A single large specimen (MUFS 18880, 739 mm in standard length) of polynemid fish, Eleutheronema tetradactylum (Shaw, 1804), collected by a large set net off the mouth of Azuma River, Fukaura, Aomori, northern Japan, represents the first reliable record from Japan and northernmost record of the species. Furthermore, a lateral line squamation character on the caudal fin membrane is herein described as newly-recognized diagnostic character for the species. Eleutheronema tetradactylum is characterized as follows: four pectoral filaments; lower jaw lips restricted to posterior one-third of lower jaw, vomer with tooth plates on either side; lateral line on caudal fin membrane divided into three lines.
