seasnail: any of several creeping marine gastropods with a spirally coiled shell: whelks; tritons; moon shells; neritids
gastropod: a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes
histocompatibility complex: a family of fifty or more genes on the sixth human chromosome that code for proteins on the surfaces of cells and that play a role in the immune response