The rough keyhole limpet is the only keyhole limpet found on the intertidal beaches of northwestern Washington today. It lives in the low intertidal to subtidal of rocky shorelines. As its name implies, it has a small oval opening at the top of its short, conical shell. Although the keyhole limpet superficially resembles "true" limpets, its soft anatomy reveals an important difference. True limpets draw water into their mantle cavity on the left side, pass it over a single gill and discharge it on the right side. Keyhole limpets draw water in both sides, where it flows over paired gills before flowing out through the "keyhole" aperture at the peak of the shell.