Common Slipper Shell, Boat Shell, Quarterdeck
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Calyptraeidae, Genus: Crepidula, Species: fornicata · Calyptraeidae (Slipper or Cup-and-saucer snail family) · Gastropod (univalve); Cap-shaped/Oval with an internal horizontal shelf.
Species
Crepidula fornicata
Shell Type
Gastropod (univalve); Cap-shaped/Oval with an internal horizontal shelf.
Family
Calyptraeidae (Slipper or Cup-and-saucer snail family)
Size
Approximately 1 inch (2.5 cm) in length. This is an average adult size; species typically range from 0.5 to 2 inches.
Color & Pattern
Base color is a dull cream to light tan with faint reddish-brown mottling and streaks. The exterior appears naturally weathered and slightly sun-bleached. The interior (though mostly hidden) typically shows a polished, white shelf and a brownish interior wall.
Rarity
Very Common. This is one of the most frequently found shells on the East Coast of the United States.
Habitat
Marine; found in intertidal and shallow subtidal waters. They prefer firm substrates like rocks, other shells, or horseshoe crabs, often stacking on top of one another.
Geographic Range
Native to the Western Atlantic from Canada to the Gulf of Mexico. Highly common in North Carolina waters including Holden Beach.
Description
An oval, convex gastropod shell that lacks the typical spiral whorls of most snails. The exterior is characterized by rough growth lines and a slightly hooked apex turned to one side. The most distinctive feature, found on the underside, is a porcelain-like horizontal platform (the shelf) that covers roughly half the aperture, giving it the appearance of a tiny slipper or a boat with a deck.
Key Features
The internal 'deck' or shelf; the asymmetrical, low-profile cap shape; and the tendency for the shell apex to be turned to the posterior end.
Collector Value
Low monetary value due to extreme abundance. However, they are highly desirable for craftspeople and beginning collectors due to their unique 'slipper' shape. A 'stack' of shells preserved together is considered a more valuable natural history specimen.
Condition Notes
Fair to Good. The shell shows significant beach-wear (abrasion) which has smoothed the finer sculptural details and edges. There is no periostracum remaining, and the color is slightly faded from exposure to surf and sun.
Interesting Facts
These mollusks are sequential hermaphrodites; they start life as males and turn into females as they grow larger. They often live in 'stacks' where the large female is at the bottom and smaller males are stacked on top of her.
Ecological Role
Filter feeders that clean the water column of plankton. They serve as a food source for oyster drills, sea stars, and crabs. In some areas outside their native range, they are considered a problematic invasive species.
Similar Species
Crepidula convexa (Convex Slipper Shell) which is much smaller and more deeply curved, and Crepidula plana (Eastern White Slipper Shell) which is very flat and pure white.
Beach Finding Tips
Look in the 'shell hash' lines at low tide. Because they are light and cup-shaped, they often wash up in large numbers after storms. At Holden Beach, look near the waterline where debris accumulates.
Notes
Holden Beach, NC