Abstract
Three species of the marine mite genus Actacarus occurring on the coast of Hokkaido, northern Japan, are described. Actacarus pacificus Bartsch was found in the subtidal zone of Teuri Island ; this species is recorded from the northwestern Pacific for the first time. Actacarus illustrans Newell was taken from the intertidal zone in Oshoro Bay, the Sea of Japan. A new species, A. octosetus, is described on the basis of specimens from intertidal sandy sediment in Uchiura Bay, southern Hokkaido. The new species is easily distinguished from its congeners in having 4 pairs of perigenital setae in the female and 34-40 perigenital setae in the male. Marine suctorians are associated with A. octosetus. A key to the Actacarus species in Hokkaido is given.
