The feeding habits of the rhizostome Netrostoma setouchianum (Kishinouye, 1902) collected from the central part of the Seto Inland Sea, Japan was examined based on observations of the structure of secondary mouths and contents in the canals and stomach. The mouths were oval, approximately 365 μm along the major axis and 130 μm along the minor axis. Small-sized planktonic copepods such as Paracalanus parvus s.l. and Oithona sp. were found in the canals and had body widths that fell well within the size of the mouths.