A new species of the genus Arhynchite (Annelida, Echiura) from sandy flats of Japan, previously referred to as Thalassema owstoni Ikeda, 1904.

A new echiuran, Arhynchite hayaoi sp. n., is described from newly collected specimens from sandy flats of the Seto Inland Sea, Japan, together with many museum specimens, including those once identified as Thalassema owstoni Ikeda, 1904 or Arhynchite arhynchite (Ikeda, 1924). The new species is clearly distinguishable from its congeners by the smooth margin of gonostomal lips and lack of rectal caecum. Brief references are also made to the morphological distinction between the new species and Thalassema owstoni, originally described from the deep bottom on the Japanese Pacific coast.