Samples of Middle Permian organic-rich black unconsolidated mud were collected from a fissure of black limestone in Kinshozan Mountain, Akasaka City, Gifu Prefecture, central Japan. Nine new species, one new genus and one new family are described herein: Ikeyaparchitidae Tanaka fam. nov., Gifuaparchites Tanaka and Maeda gen. nov., Aurikirkbya kinshozanensis Tanaka sp. nov., Gifuaparchites takagii Tanaka and Maeda sp. nov., Cavellina hashintotoi Tanaka and Maeda sp. nov., Bairdia nishiwakii Tanaka and Nishimura sp. nov., Bairdia akasakaensis Tanaka sp. nov., Bairdia oogakiensis Tanaka sp. nov., Bairdiacypris? hayasakai Tanaka sp. nov., Acratia? okumurai Tanaka sp. nov., and Acratia? hamadai Tanaka, Ono and Maeda sp. nov. This is the first report from Japan of a typical Panthalassa ostracod assemblage during the Middle Permian, and of which is characterized by typically endemic species.