Alien or native to Japan?: Whether has a planktonic copepod recently described from Shimizu Port [Japan] as a new species been introduced?

The planktonic calanoid copepod Centropages maigo Ohtsuka, Itoh and Mizushima, 2005 has been described from Shimizu Port, Middle Japan, as a new species, which was supposed to have been introduced from southeastern Asia via ballast water. Since it was first discovered from a sample collected from Japan in 1979, additional records of its occurrence all over Japan have been rapidly increasing. Whether this species is alien or native to Japan was investigated on the basis of the biology and zoogeography of other planktonic copepods. It is likely that C. maigo is widely distributed around Japan as a native species.