A review of Asian Hediste species complex (Nereididae, Polychaeta) with descriptions of two new species and a redescription of Hediste japonica (Izuka, 1908) [Review]

摘要

Three Asian species of the genus Hediste (Nereididae, Polychaeta, Annelida), including two new species, are reviewed. Hediste japonica (Izuka, 1908) was redescribed based on recently discovered type material and on additional specimens newly collected from the Ariake Sea in Japan and the west coast of Korea. Two new species, H. diadroma and H. atoka, were described based on specimens collected from Japan. These three species are morphologically similar, but distinguishable by some differences in parapodial and chaetal morphology, at least at the sexually mature stage. The presence of homogomph falcigers and the absence of heterogomph spinigers are unique characteristics of H. japonica among this genus. Inconspicuous epitokous metamorphosis occurred as a slight enlargement of the eyes and parapodial ligules in mature adults of H. diadroma sp. nov. and H. japonica in combination with their reproductive swarming and pelagic larval development. The epitoke-specific sesquigomph spinigers were added in mature adults of H. diadroma sp. nov., while the number of ordinary homogomph spinigers increased in some adults of H. japonica. Epitokous metamorphosis in the Hediste species was compared with that in other nereidid genera. No epitokous metamorphosis was observed in H. atoka sp. nov., corresponding to its reproduction without swarming and to its development without a planktonic larval stage. Significant differences in paragnath numbers in the maxillary ring of the proboscis were found among the three species, suggesting different feeding habits. In Japan, the present distribution of H. japonica is restricted to muddy tidal flats in the inner part of the Ariake Sea, probably due to recent human impact, while the other two species are widespread.