California Semele Clam Shell, Semele californica

California Semele Clam Shell, Semele californica. Shell collected off the beach at Punta Chivato, Baja California Sur, April 2026. Size: 2.5 cm (1.0 inches) x 2.5 cm (1.0 inches) x 0.5 cm (0.2 inches). Photograph and Identifications courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

California Semele Clam Shell, Semele californica. Shell collected off the beach at Punta Chivato, Baja California Sur, April 2026. Size: 2.6 cm (1.0 inches) x 2.3 cm (0.9 inches) x 1.1 cm (0.4 inches). Photograph and Identifications courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Phylogeny: The California Semele Clam Shell, Semele californica (Reeve, 1853), is a bivalve mollusk in the Semelidae Family of Furrow Shells. The Semele Genus is one of fifteen genera in the Semelidae Family, and there are fifty-seven species in the Semele Genus. Semele was the mother of Dionysus in Greek mythology. They are known in Mexico  as Almeja California.

Morphology: California Semele Clam Shells have a subcircular to ovate outline and a moderately inflated profile. The right valve is slightly more inflated than the left. These shells are moderately heavy to heavy in construction. The anterior end is broadly rounded. The posterior may be broadly rounded or slightly truncate (appearing chopped off). California Semele Clam Shells are sculpted with wavy commarginal ribs, and radial striae. The exterior is white, often with pink or yellow blush. Some specimens have reddish maculations on the dorsal margin. The periostracum is thin and tan to brown in color. The interior is white, with a yellow, orange, or pink blush, especially near the ventral margin. California Semele Clam Shells reach a maximum of 4.4 cm (1.7 inches) in length.

Habitat and Distribution: California Semele Clam Shells are generally found in rubble or stones. They live from the intertidal zone to a depth of 70 m (230 feet). California Semele Clam Shells are a subtropical to tropical Eastern Pacific species. They have a limited range in Mexican waters. In the Gulf of California they are found as far north as Bahía San Luis Gonzaga. They are also found along the west coast of the Baja Peninsula from Bahía Santa María, Baja California Sur to Cabo San Lucas, Baja California Sur. They are absent along the Mexican mainland south of the Sea of Cortez.

Ecology and Behavior: California Semele Clam Shells are suspension feeders that feed primarily on plankton and suspended organic matter. In turn, they are prey for gastropods, sea stars, octopuses, rays, and crabs. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Their engagement in any type of commensal, parasitic, or mutualistic relationship has not been formally documented. From a conservation perspective they have not been formally evaluated. However, California Semele Clam Shells are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: Amphidesma californica and  Semele (Semele) californica.