New species of capitellid polychaetes (Annelida: Sedentaria) add to the unique biodiversity of Indian Ocean hot vents

Abstract

Capitellidae constitute an important family of polychaetes valued for their usefulness as indicators of environmental health in many ecosystems, yet their diversity at mid-ocean ridges remains largely unexplored. Here, we report three species of Capitellidae across three genera from Indian Ocean ridges and formally describe two of them, including Capitella longqiensis sp. nov. from the inactive zones near the active vents of the Longqi vent field on the Southwest Indian Ridge, Notomastus sp. TVG12 from organic matter-rich sediments on the same ridge, and Decamastus branchiatus sp. nov. collected on an active vent chimney in the Edmond vent field on the Central Indian Ridge. Phylogenetic analyses support their assignment to three different genera. Within Capitella, C. longqiensis and the whale-fall species Capitella iatapiuna fell in separate subclades, indicating two independent historical colonizations of chemosynthetic ecosystems. Decamastus branchiatus is sister to an undescribed capitellid from a Red Sea vent, and Notomastus sp. TVG12 was closely related to Notomastus from Pacific nodule fields, supporting a potential biogeographical linkage between these regions. These new capitellids add to the diversity of annelids in the Indian Ocean, underlining the need for further sampling efforts to understand in full the biodiversity at these vents eyed for deep-sea mining.