A group of researchers has discovered that a tiny sea butterfly swims in a fashion similar to how an insect flies.

Not all snails are slouches--in fact, some move around underwater in a fashion similar to flying insects. 
A recent study published in the Journal of Experimental Biology notes that sea butterflies, a species of tiny molluscs, actually act a bit like fruit flies.
According to a summary of the findings, "These tiny marine molluscs gently flit around their Arctic water homes propelled by fleshy wings that protrude out of the shell opening."
This is a bit of a novel notion, as most zooplankton swim by way of paddling and dragging themselves through the water.