukyu Islands, Japan represent the first Japanese specimen-based records of the species. All specimens conformed closely to the diagnosis of S. gibbosa, having the caudal fin uniformly pale, a black spot on the dorsal-fin origin, body scales with centrally discontinuous striae, 26−31+50–57=77–88 gill rakers on the first gill arch, and 18 or 19+14 or 15=32–34 keeled scutes along the body ventral surface. In addition, some previous Japanese records of unidentified clupeoid fishes are reviewed.

The spelling of the specific name monticolus in the scientific name of a spider, Cybaeus monticolus Kobayashi, 2006, does not violate any relevant provisions of the International Code of Zoological Nomenclature. This spelling is, therefore, the “correct original spelling” of the specific name under Article 32.2 of the Code. Regardless of whether this name is deemed an adjective or a noun in apposition, it should be maintained unaltered when it is combined with the generic name Cybaeus L. Koch, 1868, the gender of which is masculine. The later spelling monticola, as presented in the combination Cybaeus monticola in a recent arachnological treatise and then in an important online taxonomic resource from which its use appears to be spreading, is an “incorrect subsequent spelling” under Article 33.3 of the Code.

Adult male and larva of Gnathia capitellum sp. nov. (Crustacea: Isopoda: Gnathiidae) are described. The specimens were laboratory-reared larvae that infested host fishes collected by longline fishing in a coastal bay of Izu Peninsula and adult males found in dredge samples from shallow water (depth: 11–12 m) of Miura Peninsula, central Japan. Adult males of G. capitellum sp. nov. were easily distinguished from the other species of Gnathia Leach, 1814 from around the world by the small oval head and the inner margin of pylopod without plumose setae. Most other Gnathia species have a large rectangular head and plumose setae present on the article 1 of pylopod. Appearance of the adult male resembles the genus Afrignathia Hadfield and Smit, 2008 rather than Gnathia but Afrignathia has maxilla 1 which is absent in all known male gnathiids in the world including G. capitellum sp. nov. Fish parasitic larva of G. capitellum sp. nov. is also described herein. This larva closely resembles larvae of the genus Gnathia, but can be distinguished from the other Gnathia species by the remarkably oval-shaped basis in pereopods 2–4.

Sodium hypochlorite has been used for cleaning specimens of freshwater and brackish water snails that are covered with deposits. Our experiments using specimens of two freshwater snail species, Semisulcospira niponica (Smith, 1876) and S. reticulata Kajiyama and Habe, 1961, showed that this traditional method could remove thin deposit layers, including algae, but was not useful for obstinate deposits. We found that a new method using ammonium thioglycolate could be applied to remove obstinate iron-rich deposits. Though ammonium thioglycolate treatment caused loss of gloss inside the aperture, this loss could be prevented by plugging a kneaded eraser into an aperture. Moreover, the new method could clean specimens with little damage of the periostracum. So as to remove deposits with the least damage to shells, 3% w/v sodium hypochlorite was useful for deposits including algae, and 20% w/v ammonium thioglycolate was suitable for cleaning specimens with iron-rich deposits. Degeneration of the microstructure of inner whorls can be avoided by plugged shell apertures with a kneaded eraser in both methods. Shell deposits that are composed of both algae and iron should be treated first with 20% w/v ammonium thioglycolate, and then with 3% w/v sodium hypochlorite to remove the deposits. Appropriate cleaning methods enable accurate examination and long-term preservation of shell specimens.

Caprella nojimaensis sp. nov. (Crustacea: Amphipoda: Caprellidae), inhabiting the gorgonian Calcigorgia gracilis Matsumoto, van Ofwegen, and Bayer, 2019, is described based on a specimen from 1497 m depth in the Nojima Submarine Canyon, off Boso Peninsula, central Japan. The species is closely related to C. gracillima Mayer, 1890, but differs from the latter in gnathopod 2 being positioned near the anterior margin of pereonite 2 and in the presence of paired small mid-dorsal projections on pereonites 2 and 5. The body colour of live material is pale pink, with mouth parts and gnathopod 2 fringed with darker pink, revealing protective colouration that matches that of the host gorgonian. The clinging behaviour in situ is “upright” as recorded by the remotely operated vehicle Hyper-Dolphin, and the presence of dense swimming setae on antenna 2 suggests that the caprellid feeds by filtering material suspended in the bathyal zone.

