Polychaetes distributed across oceans—examples of widely recorded species from abyssal depths of the Atlantic and Pacific Oceans.

This article investigates the distributional ranges of selected deep-sea annelid species using an integrative approach combining mitochondrial COI genetic markers, 18S rRNA sequences, and detailed morphological analyses. Specimens collected from multiple deep-sea expeditions across the Pacific and Atlantic Oceans between 1998 and 2015 were studied, focusing on species with documented widespread deep-sea distributions and sufficient sample sizes. The study confirms pan-oceanic distributions for three species—*Sigambra magnuncus* (Pilargidae), *Progoniada regularis*, and *Bathyglycinde profunda* (both Goniadidae)—and identifies several new species, including *Octomagelona borowskii* (Magelonidae) and two *Spiophanes* species (Spionidae). Genetic data reveal high haplotype diversity and suggest ongoing dispersal and gene flow between oceans, likely facilitated by larval transport and sediment-mediated dispersal via abyssal storms and near-bottom currents. The findings highlight the complexity of deep-sea species connectivity and emphasize the need for further sampling and integrative studies to better understand deep-sea biodiversity and biogeography.