 Other bivalves , such as mussels , attach themselves to hard surfaces using tough byssus threads made of keratin and proteins . They are more exposed to attack by predators than the burrowing bivalves . Certain carnivorous gastropod snails such as whelks ( <unk> ) and murex snails ( <unk> ) feed on bivalves by boring into their shells , although many <unk> whelks ( e.g. , Busycon <unk> , Busycon <unk> ) are " chipping @-@ style " predators . The dog whelk ( <unk> <unk> ) drills a hole with its radula assisted by a shell @-@ dissolving secretion . The dog whelk then inserts its extendible proboscis and sucks out the body contents of the victim , which is typically a blue mussel . The whelk needs a few hours to penetrate the shell and thus living in the littoral zone is an advantage to the bivalve because the gastropod can attempt to bore through the shell only when the tide is in . 
