California Surfclam Shell, Mactrotoma californica

California Surfclam Shell, Mactrotoma californica. Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size: 6.3 cm (2.4 inches) x 4.2 cm (1.6 inches) x 0.8 cm (0.1 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny: The California Surfclam, Mactrotoma californica (Conrad, 1837), is a bivalve mollusk in the Mactridae Family of Surfclams. It is in the Mactrinae Subfamily. The Mactrotoma Genus is one of twenty-four genera in the Mactrinae Subfamily and the Mactrotoma Genus contains thirteen species. They are known in Mexico as Almeja California.

Description: California Surfclam Shells are trigonal to elongate in outline and moderately inflated in profile. These are of thin construction and are somewhat fragile. The valves are equilateral (equal in size and shape). The anterior end is rounded and the posterior is slightly truncate (appearing chopped off). The posterior is set off by a low ridge. These shells are sculpted with fine commarginal striae and some specimens have commarginal undulations at the beaks. The posterior gape is narrow. The hinge plate is long and narrow. The pallial sinus is shallow. California Surfclam Shells are whitish, with a dark brown periostracum. They reach a maximum of 6.5 cm (2.5 inches) in length.

Habitat and Distribution: California Surfclams are found buried in mud and muddy sand substrates in the intertidal zone, and to a depth of 30 m (98 feet). They a a subtropical to tropical Eastern Pacific species. In Mexican waters they are found along the entire Pacific coast, including the Gulf of California.

Ecology and Behavior:  California Surfclams are suspension feeders that feed primarily on plankton and other suspended organic matter. Their predators include birds, crabs, carnivorous mollusks, sea stars, and fish. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae. Their commensal, parasitic, or symbiotic relationships have not been formally documented. From a conservation perspective California Surfclam Shells have not been formally evaluated. However, they are fairly common with a wide distribution and should be consider to be of Least Concern.

Synonyms: Mactra californica and Mactrella californica.