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Deep-sea cold seeps are dynamic sources of methane release and unique habitats supporting ocean biodiversity and productivity. Here, we describe newly discovered animal-bacterial symbioses fueled by methane, between two species of annelid (a serpulid Laminatubus and sabellid Bispira ) and distinct aerobic methane-oxidizing bacteria belonging to the Methylococcales, localized to the host respiratory crown. Worm tissue δ 13 C of −44 to −58‰ are consistent with methane-fueled nutrition for both species, and shipboard stable isotope labeling experiments revealed active assimilation of 13 C-labeled methane into animal biomass, which occurs via the engulfment of methanotrophic bacteria across the crown epidermal surface. These worms represent a new addition to the few animals known to intimately associate with methane-oxidizing bacteria and may further explain their enigmatic mass occurrence at 150–million year–old fossil seeps. High-resolution seafloor surveys document significant coverage by these symbioses, beyond typical obligate seep fauna. These findings uncover novel consumers of methane in the deep sea and, by expanding the known spatial extent of methane seeps, may have important implications for deep-sea conservation. 

Exploration of the deep sea off the Pacific margin of Costa Rica has resulted in the discovery of a number of new species and reports for the region. Here, we report on the occurrence of the octocoral genus Swiftia, and describe a new species collected by the Alvin submersible off the Pacific coast of Costa Rica. The new species has been observed at around 1000 m depth, growing on authigenic carbonates near methane seeps. Swiftia sahlingi sp. nov. is characterised by having bright red colonies that are with limited branching, with slightly raised polyp-mounds, thin coenenchyme mainly composed of long warty spindles, and conspicuous plates. A molecular phylogenetic analysis supports the differences between this new taxon and the closest Swiftia species. The new species represents the first record of the genus from Costa Rica and in fact for the Eastern Tropical Pacific.