At first glance, the animal kingdom has no shortage of tails. From crocodiles to platypuses, squirrels to pigs and fish to boa constrictors, the shapes, sizes and textures are diverse. But whether flat, flexible, paddle-like, scaly, bare, mighty, curly or fluffy, all tails have one thing in common: they are roughly circular in cross-section. Of all the tails in all the world, there’s just one that differs. And it belongs to the seahorse.