Sea angels (Clione limacina) are winged molluscs that live around the world in temperate seas.  They can grow to just over three inches (8 cm) long, with blooms of them occurring near the surface in late winter.

The California berthella (Berthella californica) can grow to 2 inches (5 cm) long and looks similar to a nudibranch, but has a very thin white internal shell.