Solvin Zankl / Sea butterfly (Cavolinia uncinata) deep sea species from Atlantic Ocean off Cape Verde. Captive.

Juergen Freund / Sea butterfly, also known as Thecosomata or flapping snail, Lizard Island, Queensland, Australia, April 2008

Juergen Freund / Sea butterfly, also known as Thecosomata or flapping snail, Lizard Island, Queensland, Australia, April 2008

David Shale / Sea butterfly mollusc {Clio sp} Atlantic ocean. Deepsea species

Tony Wu / Sea butterfly (Cavolinia uncinata),small pelagic mollusc, using nets of mucus to capture food. East China Sea, Kagoshima Prefecture, Japan.

Tony Wu / Sea butterfly (Cavolinia uncinata), small pelagic mollusc using nets of mucus to capture food. East China Sea, Kagoshima Prefecture, Japan.

Frederique Olivier / Sea butterflies / Pelagic swimming sea snails (Thecosomata) drifting with the current, Bellot Strait, Nunavut, Canada.

Solvin Zankl / Close up of Sea butterfly (Diacria trispinosa) translucent body, deep sea species from Atlantic Ocean off Cape Verde. Captive.

Solvin Zankl / Portrait of Sea butterfly (Diacria trispinosa) deep sea species from Atlantic Ocean off Cape Verde. Captive.

Solvin Zankl / Portrait of Sea butterfly / Thecosomata (Cuvierina spoeli) from Atlantic Ocean off Cape Verde. Controlled conditions.

Solvin Zankl / Portrait of planktonic Sea butterfly (Clio pyramidata) or Thecosomata Atlantic Ocean, close to Cape Verde.

Magnus Lundgren / Shelled pteropod (Diacria major) swimming with the tentacles out. Balayan Bay, off Anilao, Batangas, Philippines, Pacific Ocean