Revisiting recent Ostracod type material from Ishizaki with insights into species distribution and taxonomic reassessment

Ishizaki's work is among the most significant taxonomic studies of recent Ostracods in Japan. However, limited access to scanning electron microscopes at that time led to several misidentifications, causing confusion in biogeographical interpretations, including the fossil record. In this study, we rephotographed Ishizaki's type specimens under an electron microscope and compared them with illustrations from papers published over the past 70 years since Ishizaki's work. This has enabled us to compile an updated synonym list and perform biogeographical assessments based on Titterton and Whatley's definitions. Of the 47 Ishizaki specimens examined, 24 species either have the oldest fossil record or are exclusively found around Japan in both fossil and modern records. Four species, originally recorded on the coast of South China, including Taiwan, are now only found around Japan: Sinoleberis tosaensis, Aurila tosaensis, Loxoconcha zamia, and Loxoconcha viva. Additionally, 15 species exhibit a wider biogeographical distribution, ranging from the South China Sea, the Indochina Peninsula, the Philippines, and Indonesia to around Japan.