A New Branchipolynoe (Aphroditiformia: Polynoidae) Scale worm from Deep-Sea Hydrothermal Vents in The Onnuri Vent Field on The Northern Central Indian Ridge

Background: Deep-sea hydrothermal vents are dynamic environments with exotic faunas. In this study, we found a new species of Branchipolynoe (Aphroditiformia: Polynoidae) polynoid scale worm living in the recently discovered mussel Gigantidas vrijenhoeki in deep-sea hydrothermal vents and methane seeps at depths of 2,014 - 2,023 m. Associations between scale worms and giant mussels are common in hydrothermal ecosystems.Results: We analyzed the morphology of Branchipolynoe from the Onnuri vent field (OVF) on the northern Central Indian Ridge and sequenced the full mitochondrial genome. Based on its morphological traits and mitochondrial genes, we designated the specimens as Branchipolynoe onnuriensis n. sp., described herein. This species resembles B. longqiensis and B. tjiasmantoi, but is distinguished by its notopodial acicular lobe form and the tips of the subacicular neurochaetae. The identity of the new species was well supported by genetic distance and phylogenetic analyses of the mitochondrial c oxidase subunit I (COI) gene. Genetically, the new species is closest to the Western Pacific species B. tjiasmantoi; phylogenetic analyses support the correlation between Indian Ocean and Western Pacific hydrothermal polychaetes. This study provides a foundation for exploring the evolutionary relationship between scale worms and giant mussels.

Biological and environmental rhythms in (dark) deep-sea hydrothermal ecosystems

During 2011, two deep-sea observatories focusing on hydrothermal vent ecology were up and running in the Atlantic (Eiffel Tower, Lucky Strike vent field) and the Northeast Pacific Ocean (NEP) (Grotto, Main Endeavour Field). Both ecological modules recorded imagery and environmental variables jointly for a time span of 23 days (7–30 October 2011) and environmental variables for up to 9 months (October 2011–June 2012). Community dynamics were assessed based on imagery analysis and rhythms in temporal variation for both fauna and environment were revealed. Tidal rhythms were found to be at play in the two settings and were most visible in temperature and tubeworm appearances (at NEP). A ∼ 6 h lag in tidal rhythm occurrence was observed between Pacific and Atlantic hydrothermal vents, which corresponds to the geographical distance and time delay between the two sites.