Colus gracilisColus gracilis is a species of sea snail, a marine gastropod mollusk in the family Buccinidae, the true whelks and the like.DescriptionA smooth form with flatter whorls, 40 to 100 mm in length, but a highly variable species that occurs in several morphologically different geographical and bathymetrical forms; these forms may look identical over large areas, then give an impression that several near species are involved.