This study describes a new species of the subfamily Coelotinae (Agelenidae) from Kinki district, central Japan, under the name of Coelotes nojimai sp. nov. It resembles C. yodoensis Nishikawa, 1977 and C. nagaraensis Nishikawa, 2009 but is characterized by a male palp with a large and greatly curved conductor and slender spermathecae in the internal genitalia of female specimens. The morphological differences and distribution ranges of these three species have been discussed in detail. In addition, the mitochondrial cytochrome c oxidase subunit I (mt-COI) partial sequences of the new species have been analyzed and documented for future use.

Members of the family Haloclavidae, belonging to the order Actiniaria, are characterized by the presence of a large siphonoglyph next to their actinopharynx and an aboral end without a basal disc. Members of the genus Haloclava Verrill, 1899 have been reported primarily from Europe and America, and have not yet been described from Japanese waters based on the collected specimen. In this study, I describe a new species, Haloclava hercules sp. nov., from the Pacific coast of Japan. This new species is chiefly characterized by cudgel-like blunt massive tentacles with knob-like acrospheres in the outer tentacular cycle and gigantic basitrichs over 250 µm in length, which are the largest known from sea anemones.

A copepod, Pseudanthessius chuukensis Uyeno, n. sp. (Cyclopoida: Pseudanthessiidae), is described based on the type specimen obtained from the grouper Epinephelus sp. (Actinopterygii: Perciformes: Serranidae) caught in Chuuk Lagoon (North Pacific Ocean), Federated States of Micronesia, North Pacific Ocean. The copepod differs from its congeners in the following female characters: the urosome is 5-segmented; caudal rami are five to six times longer than wide; the distal endopodal segment of leg 1 carries three spines and three setae; leg 4 endopod has two setae, without proximal swellings, and as long as about two-third of that of the exopod. This finding of the copepod is the first record of the family Pseudanthessiidae from the actinopterygian fish.

The cestode fauna of murid and cricetid rodents in Hokkaido, the northernmost island of Japan, was evaluated based on our parasite collection and a review of the literature. Adult and larval cestodes collected from Apodemus speciosus (Temminck, 1844), Myodes rufocanus (Sundevall, 1846), and Rattus norvegicus (Berkenhout, 1769) in Hokkaido were identified by both morphological and molecular diagnoses. A total of 10 species from 5 families were confirmed in our collection. Arostrilepis tenuicirrosa Makarikov, Gulyaev, and Kontrimavichus, 2011, Paranoplocephala kalelai (Tenora, Haukisalmi, and Henttonen, 1985), and Taenia crassiceps (Zeder, 1800) were recorded for the first time from Hokkaido. A comprehensive look at both the present and previous studies revealed that the cestode fauna of rodents in Japan consists of at least 30 species from 6 families. Among them, 23 species occur in Hokkaido. The species composition is strongly affected by the nearby Eurasian continent, suggesting parasite migrations with rodent hosts over land bridges between Hokkaido and Sakhalin and between Hokkaido and Honshu, the main island of Japan. A DNA barcoding system using sequences of nuclear 28S rDNA and mitochondrial cox1 allowed us to identify cestodes at species and genus levels, even in different developmental stages. The integration of morphological and molecular diagnoses is essential in cestode taxonomy to establish a common ground for biogeographical studies worldwide. The standardization of DNA barcoding is particularly of critical importance.

The feather mite Pseudalloptinus milvulinus (Trouessart, 1884) was collected from feathers of the Black Kite Milvus migrans (Boddaert, 1783) in Ishikawa Prefecture, Japan, in 2019. The identification of this mite was based on the form and arrangement of setae on the idiosoma and aggenital region. This study is the first report of this mite species and the genus Pseudalloptinus Dubinin, 1956 in Japan.

