Atlantic Slippersnail (or Slipper Limpet, Boat Shell, Quarterdeck)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Calyptraeidae, Genus: Crepidula, Species: Crepidula fornicata · Calyptraeidae (Slipper Limpet or Slipper Snail family) · Gastropod (Univalve); Cap-shaped/Patelliform. This specimen is a whole individual shell showing the exterior dorsal view.
Species
Crepidula fornicata
Shell Type
Gastropod (Univalve); Cap-shaped/Patelliform. This specimen is a whole individual shell showing the exterior dorsal view.
Family
Calyptraeidae (Slipper Limpet or Slipper Snail family)
Size
Approximately 1.0 to 1.25 inches (25-30mm). This is a mid-sized adult. The species typically ranges from 0.5 to 2.2 inches.
Color & Pattern
Overall slate gray to charcoal coloration. This specific dark gray/black hue is very common in Myrtle Beach specimens due to 'fossilization' or anaerobic burial in peat/mud layers, which stains the naturally cream-colored shell with minerals. Fine, concentric growth lines are visible, with some faint mottling beneath the mineral staining.
Rarity
Very Common. One of the most abundant shells found along the Carolinas, often appearing in large numbers after storms.
Habitat
Shallow marine waters and intertidal zones. They prefer hard substrates like rocks, other shells (often found stacked on one another), or horseshoe crab carapaces. Often found in estuaries and bays.
Geographic Range
Native to the Western Atlantic from Canada to the Gulf of Mexico. It has become a highly successful invasive species in Europe and the Pacific Northwest.
Description
An oval, boat-shaped shell with a low, slightly coiled apex shifted to one side. The exterior is relatively smooth but marked by fine concentric growth ridges. While the interior is not visible in this photo, it features a distinctive horizontal shelf (septum) that covers about half the opening, resembling a seat in a boat or the 'deck' of a ship. This dark-toned specimen shows the classic weathered 'low-country' aesthetic typical of South Carolina beach finds.
Key Features
Asymmetrical oval shape; low, posterior apex; smooth exterior with concentric rings; and the diagnostic internal 'shelf' (septum) found on the underside.
Collector Value
Minimal monetary value ($0.10-$0.50) due to extreme abundance. However, they are highly valued by craftspeople for jewelry and 'shell flowers' because of their unique internal shelf.
Condition Notes
Fair to Good. The shell is intact with no major chips, but the original lustrous finish and white/lavender interior colors are masked by heavy mineral staining and environmental erosion. This is a typical 'beach-worn' find.
Interesting Facts
This species is a sequential hermaphrodite; they often form stacks where the largest at the bottom is female and the smaller ones on top are male. If the female dies, the male above her will change sex to become the new female. They are also filter feeders, which is unusual for gastropods.
Ecological Role
Active filter feeders that help clear particulate matter from the water. They provide micro-habitats for other small organisms, though in high densities, they can compete with commercially important bivalves like oysters for food.
Similar Species
Crepidula convexa (Convex Slipper Shell) which is smaller and more inflated; Crepidula plana (Eastern White Slipper Shell) which is much flatter and stays white.
Beach Finding Tips
Look in the 'shell hash' piles at the high tide line in Myrtle Beach. They are often found attached to large whelk shells or inside the shells of dead horseshoe crabs.
Notes
Myrtle Beach SC