Marine Curios #12 - Clione limacina, or naked sea butterfly

Clione limacina, the naked sea butterfly, sounds like an angelic little creature… that eats its relatives!

The naked sea butterfly, or common clione, is a type of sea angel, a pelagic, non-shelled – or gymnosomatous – sea snail, although they are sometimes also referred to as sea slugs.

This particular species is found in the cold waters of the Arctic and North Atlantic Oceans, ranging anywhere from the surface to around 500m of depth. They are members of the order pteropoda – a name derived from the Greek ‘pteró’ for ‘wing’ and ‘pódi’, for ‘foot’ – and move by quite gracefully flapping their ‘foot’, which has evolved into a set of wings, giving the naked sea butterfly its angelic appearance.

The taxonomic classification of the species has diverged somewhat in recent years. Clione limacina has two subspecies – Clione limacina australis and Clione limacina limacina, however, three other sea angels that were previously lumped in together under the same umbrella have since been reclassified as different species – C. elegantissima, C. okhotensis, and C. antarctica, which are found in the cold waters of the North Pacific; The Sea of Okhotsk, between Japan and Siberia; and the Antarctic Ocean, respectively.

Each of the pteropods looks very similar, but the different species differ greatly in size. C. limacina can reach up to 8cm in length – making it the largest of all the known sea angels – while C. okhotensis is ten times smaller, reaching a maximum length of just 8mm.

The naked sea butterfly feeds almost exclusively on its shelled – or thecosomatous – cousins Limacina helicina and Limacina retroversa, members of the genus Limacina, which are collectively known as sea butterflies (yes, confusing!)

Its method of feeding is particularly gruesome, grabbing the shelled snails in the open water with three rings of tentacles known as buccal cones, which act the clione’s mouth. It then orientates the opening of the snail’s shell towards its cones, grabs the body with chitinous hooks everted from sacs within its mouth, and extracts the snail’s body from the shell before slurping it down whole.

Cliones are thought to live for around 2 years, and are capable of surviving for an entire year without a food source, although they halve in size during that time.

They are hermaphrodites, meaning each animal possesses both male and female reproductive organs, and they are extremely abundant, making them an important source of food for baleen whales.