Distribution of four Hediste species (Polychaeta: Nereididae) in estuaries in Korea and Japan, with special reference to an undescribed species newly found from Han River Estuary

초록

Hediste species (Nereididae) often dominate in estuarine macrobenthic fauna in the North Temperate Zone; three species are currently known in eastern Asia. They are morphologically similar, but distinguishable by reproductive and developmental characteristics and mitochondrial 16S rRNA genes. In the present study, we examined Hediste specimens collected from many locations in Japan and Korea to clarify the geographical distribution of each species. During this survey, an undescribed species, which has unique characteristics of the epitokous metamorphosis, was found from Han River Estuary in Korea. Our results show that four Hediste species with markedly different reproductive characteristics are distributed in eastern Asia as follows: (1) H. atoka Sato and Nakashima, 2003: benthic reproduction without epitokous metamorphosis, direct development with 200–250 µm in egg diameter, widely distributed throughout Japan (from Hokkaido to Ishigaki-jima Island) and Korea (both the east and west coasts; (2) H. diadroma Sato and Nakashima, 2003: swarming with marked epitokous metamorphosis (addition of epitoke-specific sesquigomph spinigers in middle parapodia), 1-month planktonic development with 130−170 µm in egg diameter, distributed in Japan (from Hokkaido to Kagoshima) and Korea (southeast coast); (3) H. japonica (Izuka, 1908): swarming with slight epitokous metamorphosis (increase in number of homogomph spinigers), 10-day planktonic development with 180–210 µm in egg diameter, distributed in Japan (Ariake Sea) and Korea (throughout west coast); (4) H. sp. (undescribed species): swarming with marked epitokous metamorphosis (addition of many homogomph spinigers and enlargement of notopodial dorsal ligule in middle and posterior parapodia), developmental mode unknown with around 200 µm in egg diameter, endemic to Han River Estuary in Korea.