In the years and centuries after the fall of civilization, the scattered remnants of mankind lack the sophistication that they once had, and so the names they give to creatures lack the taxonomical grace of those which their ancestors use.
This is not to say that they are stupid, though; no creature which was could survive the brutality of what the world has become. For this reason, they know it's best to be extremely wary about nearing the beaches of the Caribbean, for fear of the creature they simply but descriptively call The Snapper.
This creature, seemingly a blend of king crab and snapping turtle, is the product of any number of beneficial mutations which have arisen over an extremely long period of time, not the least of which are its extra - but by no means extraneous - heads. Each of these heads serves a specific and distinct purpose; each head closest to the gigantic, serrated pincers control these exclusively, and also do the bulk of the feeding for the creature as a whole. The centre head, though quite capable of consumption, is responsible primarily for the ambulation of the body. The medulla oblongata in each head is capable of sustaining the organic processes of the body independently. The end result of this redundancy is a creature which continues to be deadly at close quarters even with two heads damaged or destroyed.
No fewer than six feet long in adulthood, and - perhaps apocryphally - rumoured to grow up to ten feet long in some exceptional cases, the snapper roams coastal regions where large prey can be found, both above and below the water. Thoroughly amphibious, though still technically air-breathing, it is equally willing to scavenge as to kill its own prey when it happens upon something slow enough to fall within the reach of the snapper's massive claws and/or beaks, each of which are lined with sharp, gnashing spines which quickly eviscerate anything unlucky to find themselves being ground up between either.