Pallid Dwarf Mactra Shell, Mulinia pallida

Pallid Dwarf Mactra Shell, Mulinia pallida. Shell collected off the beach at San Juanico, Baja California Sur, May 2000. Size: 5.4 cm (2.1 inches) x 4.4 cm (1.7 inches) x 1.6 cm (0.6 inches). Photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Pallid Dwarf Mactra Shell, Mulinia pallida. Shell collected off the beach at Punta Chivato, Baja California Sur, May 2023. Size: 5.7 cm (2.2 inches) x 4.5 cm (1.8 inches) x 1.7 cm (0.7 inches). Photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Phylogeny: The Pallid Dwarf Mactra Shell, Mulinia pallida (Broderip and G.B. Sowerby I, 1829), is a bivalve mollusk in the Mactridae Family of Surfclam Shells and the Mactrinae Subfamily. The Mulinia Genus is one twenty-four genera in the Mactrinae Subfamily, and contains ten species. They are known in Mexico as the Almeja Pálida.

Description: Pallid Dwarf Mactra Shells are trigonal in outline. The posterior end is slightly longer than the anterior. They are of thin construction and may be moderately to highly inflated. The anterior end is sharply rounded and the posterior is pointed. The posterior slope is set off from the central slope by a sharp angle. The umbones are large, and projecting in larger specimens. These shells are sculpted with commarginal striae. The interior has a smooth ventral margin. The resilifer (internal ligament attachment process) protrudes ventrally from the hinge plate. Pallid Dwarf Mactra Shells are cream colored with a yellow to brown periostracum.  The periostracum may be fringed in smaller, less-worn, specimens. They reach a maximum of 9.3 cm (3.6 inches) in length.

Habitat and Distribution: Pallid Dwarf Mactra Shells are found buried in mud and muddy sand substrates in the intertidal zone, and to a depth of 48 m (157 feet). They favor protected waters such as bays and lagoon, and are often associated with mangroves. They are a subtropical to tropical Eastern Pacific species that is found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Punta Pequeña, Baja California Sur, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior:  Pallid Dwarf Mactra Shells are suspension feeders that feed primarily on plankton and other suspended organic matter. Their predators include birds, crabs, carnivorous mollusks, sea stars, and fish. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae. Their commensal, parasitic, or symbiotic relationships have not been formally documented. From a conservation perspective Pallid Dwarf Mactra Shells 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: Corbula altirostris, Mactra angulata, Mactra bistrigata, Mactra goniata, Mactra lacinata, Mactra pallida, Mulinia bradleyi, Mulinia camina, and Mulinia donaciformis.