Ocosia spinosa Chen, 1981 (Tetrarogidae) is newly recorded from the Pacific coast of Japan, on the basis of 10 specimens (31.3–78.1 mm standard length), having been previously reported only from Taiwan. A revised diagnosis for the species, based on the Japanese specimens plus a single specimen from Taiwan, is given as follows: XV–XVIII, 7 or 8 dorsal-fin rays; III, 4–6 anal-fin rays; usually 13 (rarely 12) pectoral-fin rays; 12–18 lateral-line pores on body; 6–15 gill rakers; usually 28 (rarely 27) vertebrae; 2nd dorsal-fin spine longest, slightly longer than 3rd spine; interspinous dorsal-fin membranes of middle portion of dorsal fin incised for one-fourth to one-third of each spine length; dorsal profile of snout concave; posterior lacrimal spine directed backward, its length about 2–3 times greater than that of anterior lacrimal spine; small lateral lacrimal spine usually present (absent in larger specimens); small spine usually present at anterior end of suborbital ridge in smaller specimens (absent in larger specimens); weak stubby papillae covering upper lip and anterior half to one-third of lower lip; trunk uniformly brownish-red when fresh, without distinct markings (but with faint brownish small blotch near base of middle portion of dorsal fin in some individuals). Although the presence or absence of small spines on the lateral surface of the lacrimal and anterior end of the suborbital ridge has previously been regarded as an important diagnostic character of O. spinosa, examination of the present specimens showed that the character changes with growth. The present specimens represent the first Japanese records, as well as the northernmost and easternmost records for the species. The new English and Japanese standard names “Red Waspfish” and “Aka-hachiokoze”, respectively, are proposed for O. spinosa.

An ovigerous female of a fish ectoparasite Argulus caecus C. B. Wilson, 1922 was collected from a squid, probably Todarodes pacificus (Steenstrup, 1880), from a fixed net installed in Otsuchi Bay, an inlet of the northwestern Pacific Ocean, Iwate Prefecture, northen Japan. Since the original description of A. caecus was insufficient, this paper reports on the morphology of the species based on a detailed examination of the female. In particular, the first and second antennae, the first and second maxillae, and four pairs of legs, whose features were poorly known, are reported in detail. The specimen of A. caecus is inferred to have detached itself and moved from a fish host, perhaps a coastal puffer, to the squid while these two animals were trapped in the net or when they were removed from the net. Following Argulus scutiformis Thiele, 1900, A. caecus is the second species of Argulus found from northern Japan located in the northern temperate or subarctic region, and its occurrence in this region is likely to be affected by the Tsushima Warm Current and its branch, the Tsugaru Warm Current, both of which flow off the coast of the region.

Investigations were carried out on 22 deep-water octocoral specimens in the family Coralliidae sampled from the Emperor Seamounts during 2009 to 2012. The specimens were collected from 350–1100 m deep, mostly from the southernmost region of the Emperor Seamounts. Colonies were identified by visual and microscopic observation of standard morphological characters (colony size, diameters of colony base and branches, diameter and height of autozooid mound, thickness of coenenchyme and sclerite sizes, etc.) along with supporting information from molecular DNA analysis. Half of the 22 specimens were identified as Pleurocorallium cf. pusillum (Kishinouye, 1903), suggesting that the species called “Mid” that was once harvested dominantly in this area was this species. The remaining 11 specimens were identified as genus Hemicorallium Gray, 1867. These were identified as belonging to the following species: one previously described species [H. laauense (Bayer, 1956)], three similar species [H. cf. abyssale (Bayer, 1956), H. cf. regale (Bayer, 1956), H. cf. sulcatum (Kishinouye, 1903)] and three new species (H. kaiyo sp. nov., H. muzikae sp. nov. and H. tokiyasui sp. nov.).

A single specimen of Muraenichthys gymnopterus (Bleeker, 1853) was collected from a sandy intertidal flat having rocks and dead corals in the estuarine area of Nagura Amparu, Ishigaki-jima Island, southern Japan, in October 2020. This specimen collection constitutes the first record of M. gymnopterus from Japanese waters. In this study, the diagnostic characters between M. gymnopterus and M. hattae Jordan and Snyder, 1901 are provided, based on our morphological observations of 37 specimens, including Okinawan specimen, and previous studies, as follows: head length [M. gymnopterus 11.8–15.0% of total length (TL) vs. M. hattae 9.4–11.0%], trunk length (24–25.4% of TL vs. 28–31%), the horizontal distance from the dorsal-fin origin to a vertical line through the anus 73–87% of head length vs. 13–49%), the number of vertebrae (total 129–130 vs. 148–155; predorsal 30 vs. 47–53; preanal 41–44 vs. 51–55), the number of the lateral-line pores before the anus (43–45 vs. 51–55). Additionally, the body depth at the gill opening in TL and the trunk length in TL can also be used to distinguish between these two species (2.8–3.7% of TL vs. 1.4–3.0%). Although M. gymnopterus has previously been reported from tropical to temperate regions, we suspect that the records from temperate regions are based on misidentification of M. hattae.