Atlantic Slipper Snail       Crepidula fornicata



Look closely at the clump of shells, left of the fingers, attached to the oyster shell.  Notice that there are approximately five shells stacked one upon another.  This is not a random occurrence, but rather a sensible way for sedentary, filter feeders to ensure the next generation of slipper shells.  The smallest, topmost snails are males while the larger snails at the bottom are female.  As they grow older and larger the males can turn into females.  Stacks of slipper snails up to 14 individuals high have been found.  They are attached to one another and the substrate by shell projections or by a calcarious secretion from the foot.  Slipper snails can be found on hard surfaces in the low intertidal and shallow subtidal zones.


The Atlantic slipper snail can grow to 1.5 inches long.  This species was accidentally introduced to Puget Sound when oysters from the Atlantic Ocean were brought here many years ago. There are several other native slipper snails in the area whose shell apex differs from the Atlantic species and are smaller.


Like a limpet snail they have an untwisted shell, but the top of the shell is flopped over.  Inside, their anatomy is unusual, having a shelf extending in from the margin of the shell.  As a result an upside down, empty shell looks like a slipper - hence the name.  In addition, unlike other snails, they use mucus on their gills to strain out food from the water rather than using a rasp-like tongue to scrape algae.