Western White Slipper Shell, Crepidula perforans
Western White Slipper Shell, Crepidula perforans. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2025. Size: 3.7 cm (1.7 inches) x 2.4 cm (1.0 inch) x 0.6 cm (0.2 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Phylogeny: The Western White Slipper Shell, Crepidula perforans (Valenciennes, 1846), is a gastropod mollusk that is a member of the Calyptraeidae Family of Cup-and-Saucer and Slipper Shells. The Crepidula Genus is one of eleven genera in the Calyptraeidae Family, and there are forty-nine species in the Crepidula Genus. They are also known as known as the White Slipper Shell.
Description: The Western White Slipper Shell may have an irregular oval, elongate, or parrot-beak outline. The shape of the shell is somewhat determined by the shape of the surface they are attached to. The apex extends past the margin of the shell. The exterior is sculpted with commarginal growth ridges. Specimens from inside rock-boring clam holes have a foliated exterior. The internal “shelf” is set well below the shell’s margin and covers from about one quarter to one half of the aperture. The shelf has a lateral notch. The exterior color is white, with varying amounts of yellow to brown staining. The interior is shiny white. These shells have a thin periostracum. Western White Slipper Shells reach a maximum of 5.5 cm (2.2) inches in length.
Habitat and Distribution: Western White Slippers are found on rock, inside the aperture of large gastropods, and in the holes of rock-boring clams. They live in the lower intertidal zone, and to depths up to 8 m (25 feet). The Western White Slipper are a temperate to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from the south of Mazatlán, Sinaloa, along the central and southwest coasts of the mainland.
Ecology and Behavior: Western White Slippers are suspension feeders that feed primarily on planktonic algae, which they filter from the water by use of their gills. They are prey for fish, crabs, gastropods, and sea stars. Western White Slipper Shells are protandrous hermaphrodites, beginning life as males and later becoming females. They reproduce sexually, with internal fertilization. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formally documented. From a conservation perspective they have not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.
Synonyms: Crepidula explanata and Crepidula exuviata.