Common Atlantic Slippersnail

Crepidula fornicata

The common slipper shell is a species of medium-sized sea snail, a marine gastropod mollusc in the family Calyptraeidae, the slipper snails and cup and saucer snails.
Fornicating Slipper Snail - Crepidula fornicata Common slipper shells start their lives as males, but some change to females as they grow older. The change is initiated by a waterborne hormone that regulates the female characteristics. Once they change into females, they remain females. To make reproduction more convenient, they often stack up on top of each other with the larger females on the bottom, the smaller males on top, and the hermaphrodites in the middle. If the ratio of males to females gets too high, the male reproductive organs will degenerate and the animal will become female.

Habitat: Tidal pool during low tide Common slipper shell,Crepidula,Crepidula fornicata,Geotagged,Summer,United States,slipper shell,slipper snail,snail

Appearance

The size of the shell is 20–50 mm. The maximum recorded shell length is 56 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.
Common slipper shell - Crepidula fornicata Spotted on a rock in the intertidal zone. I didn't get a shot of the underside because they firmly clamp themselves to rocks and forcefully removing them can injure them. Common slipper shell,Crepidula fornicata,Geotagged,Spring

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 from as far north as Nova Scotia to as far south as the Gulf of Mexico. It has been introduced accidentally to other parts of the world and has become problematic.It was introduced to the state of Washington.
The species was, however, brought to Europe together with the eastern oyster "Crassostrea virginica". In Belgium, the first slipper limpet was found on September 28, 1911, attached to an oyster in Ostend, and since the 1930s it is seen as a common species along the Belgian coast.

The species is considered an invasive species in Denmark, France, Italy, the Netherlands, Spain, and the United Kingdom, and has also spread to Norway and Sweden. 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. A continued expansion to the north is probably inhibited by temperature: low temperatures during the winter can slow down or inhibit the development of the slipper limpet. It has also been introduced to the Pacific Northwest and Japan.
Coralline Algae on Common Slipper Shells (Crepidula fornicata) Red, calcareous algae growing on a stack of 3 slipper shells

Habitat: Low tide zone Common slipper shell,Crepidula fornicata,Geotagged,Spring,United Statesred algae,calcareous red algae,coralline algae,encrusting red algae

Behavior

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.
Slippersnail - Crepidula fornicata Habitat: Intertidal zone Common Atlantic Slippersnail,Crepidula,Crepidula fornicata,Geotagged,Spring,United States,slippersnail

Habitat

This is a common snail, usually found intertidally, infralittoral and circalittoral and in estuaries.

Minimum recorded depth is 0 m. Maximum recorded depth is 70 m.

They are often found, sometimes living stacked on top of one another, on rocks, on horseshoe crabs, shells and on dock pilings.
Slipper limpet on a blue crab Crepidula fornicata attached to Callinectes sapidus at Barrington Beach in Rhode Island. Common slipper shell,Crab,Crepidula fornicata,Limpet,Shell

Food

Generally for Calyptraeidae, feeding habits include planktonic and minute detrital food items through either suspension or deposit feeding.

References:

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Taxonomy
KingdomAnimalia
DivisionMollusca
ClassGastropoda
OrderLittorinimorpha
FamilyCalyptraeidae
GenusCrepidula
SpeciesC. fornicata