Crepidula fornicata

The size of the shell is 20–50 mm. 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. There is variability in the shape of the shell: some shells are more arched than others. Groups of individuals are often found heaped up and fastened together, with the larger, older females below and the smaller, younger males on top. As a heap grows, the males turn into females (making them sequential hermaphrodites). ==Distribution==

The species is native to the western Atlantic Ocean, specifically the Eastern coast of North America. Its distribution ranges from 48°N to 25°N; 97.2°W to 25°W It is known to damage oyster fisheries. The slipper limpet has few to no predators in Europe, and can thrive on several types of hard bottoms and shellfish banks. ==Human consumption==

Culinary use Although considered an invasive species, there are attempts to harvest and market the snail in France. ==Ecology==

Habitat Although Crepidula fornicata is a species with cosmopolitan distribution, and can tolerate a wide range of environmental conditions, populations are particularly well developed in wave protected areas such as bays, estuaries or sheltered sides of wave exposed islands. Their distribution within the water column has been shown to a minimum of 0m and a maximum of 70m. They are often found living stacked on top of one another on rocks, on horseshoe crabs, shells and on dock pilings. Feeding habits Generally for Calyptraeidae, feeding habits include planktonic and minute detrital food items through either suspension or deposit feeding. Life cycle & reproduction The species is a sequential hermaphrodite. The slipper limpet normally lives in stacks of up to 12 individuals, with the largest at the bottom and with increasingly smaller individuals stacked on top of one another. 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. Breeding can occur between February and October with peak activity occurring in May and June. Roughly 80-90% of females spawn during May and June. Most slipper limpet females will spawn twice in a year, generally after neap tides. As an invasive non-native species Within The United Kingdom, the common slipper limpet is considered to be an invasive non-native species (INNS). The release of slipper limpets to the sea is an offence within England. This species has been recorded around the coasts of Southern England and Wales as far north as Anglesey on the west coast and Spurn Point on the east coast. The slipper limpet has been recorded within the Thames Estuary amongst other brackish environments. First recorded in 1872, these non-native limpets arrived in England and Wales from America in a shipment of oysters. Their impacts to U.K ecosystems are still being investigated, however, there is growing evidence that this species is detrimental to native molluscs beds such as Queen scallop Aequipecten opercularis, Edible oyster Ostrea edulis, and Blue mussel Mytilus edulis. Common slipper limpets are currently being considered as a food source in efforts to reduce their spread from Southern England. ==References==