Pustulose Ark Shell, Anadara tuberculosa

Pustulose Ark Shell, Anadara tuberculosa. Size: 7.5 cm (3.0 inches) x 4.7 cm (1.9 inches). Shell collected off the beach at Km 26, Cero Colorado, Baja California Sur, March 2010. Identification courtesy of Bob Hillis, Ivins, Utah.

The Pustulose Ark, Anadara tuberculosa (G.B. Sowerby I, 1833), is a bivalve mollusk that is a member of the Arcidae Family of Arks. They are also known as the Black Arc and in Mexico as pata de mula and arca negra. The shells are solidly built, inflated, and equivalve. They have a rounded triangular outline, with a straight margin and rounded anterior and posterior ends. The outer surface is marked with approximately 35 radiating ribs, which lead to a slightly scalloped margin. Some of the ribs have tubercles. These shells are white, but are usually covered by a black periostracum. The Pustulose Ark Shell reach a maximum of 11 cm (4.3 inches) in length in width and 8.8 cm (3.5 inches) in height.

Pustulose Arks attach to mangroves with byssus and bury in soft mud. They live in the intertidal zone to depths of 20 m (65 feet). They range from Magdalena Bay, Baja California Sur, to Peru, including the southern third of the Sea of Cortez.

The Pustulose Ark Shell is similar in appearance to the Grand Ark Shell, Larkinia grandis (larger with 30 to 33 ribs).

Synonyms include Anadara senticostata and Arca tuberculosa.