Wikipedia
Calyptraeidae
The Calyptraeidae, the slipper snails or slipper limpets, cup-and-saucer snails, and Chinese hat snails, are a family of small to medium-sized marine prosobranch gastropods. This family includes the slipper snails ( Crepidula species), the Chinese hat snails, ( Calyptraea species), and the cup-and-saucer snails ( Crucibulum species) among others.
The Calyptraeidae are the only family in the superfamily Calyptraeoidea. This family has no subfamilies according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005.
Crepidula fornicata was brought to Europe on imported American oysters in the late 19th century and is now considered a significant pest in European oyster beds.