Taxonomy and ecological insights into Melinnopsis shinkaiae sp. nov., a polychaete with a vertical tube from the Daiichi-Kashima seamount (Northwest Pacific)

Abstract

Melinnopsis shinkaiae sp. nov. represents the fifth species of the genus Melinnopsis to be discovered in Japan. The new species was collected using the submersible Shinkai 6500 at 3623 m depth of Daiichi-Kashima Seamount, a locality with relatively unexplored biodiversity. Our in-situ observation revealed that the species inhabits the upper end of a vertical tube built on the seafloor. The species is differentiated from its congeners by combination of the following morphological characteristics: i) the presence of 12 thoracic uncinigers; ii) the absence of a postbranchial dorsal membrane; iii) the arrangement and shape of four pairs of branchiae; iv) thoracic uncini with a small basal tooth on each three teeth above the rostral tooth; v) absence of longitudinal groove in the large buccal tentacle.