Pismo Clam Shell, Tivela stultorum

Pismo Clam, Tivela stultorum. Shell collected from within the estuary of the Magdalena Bay complex, Baja California Sur, October 2018. Size: 10.2 cm (4.0 inches) x 8.1 cm (3.2 inches).

Pismo Clams, Tivela stultorum. Collections from the intertidal zone of Bahía Santa Rosalillita, Baja California, September 2015. Sizes: 13 cm (5.0 inches) to 15 cm (6.0 inches). Collection, photograph and identification courtesy of Barry Mastro, Escondido, California.

Phylogeny: The Pismo Clam Shell, Tivela stultorum (Mawe, 1823), is a bivalve mollusk that is a member of the Veneridae Family of Venus Clam Shells. The genus Tivela is one of one hundred seven genera in this family, and there are twenty-eight species in this genus. They are also known as the Giant Tivela Shell and in Mexico as Almeja Pismo and Trivela de Pismo.

Description: The Pismo Clam Shell has a thick, heavy, and inflated shell. They have a trigonal outline, with both ends being well rounded.  The beak is centered between the ends, the hinge is strong, and they have short siphons. The exterior surface of the shell is sculpted with fine commarginal striae. The exterior shell color is cream to gray or buff color, often with purple-brown radiating bands. Many are covered by varnish-like periostracum. The interior is white. Pismo Clam Shells reach a maximum of 17.6 cm (6.9 inches) in length and 14.0 cm (5.5 inches) in height.

Habitat and Distribution: Pismo Clam Shells are found buried in sand along beaches exposed to surf. They live intertidally and to depths of 30 m (98 feet). They are a subtropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean being limited from Magdalena Bay, Baja California Sur, north along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior: Pismo Clam Shells are suspension feeders, which feed on plankton and suspended organic matter. They are prey for fish, crabs, shore birds and gastropods. They are gonochoric and reproduce sexually, through broadcast spawning. Spawning begins in July, peaks in late summer, and ends in November. Pismo Clams are known to host parasitic cestodes, trematodes, and polychaetes. They sometimes host  pea crabs, from the genus Fabia, in a commensal relationship. They are edible and the target of commercial and recreational fisheries. From a conservation perspective they are considered to be of Least Concern.

Synonyms: Cytherea crassatelloides, Cytherea (Trigonella) crassatelloides Cytherea dubia, Cytherea intermedia, Cytherea solidissima, Cytherea virginea, Donax stultorum, Tivela (Pachydesma) stultorum, Tivela scarificata, and Trigonella crassatelloides.