Many-ribbed Ark Shell, Larkinia multicostata

Many-ribbed Ark Shell, Larkinia multicostatus. Shell collected off the beach at Punta Chivato, Baja California Sur, March 2022. Size: 6.4 cm (2.5 inches) x 7.3 cm (2.9 inches) x 3.1 cm (1.3 inches). Rib Count: 34. Photographs and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Many-ribbed Ark Shell, Larkinia multicostatus. Shell collected off the beach at Punta Chivato, Baja California Sur, December 2021. Size: 9.1 cm (3.6 inches) x 8.4 cm (3.3 inches) x 3.7 cm (1.5 inches). Rib Count: 34. Photographs and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

The Many-ribbed Ark, Larkinia multicostatus (G.B. Sowerby I, 1833), is a bivalve mollusk that is a member of the Arcidae Family of Arks. They are known in Mexico as arca piangua. The shell is a large heavy and inflated shell that is somewhat square in outline with a prominent beak. The outside is sculpted with 31 to 36 smooth radial ribs. The shell is white, but the outside is covered by a thick dark brown periostracum. The Many-ribbed Ark Shell reaches a maximum of 12.5 cm (4.8 inches) in length and 11.5 cm (4.5 inches) in height.

Many-ribbed Arks live in sand and mud habitats, intertidally to depths of 79 m (260 feet). They are found in all Mexican waters of the Pacific Ocean ranging from Southern California to Ecuador, including the Galapagos Islands and throughout the Sea of Cortez.

Synonyms include Anadara multicostata, Arca multicostata, Arca brandtii, and Arca comoluensis.