Acanthopleura granulata, the West Indian fuzzy chiton.
Monroe county, Florida (13 March 2021).
While these may look sort of like fossils, these are living West Indian fuzzy chitons, a species of specialized mollusk that latches onto rocky surfaces and sports a mineralized outer shell. They primarily feed on algae at night. If you ever find yourself in the Florida Keys, carefully explore some of those limestone shorelines. You may find some chitons hidden in plain sight!