Distribution extension of a vent scale worm Branchinotogluma bipapillata (Polychaeta, Polynoidae) in the Indian Ocean

<i>Branchinotogluma</i> Pettibone, 1985 is the most species-rich genus within the subfamily Lepidonotopodinae Pettibone, 1983, comprising 18 valid species from chemosynthesis-based ecosystems in the Pacific and Indian Oceans. Here, we report a new distributional record of <i>Branchinotoglumabipapillata</i> Zhou, Wang, Zhang & Wang, 2018, at the hydrothermal vent sites on the northern Central Indian Ridge (nCIR). This record represents the northernmost occurrence of <i>B.bipapillata</i> in the Indian Ocean. We conducted a comparative study of the nCIR population and other documented populations using distributional information, morphological traits, and genetic markers (two mitochondrial [<i>COI</i>, <i>16S</i> rRNA] and one nuclear [<i>18S</i> rRNA] genes). While most morphological characters of <i>B.bipapillata</i> were consistent with those found in the Southwest Indian Ridge (SWIR), variations were noted in the segment with the last branchiae. Molecular data revealed that all populations of <i>B.bipapillata</i> form a single clade, indicating a wide distribution from the SWIR to nCIR, covering ~4,000 km across various ridges in the Indian Ocean. This study presents extensive distribution of a vent species with well-connected populations throughout the Indian Ocean, distinguishing it from many other vent species affected by the dispersal barrier in the Indian Ocean.