It’s been a while since we last checked in with the Department of Awesome Natural Wonders. These beautiful creatures are called Sea Butterflies, which are small pelagic swimming sea snails. These particular Sea Butterflies were photographed by Russian biologist and photographer Alexander Semenov (previously featured here).
Sea Butterflies float and swim freely in the water, and are carried along with the currents. This has led to a number of adaptations in their bodies. The shell and the gill have disappeared in several families. Their foot has taken the form of two wing-like lobes, or parapodia, which propel this little animal through the sea by slow flapping movements. They are rather difficult to observe, since the shell (when present) is mostly colorless, very fragile and usually less than 1 cm in length.
[via Design Taxi]