Laboratory experiments, undertaken to determine the effectiveness of pronounced shell ornament in epifaunal bivalves against predatory shell boring by subtropical muricid gastropods and extraoral feeding by asteroids, suggest that natural and artificial spines deter muricid predators from attacking ornamented areas of the bivalve shell but do not have a similar effect upon predatory asteroids. These findings are discussed in relation to the extant and often highly spinose cementing bivalve families Spondylidae and Chamidae. The adaptive radiation of the Muricidae in the Albian may have resulted in selection for highly ornamented epifaunal bivalve taxa in shallow, warm water environments where the epifaunal habit renders sessile prey particularly vulnerable to attack by roving durivorous predators. The ability to produce spines, however, was already apparent in ancestral Pectinoida in the late Palaeozoic. It is concluded that the pronounced shell ornament of the free valves of warm water cemented epifaunal bivalve taxa is functional against shell boring muricids. Other hypothesized functions are discussed briefly.