Piranha is a general name used to describe a group of freshwater fish with a fearsome reputation when it comes to feeding. There are between 40 and 60 different species; none grow larger than two feet ...

Known as sand piranhas, Excirolana chiltoni are tiny crustaceans that nibble at your feet – and draw blood – if you hang out on the wet sand at the beach. They live on the Pacific coast of the U.S.