ABSTRACT
The hyporheic water mite Yachatsia elliptica is newly recorded from southern Japan. This species was originally described as Ussuriaxona elliptica from the Far East. And Ussuriaxona is proven to be synonymous with Yachatsia. The species is distinguished from the North American species Y. mideopsoides in having a horn-like ventral projection on palpal femur and rounder idiosoma. Taking the whole distributional record into consideration, Yachatsia is revealed to show trans-Pacific disjunct distributions between northeastern Asia and western North America. A plausible scenario for the formation of the current distribution of Yachatsia is suggested.
Acknowledgments
I am grateful to Dr. Aki Tanaka (Kumamoto Univ.) and Mr. Gyo Yoshinari (IDEA Consultants, Inc.) for giving me an opportunity to examine the Yachatsia specimen collected in Japan. I am especially indebted to Dr. Nobuo Tsurusaki (Tottori Univ.) for his invaluable comments on the historical biogeography of arachnids. I also thank Dr. Reinhard Gerecke (Tübingen) and anonymous reviewers for their constructive comments on a previous version of manuscript.
Disclosure statement
No potential conflict of interest was reported by the author.