Cortez Oyster Shell, Crassostrea corteziensis

Cortez Oyster Shell, Crassostrea corteziensis.  Shell collected from within the tidal pools of El Tule, Km17, Baja California Sur, January 2019. Size: 11.9 cm (4.6 inches) x 6.4 cm (2.5 inches).

Phylogeny: The Cortez Oyster, Crassostrea corteziensis (Hertlein, 1951), is a bivalve mollusk that is a member of the Ostreidae Family of True Oyster Shells. The Crassostrea Genus  is one of sixteen genera in the Ostreidae Family, and there are seven species in the Crassostrea Genus. They are known in Mexico as Ostra de Cortez, Ostion de Placer and Ostion Nativa.

Description: The Cortez Oyster shell is heavy and thick with an irregular and somewhat comma-shaped profile. The left valve is more concave than the right. The exterior surface of the shell is rough, and cream or beige in color, with brownish blotches. The interior is white or cream, with purple tinges. The Cortez Oyster reach a maximum of 25 cm (9.8 inches) in length and 13 cm (5.1 inches) in height.

Habitat and Distribution: Cortez Oysters are found on rocks in lagoons and in estuaries. They are often associated with mangrove roots. They live in the intertidal zone, and to depths up to 2 m (6 feet). They are a subtropical to tropical Eastern Pacific species that are  found in Mexican waters of the Pacific Ocean on a limited basis ranging from Bahía Kino, Sonora, in the Sea of Cortez, south to Guatemala along the coast of the mainland.

Ecology and Behavior: Cortez Oysters are suspension feeders that feed primarily on planktonic algae. Their predators include: flatworms, crabs from the genus Callinectes, the Bullseye Puffer, Sphoeroides annulatus, the Van Brunt’s Sea Urchin, Echinometra vanbrunti, and the Gulf Sun Star, Heliaster kubiniji. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. They are known to host the endoparasitic protozoans Perkinsus marinus and Marteilia refringens. They also host parasitic prokaryotes. From a conservation perspective the Cortez Oyster has not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms:  Crassostrea (Crassostrea) corteziensis and  Ostrea corteziensis.