American slipper limpets look like slippers, therefore their name. They live off of plankton which they filter out of the seawater. They are often found piled one on top of another (up to twelve specimen), a real slipper limpet skyscraper. The snails at the top of the tower are always younger and male, the middle ones are in the process of changing sex and the lowest ones are older and female. American slipper limpets were imported during the previous century from North America, along with a load of oysters.