First record of sponge-associated deep-sea polychaete (Polynoidae: Bathymoorea) on the ultraslow-spreading Southwest Indian Ridge

We identified a rarely found deep-sea polynoid polychaete Bathymoorea, in association with a hexactinellid sponge (Dictyaulus sp.) during our marine mineral exploration expedition in the Southwest Indian Ridge (SWIR). The genus Bathymoorea appears to be restricted to the deep sea and currently includes two valid species described from the northeast Pacific region. The polychaete specimen was part of the megabenthos sample collected in a benthic sledge associated with a sponge from a water depth of 2358 m. The sponge-associated Bathymoorea is described and illustrated based on a single specimen and is the first occurrence of the genus Bathymoorea in the Southwest Indian Ocean. The morphological characteristics and phylogenetic analysis of Bathymoorea using Cytochrome C Oxidase subunit 1 (COI), 16S, and 18S gene sequences confirmed the monophyly clade for the SWIR specimen. Our finding extends the known geographical distribution of the genus Bathymoorea to the Indian Ocean. •We identified a rarely found deep-sea polynoid polychaete Bathymoorea sp., from the Southwest Indian Ridge (SWIR).•Our finding extends the known geographical distribution of the genus Bathymoorea to the Indian Ocean.•Our finding opens a new line of research on larval migration, gene flow, and evolution.