Abstract
The phylogeography of local populations of the direct-developing estuarine polychaete Hediste atoka was examined by comparing the partial nucleotide sequences of the mitochondrial gene for cytochrome oxidase subunit I (COI) from 67 individuals collected from 27 sites that cover the majority of the distribution area of this species along the Japanese coasts, and from two sites of the Korean coasts. The phylogenetic trees drawn by four different methods (maximum likelihood, neighbor-joining, minimum evolution and maximum parsimony) showed consistently that populations of H. atoka could be divided into two parapatric forms: form A constituted all Korean and most Japanese populations except for those in southern Japan (southwestern Kyushu and the Ryukyu Islands), occupied by form B. No morphological differentiation has been detected between the two forms; the number of paragnath on the proboscis of each group was not significantly different from each other. The geographical distributions of these two forms did not overlap each other. These results suggest that cryptic speciation may occur in H. atoka.
