Unwashed Ark Shell, Fugleria illota

Unwashed Ark Shell, Fugleria illota. Size: 2.5 cm (1.0 inch) x 1.8 cm (0.7 inches). Shell collected off the beach at Km 26, Cero Colorado, Baja California Sur, March 2010. Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Unwashed Ark Shell, Fugleria illota (G.B. Sowerby I, 1833), is a bivalve mollusk that is a member of the Arcidae Family of Ark Shells. The genus Fugleria is one of thirty-five genera in this family, and there are three species in this genus. They are also known as the Dirty Ark. Ark shells obtain their name from their shell, which has alternating teeth along the hinge that allow the shell to close securely.

Description: The Unwashed Ark Shell has an oval to trigonal and inflated profile. They are inequilateral. The anterior and beak are rounded. The posterior is longer and truncate.  The exterior is sculpted with numerous, rounded radial ribs. The ribs are widely-spaced, and thicker at the posterior end. The ribs extend past the margin, giving the margin a serrated edge. The shell is dirty white to gray and covered with a brown hairy periostracum. Unwashed Ark Shells reach a maximum of 5.1 cm (2 inches) in length.

Habitat and Distribution: Unwashed Ark Shell are found attached to rocks and on mud within the intertidal zone, and to depths of 73 m (240 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of San Ignacio Lagoon, Baja California, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior:  Unwashed Ark Shells are suspension feeders, which feed on plankton and suspended organic matter. They are gonochoric and reproduce sexually, through broadcast spawning. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formally documented. From a conservation perspective the Unwashed Ark 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: Arca tabogensis, Byssoarca illota, and Barbatia illota