Spot-Fin Porcupinefish

The spot-fin porcupinefish looks like a normal, slow-swimming reef fish until something threatens it. Then it gulps water (or air, if lifted out) and swells into a spiny ball many times its normal size, its long skin-spines standing out like a pincushion. The name comes from the fins themselves, which are dotted with dark spots. A relative of pufferfish, it carries a toxin in its skin and organs that makes it dangerous — or at least deeply unappealing — to predators that ignore the spike display.