Pacific Spiny Cockle Shell, Dallocardia quadragenaria

Pacific Spiny Cockle Shell, Dallocardia quadragenaria. Shell collected from Coronado Islands, Baja California, October 2022. Size:  11.0 cm (4.3 inches) x 8.3 cm (3.3 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Pacific Spiny Cockle, Dallocardia quadragenaria (Conrad, 1837), is a bivalve mollusk that is a member of the  Cardiidae Family of Cockles and True Cockles. The genus Dallocardia is one of forty-nine genera in this family, and there are four species in this genus. They have many common names including the Giant Pacific Cockle, the Spiny Pricklycockle, and the Spiny Cockle (Pacific).

Description: The Pacific Spiny Cockle shell is very inflated with a rounded quadrilateral profile. Both ends are well rounded, with the posterior slightly flattened. The exterior has approximately 40 radiating ribs, which extend to the margins, causing the margins to be scalloped. The ribs are sculpted with small, sharp, tubercles. These shells are yellowish to brownish in color. The inside is white, with orange at the margins. Pacific Spiny Cockles are large bivalves, reaching a maximum of 13 cm (5.1 inches) in length and 12 cm (4.7 inches) in height.

Habitat and Distribution: The Pacific Spiny Cockle is found within bays and on sandy substrates offshore. They are found intertidally, and to a depths up to 40 m (135 feet).  They are a temperate to subtropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean on a limited basis being found along the central and northern coasts of the Baja Peninsula north of Magdalena Bay, Baja California Sur. They have not been documented from the Sea of Cortez, where they are replaced by the similar looking Panama Thorny Cockle Shell, Dallocardia radula.

Ecology and Behavior: Pacific Spiny Cockles are suspension feeders that feed primarily on plankton and other suspended organic matter. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization.  There is no mention in the available literature of them 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: Cardium arenatum, Cardium luteolabrum, Cardium quadragenarium, and Trachycardium quadrgenarium.