Clione limacina lacks a shell as an adult and swims using two flapping parapodia, but its feeding apparatus is the unusual part. When it detects a Limacina sea butterfly, it everts three or more pairs of tentacle-like buccal cones from its head. Each cone bears rows of chitinous hooks that grip the prey's shell while accessory hook sacs help pull the soft body free, after which the radula scrapes out the tissue.
Field and laboratory studies dating to the 1970s describe this as an almost exclusive dietary relationship: in many populations, Limacina helicina makes up the overwhelming majority of stomach contents, and Clione appears to attack little else even when other food is offered. Individuals have also been shown to survive many months without feeding by slowing their metabolism when prey availability drops seasonally.
What is less settled is how rigid this specialism is across the species' wide Arctic-to-subarctic range; some regional studies report occasional alternative prey, and the degree of chemical versus mechanical prey recognition used to trigger the hook-cone response is still being investigated.