First record of the rare spoon worm <i>Ikedosoma elegans</i> (Annelida: Echiura: Thalassematidae) from Shikoku Island, Japan

Abstract

Ikedosoma elegans (Ikeda, 1904) (Annelida: Echiura: Thalassematidae) is a rare, large deep-burrowing spoon worm that has been observed only in Japan. This species was first described based on the specimens collected from Misaki, Sagami Bay (Kanagawa Prefecture), eastern Japan, in 1902. Since the first description, this species has not been collected until the recent studies, which reported that I. elegans was collected from Hamana Lake (Shizuoka Prefecture), Boso Peninsula (Chiba Prefecture), and probably Amakusa, Ariake Sea (Kumamoto Prefecture). Furthermore, the specimen collected from Takasu, Seto Inland Sea (Okayama Prefecture) in 1975 was identified to be I. elegans. In this study, we present a new locality of this species in Japan. We collected a large individual of I. elegans with a probably commensal scale worm (Polynoidae: Polynoinae) by using a yabby pump in a mud flat in the Doki River Estuary, which is facing the Seto Inland Sea, in Marugame (Kagawa Prefecture), northern Shikoku Island. To the best of our knowledge, the present study is the first record of I. elegans from Shikoku Island and the second record from the Seto Inland Sea, following a 42-year-old record from Takasu, Okayama.