a slit
Note to the Nature of Wealth by John Ruskin

The orifice being not merely of a receptant, but of a suctional character. Among the types of human virtue and vice presented grotesquely by the lower animals, perhaps none is more curiously definite that that of avarice in the Cephalopod, a creature which has a purse for a body; a hawk's beak for a mouth; suckers for feet and hands; and whose house is its own skeleton.