Pitted Donax Clam Shell, Donax punctatostriatus
Pitted Donax Clam Shell, Donax punctatostriatus. Size: 4.2 cm (1.7 inches) x 1.1 cm Shell collected from within the estuary of the Magdalena Bay complex, Baja California Sur, October 2018. Identification courtesy of Bob Hillis, Ivins, Utah.
Phylogeny: The Pitted Donax Clam Shell, Donax punctatostriatus (Hanley, 1843), is a bivalve mollusk that is a member of the Donacidae Family of Donax Clam Shells. The genus Donax is one of five genera in this family, and there are sixty-nine species in this genus. They are also known as the Pitted Bean Clam Shell and the Punctate Donax Shell and in Mexico as Coquina Punteada.
Description: The Pitted Donax Clam Shell is moderately inflated and has a trigonal profile. The anterior of the shell is long and rounded and the posterior end is truncate (appears chopped-off). The exterior of the shell is sculpted with fine radial ridges and when viewed under magnification, small linear pits (punctuations) can be seen between the ridges, especially at the shell’s ends. These pits are what gives the shell its common and scientific names. The interior margin is finely crenulate (serrated). The exterior of the shell is shiny white to tan in color, often with darker colored radial or concentric bands. The interior is white with purple wash or blotching, especially at the posterior end. Pitted Donax Clam Shells reach a maximum of 4.8 cm (1.9 inches) in length and 1.3 cm (0.5 inches) in height.
Habitat and Distribution: Pitted Donax Clams reside slightly buried beneath the surface of sand of exposed sandy beaches in the intertidal zone, and to depths up to 17 m (55 feet). Pitted Donax Clams are a subtropical to tropical Eastern Pacific species that are ENDEMIC to Mexican waters of the Pacific Ocean being found from Cedros Island, Baja California, south to Manzanillo, Colima, and throughout the Sea of Cortez.
Ecology and Behavior: Pitted Donax Clam Shells are suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are prey for crabs, fish, and shorebirds. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. They are known to host endoparasitic trematodes from the genus Postmonorchis. 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 relatively wide distribution and should be consider to be of Least Concern.
Synonyms: Donax (Chion) punctatostriatus, Donax punctatostriata, and Donax sowerbyi.