Inner HeartBeast question

If a Bjornaer with a Horse HeartBeast wishes to become, or at least appear to become a Hippocampus through the Mystery of the Inner Heart Beast - Chimera version, is it a snake they need to emulate, or something else? After all a Hippocampus is a sea creature.

Any fish seem better than snake IMO.

The drawings I can find all indicate a fish.
Not even an eel (tail's wrong).

I think it's supposed to be (a medieval version of) a dolphin.