Solid Ark Shell, Arcopsis solida

Solid Ark, Arcopsis solida.  Size: 1.9 cm (0.7 inches) x 1.1 cm (0.4 inches). Shell collected from within a tidal pool at El Tule, Km 17, Baja California Sur, October 2018.

Phylogeny: The Solid Ark Shell, Arcopsis solida (G.B. Sowerby I, 1833), is a bivalve mollusk that is a member of the Noetiidae Family of Ark Shells. The genus Arcopsis is one of thirteen genera in this family, and there are four species in this genus. They are also known as the Garbanzo Clam Shell and in Mexico as Arca Diminuta.

Description: Solid Ark Shells are small, with a quadrate outline and an inflated profile. The anterior end is rounded. The posterior is slightly longer and somewhat truncate. The surface is sculpted with  40-50 fine radiating ribs. The shell is yellowish white in color. They have a thin periostracum. Solid Ark Shells reach a maximum of  1.9 cm (0.7 inches) in length and 1.1 cm (0.4 inches) in height.

Habitat and Distribution: Solid Arks are found mud, rocks, and stones in the intertidal zone, and to depths of 50 m (165 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.

Ecology and Behavior: Solid Arks 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, or symbiotic relationships has not been formally documented. From a conservation perspective they have not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.  

Synonyms: Barbatia digueti and Byssoarca solida.