This foot exerts a strong suction, adhering the keyhole limpet to its hard substratum. Keyhole limpet hemocyanin from "Megathura crenulata" is used as vaccine carrier protein. Another host is the keyhole limpet "Diodora aspera" where it lives in the gill groove. The keyhole limpet is also able to defend itself against attacks by starfish. This keyhole limpet is host to the ectoparasitic copepod "Anthessius nortoni". Keyhole limpet hemocyanin (KLH) and bovine serum albumin are two widely used carrier proteins. Keyhole limpet hemocyanin (KLH) is a copper containing respiratory protein, similar to hemoglobin in humans.