First Report of an Interstitial Semicytherura (Crustacea: Ostracoda: Cytheruridae: Cytherurinae) : a New Species from Central Japan

A new species of ostracod, Semicytherura sagittiformis sp. nov., is described from a sandy beach in Shizuoka Prefecture, central Japan. It lives in pore-waters of marine sandy sediments and is ecologically associated with other interstitial ostracods (e.g., Parapolycope and Microloxoconcha). Semicytherura sagittiformis is one of the smallest species in the genus Semicytherura, and its carapace size is comparable with those of some large interstitial ostracods. This fact suggests that a small carapace is the most important character for adaptation of ostracods to an interstitial environment.