The Wavy Clio, Clio recurva (Children, 1823) is a pelagic (living in open-water) gastropod mollusk that inhabits all of the world’s oceans, at moderate depth. The adult shell measures about 20 mm (0.8 inch) and is triangular, resembling a partially flattened ice cream cone. The Wavy Clio belongs in the group of pteropod gastropods, which also includes the sea butterflies in the genus Limacina, the “canaries in the coal mine” of ocean acidification. The photo, taken by Smithsonian’s photographer K.J Osborn, shows a living Wavy Clio, with the shell covered with hydroids Pandea rubra. Hydroids are related to corals and sea anemones, and are armed with batteries of stinging cells known as cnidocytes. The cnidocytes are used by the hydroids as tools for prey capture and defensive “weapons.” In a spot-on example of mutualism, where the association of two species provides benefits for both, the Wavy Clio provides a fitting location for the hydroids to settle on, and the presence the of hydroids' cnidocytes results in protection for the mollusk.
