The rough keyhole limpet (Diodora aspera) uses the hole at the top of its shell as part of the respiration process. Fresh oxygenated water is drawn under the shell and over the gills, while the waste water is expelled from this top opening. This creates a flow of clean water through the animal. For defense, this limpet can extend its mantle upward covering the shell margin to provide protection from sea stars. The rough keyhole limpet grows to about three inches (7.6 cm) long, with a range from northern Alaska to Nicaragua.