Three species of monogenean, Dactylogyrus squameus Gussev, 1955, Ancyrocephalus pseudorasborae Achmerow, 1952, and Bivaginogyrus obscurus (Gussev, 1955), were collected from the gills of the cyprinid Pseudorasbora parva (Temminck and Schlegel, 1846) in Japan. Dactylogyrus squameus and A. pseudorasborae were collected in Nara, Tottori, and Ibaraki prefectures, and in Ibaraki and Okayama prefectures, respectively, and are redescribed as new country records from Japan. Bivaginogyrus obscurus has been reported from only Ibaraki and Nagano prefectures, and its discovery in Nara and Okayama prefectures as represents as new locality records. Although D. squameus and B. obscurus are known as alien parasites in Europe, all three monogeneans found in this study are considered to be native to Japan.

The taxonomy of Pleistocene and Recent microporids collected from the Pacific coast of Japan and reported previously as Micropora coriacea (Esper in Johnston, 1847), Microporina articulata (Fabricius, 1821), and Verminaria areolae Sakakura, 1935 is revised. Two new species, Micropora mawatarii and Micropora plana are described from Japanese material previously reported as M. coriacea, and Micropora rimulata Canu and Bassler, 1929 from Japan is compared with specimens from other parts of the Pacific. The differences between Microporina japonica Canu and Bassler, 1929 and M. articulata are reexamined. A new genus, Metamicropora, is erected for Verminaria areolae, which had been placed previously in Microporina.

The East Asian common octopus has long been synonymized with the Atlantic and Mediterranean species Octopus vulgaris Cuvier, 1797. However, evidence from molecular genetic studies has firmly established that the so-called cosmopolitan common octopus is in fact a group of several biogeographically distinct populations which form a complex of species with closely similar morphology. Here, a diagnosis and brief description are provided which distinguish the East Asian common octopus from O. vulgaris, and as a suitable name for it a former junior synonym of O. vulgaris is identified as a valid species: Octopus sinensis d'Orbigny, 1841. A neotype is designated. Voucher material includes specimens collected in Japan by Philipp Franz von Siebold and deposited in the National Museum of Natural History - Naturalis - in Leiden; and others that were studied by Madoka Sasaki in preparation for the detailed description of this species (as O. vulgaris) in a monograph on Japanese Cephalopoda published in 1929. At present, all species in this complex (particularly O. vulgaris and the East Asian species here identified as O. sinensis) are highly vulnerable to overfishing, so recognizing O. sinensis as a species distinct from O. vulgaris is an important step towards improving sustainable fisheries management policies for each species in this group of commercially valuable octopuses.

Kahayandrilus tundaiensis gen. et sp. nov. is described from an oxbow lake in Central Kalimantan, Indonesia. Although the taxonomic affinities are unknown, the genus differs from other genera in Tubificinae in having ovoid atria with long ejaculatory duct with uniform width, and large penes with soft and thick wall.

Three specimens of the predatory salifid leech Mimobdella japonica Blanchard, 1897 were collected from Hachijojima island, Izu Islands, Japan. This species was previously known only from Okinawajima and Amamioshima islands in the Ryukyu Islands, Japan; this is the first record of this species from the Izu Islands. A morphological description based on these specimens is presented here. In addition, we evaluated the genetic diversity of this species based on sequences of cytochrome c oxidase subunit I, tRNA^Cys, tRNA^Met, 12S rRNA, tRNA^Val, 16S rRNA, tRNA^Leu, and NADH dehydrogenase subunit 1 obtained from specimens of M. japonica collected recently from all three islands. The only difference noted among them was a unique ND1 sequence detected from two specimens collected on Okinawajima. The possibility of human-mediated introduction of M. japonica to one or more of these islands is discussed.

The taxonomic subdivision of certain Japanese freshwater amphipods into Jesogammarus jesoensis (Schellenberg, 1937), J. hokurikuensis Morino, 1985, J. fujinoi Tomikawa and Morino, 2003, and J. shonaiensis Tomikawa and Morino, 2003 was reassessed using both morphological and molecular data. Putative diagnostic morphological characters did not exhibit consistent geographic distributions, but eight geographically consistent monophyletic clades were detected based on COI and COI+12S rRNA sequence data. Uncorrected COI nucleotide divergences between the clades ranged from 7.0% to 16.4%, a level usually considered to represent inter-specific differences in crustaceans. No morphological features that differentiate the molecular clades were found. While the formal nomenclatural handling of these findings remains a problem for the future, for now we suggest the use of the term “J. jesoensis complex” to represent taxonomic entity consisting of the nominal taxa J. jesoensis, J. fujinoi, J. shonaiensis, and J. hokurikuensis, and potentially a number of hitherto cryptic taxa as well.

Ezotinorchestia gen. nov. is established to receive Orchestia solifuga Iwasa, 1939. The new genus is defined by an elongate antenna 1 (reaching the mid-point of peduncular article 5 of antenna 2), a 4-dentate lacinia of the left mandible, a mediodistally lobate article 2 and reduced article 4 of the maxillipedal palp, a deeply subchelate male gnathopod 1, the short palm of female gnathopod 1, cuspidactylate pereopods, well-developed pleopods, and the outer ramus of uropod 1 with robust setae. This genus is distinguished from Kokuborchestia Morino and Miyamoto, 2015 by the sexually dimorphic gnathopod 1 and the lack of dense, plumose setae on the pleopodal peduncles.

Twelve species of rhinoceros beetles and chafers are reported from Biak I. and Yapen I. off the northwest coast of New Guinea; three species of Neoheteronyx are described as new. Xylotrupes clinias Schaufuss, 1885 and Engertia amboinae Brenske, 1897 are reported for the Papuan region for the first time, and the range of Lepidiota reuleauxi Brenske, 1892 is extended to the Indonesian part of New Guinea. A relationship between the scarab faunas of the Schouten and Moluccan Is. is demonstrated for the first time.

The luminous deepwater cardinalfish, Epigonus macrops (Brauer, 1906), is recorded for the first time from the southeastern Atlantic (a single specimen, 121.0 mm SL) and the Timor Sea (two specimens, 128.6 and 150.8 mm SL). These specimens are described and compared with other specimens of the species from Western Australia, Indonesia, the western North Atlantic, and the Galápagos Islands. The present study reviews previous reports on the distribution of E. macrops in the world.

A rare sandperch, Parapercis fuscolineata Fourmanoir, 1985, is reported for the first time from Japan, based on a single specimen (36.8 mm SL) collected from Tosa Bay, Kochi Prefecture, Shikoku Island, at a depth of 200–203 m. This species was previously known only from the Philippines (type locality) and the tropical southwest Pacific region (Solomon Islands, Vanuatu, and New Caledonia); thus the Japanese specimen represents the northernmost record of the species. The unique coloration of P. fuscolineata, including a dark continuous stripe extending from the hind rim of the orbit to the caudal peduncle, a large black ocellus on the upper caudal-fin base, and about 12 diagonal yellowish bars on the lower half of the body, readily distinguishes this species from its congeners. The Japanese specimen is fully described, with color photographs of the fresh specimen. A new Japanese name, “Kuroobi-toragisu”, is proposed for P. fuscolineata.