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 o
(Wikipedia)