Megathura crenulata Sowerby, 1825 by Scuba diving at 35’ on side of large rock pinnacle, Monterey, California

Keyhole limpets are a primitive type of gastropod that live fastened on rocks. They have a slimy grey skin that covers the shell and have a central hole which is used to expel waste away from the gills and mouth. Limpets feed off of algae with a radula that scrapes the algae into their mouths. By using the muscular foot, the limpets are able to form such a tight bond to their home rocks that it makes it very dif cult to pry them off, offering protection against predators and collectors. The at shell protects it from crashing waves and coastal currents.

Megathura crenulata Sowerby, 1825, known at the Giant Keyhole Limpet, is found on the west coast of California in temperate waters. In the past, keyhole limpet shells were used as currency and decoration by Native Americans. This shell, about 4.5″ in size, was donated by Richard Kent.