Rolling in the deep: peculiar rolling behaviour observed in deep-sea anemones

Abstract

Deep-sea anemones (Cnidaria: Anthozoa) are regarded as sessile organisms, living in fine sediments, attached to hard substrates, or living as epibionts on other organisms. Motility in Actiniaria is not well documented and is often overlooked, typically limited to anecdotes, personal observations or time-lapse recordings. Known motility is usually limited to slow gliding that is only observable over long periods of time. However, some species have adapted the ability to swim for predator evasion, modifying their shape to move around with the currents. In this study we report in situ observations of rolling sea anemones from the submersible Bakunawa at 6014 m in the Nova Canton Trough (West Pacific Ocean). These new observations highlight a new method of locomotion in actiniarians where they appear to use their tentacles to grip the substrate to aid their rotation; this enables them to slowly move across the seafloor on their side, 90° to their conventional sessile upright position. When approached by the submersible, the sea anemone ceased its rolling locomotion, suggesting a mechanoreception related response.