Atlantic Slipper Shell (also known as common slipper snail or boat shell)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Calyptraeidae, Genus: Crepidula, Species: Crepidula fornicata · Calyptraeidae (Slipper snail family) · Gastropod, whole shell, cap-shaped or slipper-shaped form
Species
Crepidula fornicata
Shell Type
Gastropod, whole shell, cap-shaped or slipper-shaped form
Family
Calyptraeidae (Slipper snail family)
Size
Approximately 0.5 inches (12 mm), which is quite small and likely a juvenile or male. Adults typically range from 1 to 2 inches (25-50 mm).
Color & Pattern
Purplish-brown base with darker brown radial streaks and mottling. The interior features a white, glossy porcelain-like shelf (septum) covering the posterior half. Colors appear natural and slightly weathered.
Rarity
Very Common
Habitat
Marine environment, typically found attached to hard substrates, rocks, other shells, or horseshoe crabs in intertidal to shallow subtidal zones down to about 60 meters.
Geographic Range
Native to the Western Atlantic from Nova Scotia to the Gulf of Mexico and the Caribbean. Introduced and widely established in Europe and parts of the Pacific.
Description
A small, cap-shaped marine snail shell with an arched, oval profile resembling a tiny boat or slipper. The apex is curved and turned to one side. The exterior shows delicate growth lines and brownish patterns, while the interior is characterized by a distinctive white, horizontal deck-like shelf across the back half, which gives the species its common name.
Key Features
Cap-shaped exterior with an off-center turned apex, paired with a distinctive internal white shelf (septum) that covers roughly half of the aperture.
Collector Value
Very low commercial value due to high abundance, but a staple educational specimen for beginner shell collections.
Condition Notes
Good overall condition for a beach-worn specimen. Intact with minor natural wear on the exterior, retaining its characteristic internal deck and a pleasant purple-brown coloration. Collectibility grade: Good.
Interesting Facts
Atlantic slipper shells are protandrous hermaphrodites, meaning they are all born male and later develop into females. They pile on top of one another in stacks, where the bottom ones are large females and the top ones are smaller males.
Ecological Role
Suspension feeders that filter phytoplankton from the water column. They can form dense aggregations that alter benthic habitats, and they are sometimes considered an invasive pest in oyster fisheries outside their native range.
Similar Species
Crepidula plana (Eastern White Slipper Shell), which is flatter and typically white, and Crepidula convexa (Convex Slipper Shell), which is much smaller and more heavily arched.
Beach Finding Tips
Look along drift lines on sandy and shelly beaches of the US Atlantic coast, or inspect washed-up larger shells, whelks, and horseshoe crabs where they frequently attach.
Notes
Us Atlantic coast