Atlantic Petricolid Shell, Choristodon robustus
Atlantic Petricolid Shell, Choristodon robustus. Shell collected off the beach at Punta Chivato, Baja California Sur, May 2022. Size: 2.5 cm (1.0 inches) x 2.7 cm (1.1 inches) x 0.8 cm (0.3 inches). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.
Phylogeny: The Atlantic Petricolid, Choristodon robustus (G. B. Sowerby I, 1834), is a bivalve mollusk in the Veneridae Family of Venus Clam Shells. The Choristodon Genus is one of one hundred and seven genera in the Veneridae Family, and there are three species in the Choristodon Genus. They are also known as the Robust Petricolid Shell.
Description: Atlantic Petricolid Shells have a trigonal to ovate outline and an inflated profile. The anterior is shorter and broadly rounded. The posterior end is truncate (appearing chopped-off). In some specimens the right valve is larger than, and overgrows, the left valve. These shells are moderately thin in construction. The exterior is sculpted with around fifty narrow radial ribs, and fine commarginal striae. The ribs are farther apart, and more pronounced, posteriorly. The inside is smooth and the pallial sinus moderately deep and broadly rounded. The exterior is white to tan in color. The interior is white to tan, often with brownish-purple or purple blotches, especially posteriorly. Atlantic Petricolid Shells reach a maximum of 4.3 cm (1.7 inches) in length.
Habitat and Distribution: Atlantic Petricolids are found in burrows in coral, large shells, and limestone rock. They use the ridges on their shell to dig their burrows. They live in the intertidal zone, and to depths of 55 m (180 feet). Atlantic Petricolid Shells are a subtropical to tropical Atlantic and Eastern Pacific species. Atlantic Petricolid Shells are found in all Mexican waters of the Pacific Ocean with the exceptions that they are absent from the west coast of the Baja Peninsula, north of Laguna Ojo de Liebre ( Scammon’s Lagoon). They are found in all Mexican waters of the Gulf of Mexico, possibly extending into the Caribbean. Some sources limit the distribution of this species to the Atlantic Ocean and state that the Eastern Pacific specimens belong to a new species. So far, there is no description or valid name for this new species.
Ecology and Behavior: Atlantic Petricolid Shells are suspension feeders, which feed on plankton and suspended organic matter. They are prey for fish, crabs, shorebirds and gastropods. Atlantic Petricolid Shells are gonochoric and reproduce sexually, through broadcast spawning. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formally documented. From a conservation perspective they have not been formally evaluated. However, they are fairly common with a wide distribution and should be consider to be of Least Concern.
Synonyms: Choristodon robustum, Petricola anachoreta, Petricola bulbosa, Petricola buwaldi, Petricola robusta, Petricola robusta, Petricola sinuosa, and Petricola venusta.