Slipper Snail (also known as Boat Shell, Quarterdeck Shell, or Fornicating Slipper Snail)
Phylum: Mollusca, Class: Gastropoda, Order: Littorinimorpha, Family: Calyptraeidae, Genus: Crepidula, Species: C. fornicata · Calyptraeidae (Slipper Snail or Cup-and-saucer family) · Gastropod (univalve) with a cap-like, oval shape featuring an internal deck-like shelf.
Species
Crepidula fornicata
Shell Type
Gastropod (univalve) with a cap-like, oval shape featuring an internal deck-like shelf.
Family
Calyptraeidae (Slipper Snail or Cup-and-saucer family)
Size
Based on the image, approximately 1 to 1.5 inches in length. This is a common size for mature adults, which typically range from 0.75 to 2 inches.
Color & Pattern
External color is a mottled grayish-white with faint brownish streaks and speckles. The interior exhibits a glossy, porcelaneous finish with a distinctive tan or chestnut-brown muscle scar and a white 'deck' or septum.
Rarity
Very Common
Habitat
Found in marine environments, specifically intertidal and shallow subtidal zones. They prefer hard substrates including rocks, empty shells (often whelk shells), and the shells of living horseshoe crabs and oysters.
Geographic Range
Native to the Western Atlantic (Canada to Gulf of Mexico). Widely introduced and now invasive in Europe, the Mediterranean, and the Pacific coast of North America.
Description
An oval, convex gastropod shell that lacks a traditional spiral spire. The apex is turned to one side and situated at the posterior end. The most striking feature is the internal translucent white shelf (septum) that covers roughly half of the shell's aperture, creating a boat-like appearance.
Key Features
Cap-shaped shell; diagnostic internal 'deck' or shelf; apex shifted toward the posterior edge; often found with curved edges from being stacked on top of other shells.
Collector Value
Minimal financial value (less than $1 USD) due to extreme abundance. They are primarily valued by beginning collectors for their unique 'boat' shape or as educational specimens for studying invasive species.
Condition Notes
Beach-worn condition with visible erosion along the margins. The internal septum is slightly chipped but mostly intact. Color shows some fading due to sun exposure. Grade: Fair/Good.
Interesting Facts
This species is a protandrous hermaphrodite, meaning they start life as males and change to females as they age. They are often found in 'breeding stacks' where the larger, older females are at the bottom and smaller males are at the top.
Ecological Role
Filter feeders that can become a nuisance in oyster beds by competing for food and space. They serve as a food source for sea stars and various predatory snails.
Similar Species
Crepidula plana (Eastern White Slipper Snail), which is much flatter and purely white, and Crepidula convexa (Convex Slipper Snail), which is smaller and more deeply arched.
Beach Finding Tips
Look along the high tide line among shell hash or attached to oyster clusters. They are particularly abundant after storms that dislodge them from submerged substrates.