[1] Sea butterflies (thecosomata) are pelagic marine gastropods, so called because they swim by flapping their wing-like parapodia.

Towards the anterior end of the animal, two parapodia (winglike flat lobules) protrude between each half of the shell.

The parapodia enable these sea butterflies to float along in the water currents, using slow flapping movements.

The parapodia are also covered with cilia, which produce a minute water current that pushes the planktonic food to the mouth of the animal.

At the same time, the subfamilies were given the new status of families: Cavoliniidae, Cliidae, Creseidae and Cuvierinidae (Cainozoic Research, 2(1-2): 163-170, 2003).