|Shooting outside, daylight, without character.nA shell is the external skeleton of a mollusk. The majority of mollusks with shell are in the class of gastropods as snails, and in that of bivalves as oysters. Three other classes of mollusks secrete systematically a shell: scaphopodes dental consonants, polyplacophores chitons and monoplacophores. It is also the case for almost all of cephalopods, even if she is sometimes reduced and covered by the coat `bone` of the cuttlefishes or `feather` of squids. She It is absent at the adult`s only in a rather small number of cases: certain slugs, most of the opisthobranches, certain pieuvres, as well as two groups of atypical mollusks, solénogastres and caudofovéates, formerly grouped included for that reason in the class of aplacophores. One subdivision of the malacology, the study of mollusks, conchyliology, is dedicated to the study of mollusks with shell.