 Many bivalves have no eyes , but a few members of the Arcoidea , Limopsoidea , Mytiloidea , Anomioidea , Ostreoidea , and Limoidea have simple eyes on the margin of the mantle . These consist of a pit of photosensory cells and a lens . Scallops have more complex eyes with a lens , a two @-@ layered retina , and a concave mirror . All bivalves have light @-@ sensitive cells that can detect a shadow falling over the animal . 
