The only thing better than a sea cucumber is a swimming sea cucumber (Enypniastes eximia). These echinoderms have fins where their feet should be, and they use
said fins to help them undulate and wobble across the sea bed in search
of food.
Source

The swimming sea cucumber might almost be dismissed as a balloon animal, were it not for the blood-filled viscera, that unsightly length of intestine running through it's middle.