ON PREDATOR DETERRENCE BY PRONOUNCED SHELL ORNAMENT IN EPIFAUNAL BIVALVES

Laboratory experiments, undertaken to determine the effectiveness of p ronounced shell ornament in epifaunal bivalves against predatory shell boring by subtropical muricid gastropods and extraoral feeding by ast eroids, suggest that natural and artificial spines deter muricid preda tors from attacking ornamented areas of the bivalve shell but do not h ave a similar effect upon predatory asteroids. These findings are disc ussed in relation to the extant and often highly spinose cementing biv alve families Spondylidae and Chamidae. The adaptive radiation of the Muricidae in the Albian may have resulted in selection for highly orna mented epifaunal bivalve taxa in shallow, warm water environments wher e 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 Pala eozoic. It is concluded that the pronounced shell ornament of the free valves of warm water cemented epifaunal bivalve taxa is functional ag ainst shell boring muricids. Other hypothesized functions are discusse d briefly.