Common Slipper Shell (Crepidula fornicata)
Alternate common names: Slipper Shell, Lady's
Color: The exterior of the shell is dull white or cream with wavy longitudinal lines of a light chestnut color. The interior is a shiny light brown.
Size: Up to 1 1/2 inches wide, 2 1/2 inches long.
Habitat: Coastal marshes and inlets, tidal pools, and beaches.
Seasonal appearance: All year.
The common slipper shell is one of the more common shells found along the Rhode Island coast. This shell is shaped like an egg or oval that has been cut in half with the top of the shell turned sharply to one side. Looking at the underside of the shell, it is easy to see how it got its name. Underneath the shell is a ledge to support the internal organs; this ledge extends about half the length of the animal. Different slipper shell species are characterized by different shell textures, including rough, smooth, ribbed, corrugated, and flat. Although they have a foot for locomotion, by the time they reach maturity they anchor themselves to a hard substrate and remain stationary.
Life History and Behavior
All common slipper shells start their lives as males, but some change to females as they grow older. A waterborne hormone regulates the female characteristics. Once they change into females, they remain females. They often stack up on top of each other for convenient reproduction. The larger females are on the bottom, the smaller males are on the top, and the hermaphrodites are between the two. If the ratio of males to females gets too high, the male reproductive organs will degenerate and the animal will become female. Eggs are laid in thin-walled capsules that the female broods under her foot.
Common slipper shells also form stacked aggregations when there is no hard substrate on which to attach. They attach to objects in large numbers and can sometimes suffocate the animal on which they are attached. Common slipper shells use their cilia to create water currents that flow through their mantle cavity. They are filter feeders, and as the water passes through the cavity, mucous-covered gills trap various types of phytoplankton and algae. The common slipper shell then uses its radula to remove the food and bring it to its mouth.
Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.