Clipped Semele Clam Shell, Semele decisa

Clipped Semele Clam Shell, Semele decisa. Shell collected from within the estuary of the Magdalena Bay complex, Baja California Sur, October 2018. Size: 10.9 cm (4.3 inches) x 9.5 cm (3.8 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Clipped Semele Clam, Semele decisa (Conrad, 1837), is a bivalve mollusk that is a member of the Semelidae Family of Furrow Shells. The Semele Genus is one of fifteen genera in the Semelidae Family, and there are fifty-seven species in the Semele Genus. They are also known as the Bark Semele Shell and in Mexico as Almeja Blanca Mexicana. Semele was the mother of Dionysus in Greek mythology.

Description: The Clipped Semele Clam Shell is thick and fairly flat. They have a circular profile, except that they have a straight posterior end that appears to have been clipped off, hence their common name. The exterior has strong concentric ridge sculptures. The shells are covered with a light brown periostracum which often remains in the furrows between these ridges in worn shells. They have a white to tan exterior and a white with a purple tinge interior. A small portion of their population has concentric banding leading from the margin. The Clipped Semele Shell reaches a maximum of 12.0 cm (4.7 inches) in length and 10.5 cm (4.1 inches) in height.

Habitat and Distribution: Clipped Semele Clams reside buried in coarse sand, gravel or rubble. They are found in the intertidal zone, and to depths up to 46 m (150 feet). They are associated with rocky areas near exposed coastline. The Clipped Semele Clam is an subtropical Eastern Pacific species that have a limited range in Mexican waters of the Pacific Ocean being found north of Magdalena Bay, Baja California Sur, along the central and northwest coasts of the Baja Peninsula and throughout the Sea of Cortez.

Ecology and Behavior: Clipped Semele Clams are suspension feeders that feed primarily on plankton and suspended organic matter. In turn, they are prey for gastropods, sea stars, octopuses, and crabs. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. 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. From a conservation perspective the Clipped Semele Clams has not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: Amphibdesma decisa, Amphibdesma rubrolineatum, Semele (Semele) decisa, and Semele rubrotincta.