 Many bivalves have no eyes , but a few members of the <unk> , <unk> , <unk> , <unk> , <unk> , and <unk> 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 . 
