Cortez Geoduck Shell, Panopea globosa

Cortez Geoduck Shell, Panopea globosa. Shell collected from within the estuary of the Magdalena Bay complex, Baja California Sur, October 2018. Size: 12.3 cm (4.8 inches) x 6.6 cm (2.6 inches).

Phylogeny: The Cortez Geoduck, Panopea globosa (Dall, 1898), is a bivalve mollusk that is a member of the Hiatellidae Family of Rock Borers and Giant Clam Shells. The genus Panopea is one of four genera in this family, and there are nine species in this genus. They are also known as the Globose Clam and the Mexican Geoduck and in Mexico as Almeja Chiluda. The common name Geoduck (pronounced gooey-duck) is from the Nisquali language, meaning “dig deep”.

Description: The Cortez Geoduck shell has an oval profile and is very inflated, especially around the centralized beak. The shell material may be  thin or thick. The shell  is sculpted with wavy growth ridges. They have a well rounded anterior end and the shell narrows toward the posterior end, where it ends abruptly. They have a gaping separation at the posterior end, through which the siphon passes; the gape is narrower at the anterior end. The exterior of the shell is white and semi-glossy; the interior is white. Cortez Geoduck shells reach a maximum length of 16.4 cm (6.5 inches) in length and 8.6 cm (3.4 inches) in height.

Habitat and Distribution: Cortez Geoducks are found buried in muddy sand substrate from the intertidal zone to depths up to 100 m (330 feet). They are a subtropical to tropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean from Magdalena Bay, Baja California Sur to Isla Pájaros, Sinaloa. They are found throughout the Gulf of California. The Cortez Geoduck is replaced along the central and northwest coasts of the Baja Peninsula by the similar looking but larger Pacific Geoduck, Panopea generosa.

Ecology and Behavior: Cortez Geoducks are suspension feeders that feed primarily on planktonic algae. They are prey for crabs, sea stars, fish, and gastropods. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Cortez Geoducks are known to host the pea crab Pinnaxodes gigas, in a symbiotic or  commensal relationship.  From a conservation perspective they have not been formally evaluated. Cortez Geoducks are the subject of artisanal, commercial, and recreational harvesting. As a result, many local populations have declined significantly, indicating that they should be a species of concern.

Synonyms: Panope taeniata, Panopea generosa taeniata, and Panopea generosa var. globosa.