Pacific Spiny Oyster Shell, Spondylus crassisquama

Pacific Spiny Oyster Shell, Spondylus crassisquama. Shell provided by the commercial fishermen of the greater Los Cabos area, March 2014. Size: 8.3 cm (3.3 inches) x 8.3 cm (3.3 inches). Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Pacific Spiny Oyster, Spondylus crassisquama (Lamarck, 1819), is a bivalve mollusk that is a member of the Spondylidae Family of Spiny Oyster Shells. Spondylus is the only genus in this family, and there are seventy-five species in this genus. This species is also known as the Pacific Thorny Oyster. They are known in Mexico as Ostra Espinosa. Pacific Spiny Oysters. They are a close relative of the American Spiny Oysters, Spondylus americanus, found in the Gulf of Mexico in the Atlantic Ocean.

Description: The Pacific Spiny Oyster shell is heavy and usually decorated with long curving spines. There are usually 6 radial rows of long spines, separated by rows of smaller spines. The spines are mounted on radial ribs. The left valve is more convex than the right valve, which is cemented to the substrate. The exterior of these shells vary in color from white to orange to red to purple in color. The interior is white with a border around the margin that matches the exterior color. Pacific Spiny Oysters reach a maximum of 15.6 cm (6.19 inches) in length and 15.6 cm (7.9 inches) in height. The similar looking Spiny Oyster Shell, Spondylus leucacanthus, has longer, more delicate, spines, which are often white. Also, the interior color band is generally only near the hinge. The similar looking Donkey Thorn Oyster Shell, Spondylus limbatus, has more irregular spathate (spatula-like) spines.

Habitat and Distribution: Pacific Spiny Oysters are generally found attached to hard vertical surfaces, though in some locations they live unattached, on pebbles, sand, or mud. They live at depths between 10 m (35 feet) and 91 m (300 feet). They are a subtropical to tropical Eastern Pacific species that are found in Mexican waters of the Pacific Ocean from Cedros Island, Baja California south to Guatemala. They are found in the Sea of Cortez, south from Bahía Willard, Baja California.

Ecology and Behavior:  Pacific Spiny Oysters are suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Pacific Spiny Oysters host many other species as epibionts, including algae, sponges, bivalves, marine worms, and crustaceans. Most of these relationships appear to be either commensal or symbiotic, with the epibionts getting a safe place to live, while camouflaging the host. From a conservation perspective they have not been formally evaluated.

Synonyms: Spondylus basilicus, Spondylus dubius, Spondylus pictorum and Spondylus princeps.