Pacific Half-Slipper Shell (White Slipper Snail, Boat Shell)
Kingdom: Animalia; Phylum: Mollusca; Class: Gastropoda; Order: Littorinimorpha; Family: Calyptraeidae; Genus: Crepidula; Species: C. excavata · Calyptraeidae (Slipper Snail or Cup-and-Saucer family) · Gastropod (univalve); Cap-shaped/Limpet-like shell; Whole shell (dorsal view visible)
Species
Crepidula cf. excavata (Confidence: 85%)
Shell Type
Gastropod (univalve); Cap-shaped/Limpet-like shell; Whole shell (dorsal view visible)
Family
Calyptraeidae (Slipper Snail or Cup-and-Saucer family)
Size
Approximately 15-20mm in length. This is within the typical range for the genus, which usually measures 10-30mm.
Color & Pattern
Creamy white to tan base color with light brownish mottling near the apex. The surface shows fine concentric growth lines. The color appears naturally weathered and slightly sun-bleached, which is common for beach-found specimens.
Rarity
Common (found regularly on beaches in the Panamic province)
Habitat
Found in marine environments, specifically intertidal and shallow subtidal zones. They prefer sticking to hard substrates such as rocks, other shells (including living snails and crabs), and debris.
Geographic Range
Eastern Pacific Ocean, specifically from the Gulf of California (Cabo San Lucas area) down to Peru.
Description
An oval, cap-shaped shell with a low, eccentric apex that is slightly curled to the side. The exterior is relatively smooth compared to Atlantic species, though it exhibits subtle radiating striae and concentric growth rings. The interior (unseen in photo) contains a characteristic horizontal shelf or 'deck' that covers half of the aperture.
Key Features
The distinctive slipper/boat shape, the off-center apex located near the posterior margin, and the hidden internal transverse septum (the 'deck').
Collector Value
Minimal financial value ($1-$3 USD); however, it is a high-interest item for educational collections and beachcombers due to its unique 'slipper' anatomy.
Condition Notes
Fair to Good; the shell shows clear signs of beach-wear and environmental erosion, which has smoothed the finer sculptural details. There are no visible major cracks, making it a decent educational specimen.
Interesting Facts
Slipper shells are sequential hermaphrodites; they start life as males and turn into females as they grow larger. They often live in 'stacks' where the larger females are at the bottom and smaller males are on top.
Ecological Role
Suspension feeders that filter phytoplankton from the water column. They provide substrate for other small organisms and serve as a food source for predatory snails and crabs.
Similar Species
Crepidula fornicata (Atlantic Slipper, larger and more robust) and Crepidula onyx (Onyx Slipper, usually darker/brownish).
Beach Finding Tips
Look in drift lines at low tide, especially after a storm. They are often found washed up still attached to broken pieces of larger shells like clams or scallops.
Notes
Cabo