Dark Spiny File Shell, Lima tetrica

Dark Spiny File Shell, Lima tetrica. Size: 4.2 cm (1.7 inches) x 3.1 cm (1.2 inches). Shell collected off the beach at Km 26, Cero Colorado, Baja California Sur, March 2010.

Dark Spiny File Shell, Lima tetrica. Size: 5.0 cm (2.0 inches) x 3.7 cm (1.5 inches). Shell collected off the beach in Loreto, Baja California Sur, March 2006. Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

The Dark Spiny File, Lima tetrica (Gould, 1851), is a bivalve mollusk that is a member of the File Shells of the Limidae Family. The species name “tetrica” comes from the Latin word meaning “gloomy” or “harsh.” The shell is sturdy with a somewhat triangular shape. Both valves are similar in size and shape (equivalve). They have only one pronounced auricle (ear) at the hinge and the shell is deeply ribbed with the ribs becoming increasingly scaly toward the margins. The shell is white in color. The Dark Spiny File Shell reach a maximum of 7.3 cm (2.9 inches) in length and 5.5 cm (2.2 inches) in height.

Dark Spiny File Shells are found on rock and sand bottoms from the intertidal zone to depths of 110 m (360 feet). They are suspension feeders. They range from Bahia Willard, Baja California in the northern end of the Sea of Cortez to Ecuador including the Cocos and Galapagos Islands. The Dark Spiny File Shell is very similar to the Pacific File Shell, Lima pacifica, but is smaller size and has less pronounced ribs.