seasnail - any of several creeping marine gastropods with a spirally coiled shell: whelks; tritons; moon shells; neritidsgastropod, univalve - a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes whelk - large carnivorous marine gastropods of coastal waters and intertidal regions having a strong snail-like shell triton - tropical marine gastropods having beautifully colored spiral shells limpet - any of various usually marine gastropods with low conical shells; found clinging to rocks in littoral areas |