Buizel

It has a flotation sac that is like an inflatable collar. It floats on water with its head out.

It swims by rotating its two tails like a screw. When it dives, its flotation sac collapses.

It spins its two tails like a screw to propel itself through water. The tails also slice clinging seaweed.

It inflates its flotation sac, keeping its face above water in order to watch for prey movement.

It inflates the flotation sac around its neck and pokes its head out of the water to see what is going on.

It moves freely in the water by spinning its forked tail for propulsion. The resemblance to the screw of a steamboat is coincidental.