Myosins are a large family of motor proteins found in eukaryotic tissues. They're responsible for actin-based motility. » "The term “myosin” was originally used to describe a group of similar, but nonidentical, ATPases found in striated and smooth muscle cells." From Pollard and Korn, 1973 Following the discovery, by Pollard and Korn, of enzymes with myosin-like function in Acanthamoeba castellanii, a large number of divergent myosin genes have been discovered throughout eukaryotes.… (More on Myosin)