Three new species of the eulimid gastropod genus Hemiliostraca Pilsbry, 1917, i.e., H. capreolus n. sp., H. tenuis n. sp., and H. maculata n. sp., are described and H. conspurcata (A. Adams, 1863) is redescribed based on newly obtained material from Japan. The diagnosis of the genus is also revised. Hemiliostraca capreolus n. sp. was previously misidentified as H. samoensis in museum collections and in literature. This new species was collected from Okinawa-jima Island and Amami-Oshima Island, southern Japan, and can be distinguished from H. samoensis by its distinct color patterns and markings. A recently collected specimen from an unidentified species of ophiuroid from Wakayama Prefecture, central Japan, is herein confirmed to be identifiable with H. conspurcata, which has not been recorded since its originally description from central Japan in 1863. Hemiliostraca tenuis n. sp. was collected from an unidentified species of sponge and the ophiuroid Ophiarachnella septemspinosa from Kume-jima Island, southern Japan. This new species is characterized by a slender, oval, transparent shell with indistinct brownish markings. Hemiliostraca maculata n. sp. from the Ogasawara Islands, Amami-Oshima Island, and Okinawa-jima Island, all in southern Japan, is very similar to H. conspurcata in shell appearance, but H. maculata n. sp. is distinguished from H. conspurcata by its color markings consisting of solid lines, and columella-parietal wall that forms very weak angle.

A subumbonal pit was found in the hinge of the venerid genus Ezocallista Kuroda in Kamada, 1962, for the first time. This finding supports the hypothesis that Ezocallista is more closely related to Saxidomus Conrad, 1837 than to Callista Poli, 1791. Only one Recent species, Saxidomus purpurata (Sowerby, 1852) is known from the western side of the Pacific. This species lives in temperate to cold water around Japan, Korea and in cold water in Bohai Sea in China and the Pojet, Amur and Peter the Great Bays in Russia. The oldest reliable records of this species in cool-temperate water have been recovered from the uppermost Miocene to the lowermost Pliocene Tatsunokuchi Formation in Miyagi Prefecture, northeastern Japan. That occurrence suggests that Saxidomus first adapted to a cold-water environment in its northernmost habitat during the latest Miocene to early Pliocene.

Citizen science is a powerful way to survey the distribution of alien species in a broader area and is effective in promoting public awareness. I conducted a citizen science project to survey the distribution of the alien Decollate Snail Rumina decollata in Osaka, central Honshu, Japan. This species has spread over the Prefecture in recent years. As a first step I set up ‘train station survey' in which each volunteer selects a train station in Osaka and looks for the snail on foot for 1 hour within a 1-km radius from the station. This survey revealed that the snail inhabits mainly the Senboku area (the northern part of southern Osaka). The next step aimed to investigate in greater detail the snail's distribution in the Senboku area using the following methods: 1) Grid survey: each volunteer selects a focal grid (conforming to the third-order-unit grid defined by the Statistics Bureau of Japan, ca. 1 km square) and looks for the snail within the grid for 1 hour. 2) Gathering observations from residents: fliers are handed out to municipal elementary school children and library visitors in the Senboku area, or a social networking service is used to gather snail observations from the residents. Integration of the results of these surveys revealed that the Decollate Snail occurred in fifty-one third-order-unit grids in Osaka Prefecture at the end of November 2019. Information from residents indicated that the snail had been introduced between 2000 and 2010 in Osaka and that one probable dispersal route was via gardening or agricultural materials such as soil or seedlings. The train station survey is an effective way to screen a high-density area. Observations were provided continuously for four months by residents who had found out about this project from the fliers distributed to the elementary school children. This suggests that fliers in schools may be effective in collecting observations of alien species.