Clipped Semele Shell, Semele decisa

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

Description: The Clipped Semele 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 Semeles 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. They are a subtropical Eastern Pacific species. In Mexican waters, they range from the northern border to Magdalena Bay, Baja California Sur. They are also found throughout the entire Gulf of California.

Ecology and Behavior: Clipped Semeles 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. 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: Amphibdesma decisa, Amphibdesma rubrolineatum, Semele (Semele) decisa, and Semele rubrotincta.