A new species of eriopisid amphipod, Victoriopisa satsumaensis, is described from Kagoshima Prefecture, southern Japan. The new species is distinguished from its congeners by the presence of eyes, the absence of a distodorsal tuft of long setae on peduncular article 2 of antenna 1, and the shape of the palmar margin and the dactylus of gnathopod 2. The new species is most similar to V. nhatrangensis Marin and Palatov, 2022, which was recently described from Vietnam, but differs in having (1) more numerous short setae along the palmar margin of gnathopod 1, (2) 2 projections on the palmar margin of gnathopod 2, (3) a shallower median excavation on the posterior margin of gnathopod 2 dactylus, (4) several robust setae on the anterior margin of pereopods 5 and 6 carpi, and (5) more numerous distal setae on article 2 of uropod 3 outer ramus. Additionally, partial sequences of mitochondrial cytochrome c oxidase subunit I and histone H3 were determined from the type specimens of V. satsumaensis for DNA barcoding and future taxonomic studies.

Yamakado Marsh is a small, protected marsh in the mountains of northern Shiga Prefecture, with a history stretching back to the last glacial period. Although the plants, diatoms, plankton, and insects of the marsh have been studied, there are no previous reports of ostracods. For this study, nine localities in the marsh, one spring slightly above the marsh, and a pond 400 m downstream were sampled for ostracods in August 2025, yielding ten species. Two species are described as new to science, belonging to the genera Fabaeformiscandona Krstić, 1972 and Cyclocypris Brady and Norman, 1889. The new Fabaeformiscandona species, the 13th species of the genus in Shiga Prefecture, is morphologically most similar to F. okuboi Smith and Janz, 2008, a probable endemic species of Lake Biwa, located just to the south of Yamakado Marsh. The new Cyclocypris is the third species of the genus reported from Japan, with the other two known from Hokkaido, but it is most similar to the Chinese species C. pangi Yu, Ma, Wang, and Zhai, 2022.

Three new species of the genus Spectrarcturus Schultz, 1981 (Arcturidae) are described from Kumano-Basin, Japan: S. regularis sp. nov., S. bispinosus sp. nov., and S. crassibrevis sp. nov. Spectrarcturus regularis sp. nov. resembles S. murdochi (Benedict, 1898) from North Pacific and Arctic waters around Greenland, S. hystrix (Sars, 1877) from northernmost North Atlantic Ocean, and S. intermedius (Richardson, 1899) from northernmost North Pacific, in the following features: head with 2 supraocular spines; pereonites 1–3 and 5–7 each with 2 submedial spines; pleon with 6 lateral spines. However, S. regularis sp. nov. is distinguished from these three species by the following combination of characters: body covered with long spines; head with 2 supraocular spines and 2 posterior supraocular spines; pereonite 1 with 2 submedial and 4 lateral spines; pereonites 2 to 7 with 2 submedial spines. Spectrarcturus bispinosus sp. nov. is separated from its congeners by the following combination of characters: body with numerous small tubercles; pereonite 3 with 2 blunt submedial spines. Spectrarcturus crassibrevis sp. nov. differs from its congeners by the following combination of characters: pereonites 1–7 each with 2–4 short blunt submedial spines; pleotelson with 4 short blunt submedial and 2 lateral spines. This study provides the first species of the genus to be described and found in Japan, and southernmost distributional record of the genus. An amended diagnosis of the genus and key to the species are provided.

A single specimen of the rare batfish Solocisquama erythrina (Gilbert, 1905) was collected from a steep rocky seafloor off Minamidaito Island, southern Japan. The species is characterized by a bulging triangular disk and cylindrical tail, entirely covered by tubercular scales, each with a single multicuspid spine. The species had been considered as a Hawaiian endemic. However, the specimen from the Daito Islands represents the first record of S. erythrina from the northwestern Pacific region, including Japanese waters, and is further evidence of a commonality of the deep-sea fish fauna between oceanic islands in the central and western Pacific regions.

Zodariellum planum (Zhang and Zhang, 2019) (Araneae: Zodariidae), originally described from Shaanxi, central China, is newly recorded from western Honshu, Japan, on the basis of specimens collected in a vineyard. Conspecificity between males and a previously unknown female is supported by identical partial mitochondrial cytochrome c oxidase subunit I sequences. The present paper provides photographs and illustrations of both sexes, detailed description and diagnosis of the female, DNA barcode data and a distribution map. In Japan, this species is currently known only from a single vineyard population, and its occurrence there may suggest a possible introduction, although this requires further investigation.

A freshwater mussel-associated leech, Hemiclepsis kasmiana Oka, 1910, is redescribed based on newly collected specimens from Japan, including its type localities. For the first time, the redescription provides morphological information on the internal digestive and reproductive systems of Japanese populations of H. kasmiana. Molecular phylogenetic analyses based on mitochondrial cytochrome c oxidase subunit I and nuclear 18S rRNA markers also reveal that H. kasmiana is most closely related to H. khankiana Bolotov, Klass, Bespalaya, Konopleva, Kondakov, and Vikhrev, 2019, and is not recovered as a monophyletic lineage with “H. kasmiana” from Korea and the Russian Far East, highlighting the necessity of re-evaluating the taxonomic status of continental populations of this species. In addition, DNA barcoding analysis of the crop contents of the present leech specimen indicates that freshwater fishes serve as primary hosts for H. kasmiana, consistent with observations of other mussel-associated congeners.