Pacific Turkey Wing Shell, Arca pacifica

Pacific Turkey Wing Shell, Arca pacifica. Size: 4.0 cm (1.6 inches) x 1.9 cm (0.7 inches).  Shell collected off the beach at Km 26, Cero Colorado, Baja California Sur, March 2010.

Phylogeny: The Pacific Turkey Wing Shell, Arca pacifica (G.B. Sowerby I, 1833), is a bivalve mollusk that is a member of the Arcidae Family of Ark Shells.  The genus Arca is one of thirty-five genera in this family, and there are fourteen species in this genus. They are known in Mexico as  Concha Arca.

Description: Pacific Turkey Wing Shells are somewhat variable in shape, but are generally oblong or subquadrate, with a broad, flat surface on the hinge side. The beaks are separated by this surface. The anterodorsal margin comes to a point. The posterior end is indented and there is a broad radial furrow on the posterior slope. There is a gap along the valve margin. Young specimens are white with beautiful brown to violet brown zigzags. Older shells are grayer and have a rougher surface. The shell is usually covered by a thick, brown periostracum. The interior is white, with irregular brown staining.  Pacific Turkey Wing Shells reach a maximum of 15.6 cm (6.1 inches) in length and 7.4 cm (2.9 inches) in height.

Habitat and Distribution: Pacific Turkey Wing Shells are found attached rocks, in the intertidal zone, and to depths of 137 m (450 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean, including the Revillagigedo Islands, with the exception that they are absent north of Magdalena Bay, Baja California Sur along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior:  Pacific Turkey Wing Shells are suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Their engagement in any type of commensal, parasitic, commensal, or symbiotic relationship has not been formally documented. From a conservation perspective the Pacific Turkey Wing Shells is currently considered to be of Least Concern, with widely distributed stable populations.

Synonyms:  Byssoarca pacifica.