Bicolored Semele Clam Shell, Semele bicolor

Bicolored Semele Clam Shell, Semele bicolor. Shell collected off the beach at Punta Chivato, Baja California Sur, March 2026. Size: 2.5 cm (1.0 inches) x 2.2 cm (0.9 inches) x 0.5 cm (0.2 inches). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Phylogeny: The Bicolored Semele Clam Shell, Semele bicolor (C. B. Adams, 1852), 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 Bicolor.

Morphology: Bicolored Semele Shells have a circular outline and a moderately inflated profile. The shells are thinly constructed compared to most other species in this genus. The anterior end is longer than the posterior, and is broadly rounded. The posterior may be broadly rounded or slightly truncate (appearing chopped off). Bicolored Semele Shells are sculpted with commarginal growth lines and radial striae. The exterior is white with purple or orange umbones (curved region above beaks). Some specimens have tan maculations posteriorly. The periostracum is thin and clear.  The interior is white, with a purple blush. Bicolored Semele Shells reach a maximum of 3.1 cm (1.2 inches) in length.

Habitat and Distribution: Bicolored Semele Clams are found on sand and mud substrates in the intertidal zone, and to a depth of 27 m (89 feet). Bicolored Semele Shells are a subtropical to tropical Eastern Pacific species. They are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Bahía Willard, Baja California, in the Sea of Cortez, and from along the west coast of the Baja Peninsula.

Ecology and Behavior: Bicolored Semele Clams are suspension feeders that feed primarily on plankton and suspended organic matter. In turn, they are prey for gastropods, sea stars, octopuses, 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, the Bicolored Semele Clams are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: Amphidesma bicolor, Amphidesma pulchella, Semele (Semele) bicolor, and Semele fucata.