Tokudaia
Tokudaia is a genus of murine rodent native to Japan. Known as Ryūkyū spiny rats or spinous country-rats, population groups exist on several non-contiguous islands. Despite differences in name and appearance, they are the closest living relatives of the Eurasian field mouse ("Apodemus"). Of the three species, both "T. osimensis" and "T. tokunoshimensis" have lost their Y chromosome and "SRY" gene; the sex chromosomes of "T. muenninki", on the other hand, are abnormally large. Named species are: At least "Tokudaia osimensis" may be a cryptic species complex.