Sea anemones are diverse and ecologically successful members of Anthozoa. They are often found in intertidal and shallow waters, although a few of them inhabit harsher living conditions, such as deep-sea
hydrothermal vents. Here, we sequenced the transcriptome of the vent sea anemone Alvinactis sp., which was collected from Edmond vent along the central Indian Ocean ridge at a depth of 3275 m, to explore the
molecular mechanisms related to adaptation to vents. Compared with another deep-sea anemone (Paraphelliactis xishaensis) and five shallow water sea anemones, a total of 117 positively selected genes and 46 significantly expanded gene families were found in Alvinactis sp. specifically that may be related to its vent-specific aspect of
adaptation. In addition, 127 positively selected genes and 23 significantly expanded gene families that were found in both Alvinactis sp. and P. xishaensis. Among these, vent-specific adaptations of Alvinactis sp. may involve genetic alterations in peroxisome,ubiquitin-mediated
protein degradation, oxidative phosphorylation, and endocytosis,
and its deep-sea adaptation may involve changes in genetic information processing. Differentially expressed genes between Alvinactis sp. and the deep-sea anemone P. xishaensis were enriched in a variety of pathways related to adaptation, such as energy metabolism, genetic information processing, endocytosis, and peroxisomes. Overall, we provided the first transcriptome of sea anemones that inhabit vents, which enriches our knowledge of deep-sea hydrothermal vent adaptation and thediversity of sea anemones.