Cepoides Ark Shell, Anadara cepoides

Cepoides Ark Shell, Anadara cepoides. Size: 7.6 cm (3.0 inches) x 6.9 cm (2.7 inches). Shell collected off the beach at Km 26, Cero Colorado, Baja California Sur, March 2010. Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Cepoides Ark Shell, Anadara cepoides (Reeve, 1844), is a bivalve mollusk that is a member of the Arcidae Family of Ark Shells.  The genus Anadara is one of thirty-five genera in this family, and there are ninety-seven species in this genus. Ark shells obtain their name from their shell, which has alternating teeth along the hinge that allow the shell to close securely.

Description: The Cepoides Ark Shell is sturdy, with an almost oval outline. It has a broadly rounded anterior end and a chopped-off posterior end. The shell is inflated, with a prominent beak. The exterior of the shell is sculpted with 30 to 35 radial ribs and the interior margin of the shell is deeply grooved. The exterior is white in color and covered with a thin brown periostracum; the interior is white. Cepoides Ark Shells reach a maximum of 9.0 cm (3.5 inches) in length and 8.2 cm (3.2 inches) in height.

Habitat and Distribution: Cepoides Ark Shells are found within sandy substrates, at depths between 10 m (35 feet) and 84 m (275 feet). They are a tropical Eastern Pacific species. In Mexican waters they are found in the Gulf of California, from Gonzaga Bay, Baja California to Cabo San Lucas, Baja California Sur, and they range south along the mainland to Guatemala. They have not been documented from the West Coast of the Baja Peninsula.

Ecology and Behavior:  Cepoides Ark Shells are suspension feeders, which feed on plankton and suspended organic matter. They are prey for fish, crabs, sea stars, and gastropods. Cepoides Ark Shells are gonochoric and reproduce sexually, through broadcast spawning. There is no mention in the available literature of Cepoides Ark Shells engaging in any types of parasitic, commensal, or symbiotic relationships. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Arca cepoides.