Order Polystilifera Brinkmann, 1917

One polystiliferan nemertean was collected at 950 m depth from non-seep seamount habitat at Cocos Canyon (SIO-BIC N263). The specimen is 65 mm long and dorso-ventrally flattened. The body is translucent and coloration is pale pinkish (Fig. 3D–E). This reptant hoplonemertean is sister to another undescribed Reptantia Brinkmann, 1917 from the Kuril Islands (500 m depth). Together with three further unidentified hadal reptant hoplonemerteans, this clade is sister to Pelagica Brinkmann, 1917 (Fig. 6). Again, we choose not to name this species as a thorough taxonomic revision of Reptantia is warranted. The histological data set is published herein: https://doi.org/10.5281/zenodo.6375286.