Abstract
A chaetiliid isopod, Symmius caudatus Richardson, 1904 is newly recorded from Korea with detailed description and illustrations. This species is characterized by the following features: head has well-defined ocular lobes anteriorly projecting; all pereonites do not have any projections dorsally; maxillule has 2 long plumose and 1 short denticulate setae on inner lobe; propodus of pereopod 1 has 11 stout circumplumose setae on ventral margin in female; and pereopod 7 is ambulatory. In this paper, we present the descriptions and illustrations of mature and juvenile males, which have not been known from previous studies, as well as those of female. We also suggested a revised diagnosis of the genus Symmius.