Common slipper shell
The common slipper shell, Crepidula fornicata, has many other common names including common Atlantic slippersnail, boat shell, quarterdeck shell, fornicating slipper snail, and it is known in Britain as the "common slipper limpet". This is a species of medium-sized sea snail, a marine gastropod mollusc in the family Calyptraeidae, the slipper snails and cup and saucer snails.
This sea snail has an arched, rounded shell. On the inside of the shell there is a white "deck" which causes the shell to resemble a boat or a slipper, hence the common names. Some of these may be flat, slightly arched, or arched heavily. The 'Flat slipper shell' is also another type of slipper shell.
The species is considered an invasive species in Denmark, France, Italy, the Netherlands, Spain, and the UK, and has also spread to Norway and Sweden. It is known to damage oyster fisheries. It has also been introduced to the Pacific Northwest and Japan.
This is a common snail, found intertidally to a depth of 40 ft (12 m).
The species is a sequential hermaphrodite. The largest and oldest animals, at the base of a pile are female, the younger and smaller animals at the top are male. If the females in the stack die, the largest of the males will become a female.