Monoplacophora, meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell now living at the bottom of the deep sea. Extant representatives were not recognized as such until 1952; previously they were known only from the fossil record. Although the shell of many monoplacophorans is limpet-like in shape, they are not gastropods and are not closely related to gastropods.