Abstract
A new interstitial ostracod, Semicytherura uzushio sp. nov., is described from the southwest of Japan, and the details of the carapace characters of Semicytherura mukaishimensis Okubo, 1980 are redescribed. Semicytherura uzushio and S. mukaishimensis live interstitially in the intertidal and infralittoral zones, respectively. They have the smallest carapaces among the known Semicytherura species, comparable to those of other interstitial ostracods. It is thought that most of the small species belonging to this genus have an interstitial life style in marine sediments.