This paper reviews major results of taxonomical studies on Japanese species of harvestmen made by me over the past 40 years. The first attempt as a postgraduate student was to provide precise species identification of all-female populations of the curvipalpe-group of Leiobunum (Eupnoi: Sclerosomatidae) in Hokkaido. It was confirmed that they were Leiobunum manubriatum and L. globosum and they were facultative thelytokes showing typical patterns of geographic parthenogenesis. Leibunum manubriatum consisted of diploid populations with 2n=24 and tetraploid populations with 2n=ca. 48, while L. globosum was a tetraploid species with 2n=ca. 48. Population genomics analyses recently made revealed that L. globosum originated from tetraploid populations of L. manubriatum, thus L. manubriatum is paraphyletic. Most of the Japanese species of Opiliones having wide distributional ranges are polytypic and consist of many geographic races that intergrade one another by making hybrid zones where they meet. Some topics for those species revealed by cytogenetical analyses are briefly reviewed. They include chromosomal hybrid zones in several species, two cases of circular overlap in Gagrellula ferruginea, and B–chromosomes in Psathyropus tenuipes.

A checklist is compiled for 59 nominal and one unidentified species of copepods belonging to 33 genera of 12 families in two orders recorded based on the 55 original articles and monographs published from 1895 to 2020. These copepods have been found from marine mollusks including 76 species in 59 genera of 37 families in five classes in Japanese waters. A parasite-host list and a host-parasite list are also provided.

The Tokyo Imperial Household Museum bird collection held by the Yamashina Institute for Ornithology (YIO) contains many specimens originated from the United States National Museum (USNM) at the Smithsonian Institution. Although the collection includes specimens of extinct species and type specimens, the specimen information kept in the YIO is incomplete. We examined various materials such as ledgers related to the specimens from USNM to clarify the collection transfer history. Our examinations indicated that the specimens from USNM in the Tokyo Imperial Household Museum collection had been derived via three routes: USNM sent (1) 431 specimens to the present Tokyo National Museum in 1877, (2) 773 specimens to the present National Museum of Nature and Science, Tokyo (NSMT) in 1877, and (3) 117 specimens to the present NSMT in 1887. We also confirmed that almost all the specimens from USNM are remained in YIO. The present study demonstrates that ledgers and notes on specimens are useful to clarify the collection transfer history which may improve the incomplete collection data.

Two specimens (201.6–205.9 mm standard length) of Hippocampus spinosissimus Weber, 1913 (Gasterosteiformes: Syngnathidae), previously recorded from the Indo-West Pacific from India east to the Philippines, north to Taiwan, and south to northern Australia, were collected at a depth of 20 m off Tanega-shima Island, Osumi Islands, Kagoshima Prefecture, southern Japan. These specimens, described here in detail, represent the first records from Japan and the northernmost record for the species. A new standard Japanese name “Tamayori-tatsu” is proposed for the species.

A single adult specimen (348.5 mm standard length) of Lethrinus reticulatus Valenciennes, 1830 (Teleostei: Perciformes: Lethrinidae), herein described in detail, was collected from Amami-oshima island, Amami Islands, Ryukyu Islands, Japan. In Japanese waters, this species has been known only from the Okinawa and Yaeyama islands, Ryukyu Islands, and is categorized as Near Threatened by Ministry of the Environment Government of Japan. The Amami specimen represents the first record of L. reticulatus from Kagoshima Prefecture and the northernmost record for the species.

Two specimens (67.5–75.1 mm standard length; SL) of Plectranthias maekawa Wada, Senou and Motomura 2018 (Serranidae: Anthiadinae), previously recorded only the Tokara Islands, Kagoshima Prefecture, Japan, were collected from Okinawa-jima and Yonaguni-jima islands, Okinawa Prefecture, Japan. The present specimens, described herein in detail, represent the first records of the species from Okinawa Prefecture. Although the body depth (% of SL) has been regarded as one of diagnostic characters between P. maekawa and two closely-related congeners (Plectranthias helenae Randall, 1980 and Plectranthias wheeleri Randall, 1980) in the original description of P. maekawa, that of the present new specimens was overlapped with the latter two species (viz., 33.5–37.7% of SL in P. maekawa, 35.5–38.7% SL in P. helenae, and 35.6–37.9% of SL in P. wheeleri). The number of serration on the margins of subopercle and interopercle in P. wheeleri and P. maekawa has also been regarded as a diagnostic character for the two species, but additional specimens described in this study showed that the number of serration changed ontogenetically, and it overlapped in the similar-sized specimens of the two species. However, the validities of other diagnostic characters given in the original description of P. maekawa are reconfirmed in this study (viz., number of pectoral-fin rays, scales on above and below lateral line, morphometrics of body width, head length, third dorsal-fin spine length, caudal-peduncle length and depth, and both coloration of fresh and preserved conditions). In addition, three specimens of P. wheeleri (71.3–83.7 mm SL) from the Okinawa Islands, are reported here as the first records of the species from Okinawa Prefecture; it has been previously recorded from Japan (Sagami Bay, and Tokara and Amami islands), Taiwan, Indonesia, and Australasia.