Mottled Bittersweet Clam Shell, Glycymeris maculata
Mottled Bittersweet Clam Shell, Glycymeris maculata. Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size: 7.3 cm (2.9 inches) x 7.2 cm (2.8 inches) x 0.3 cm (0.1 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.
Phylogeny: The Mottled Bittersweet Clam Shell, Glycymeris maculata (Broderip, 1832), is a bivalve mollusk that is member of the Glycymerididae Family of Bittersweet Shells. The genus Glycymeris is one of four genera in this family, and there are sixty species in this genus. They are also known as the Spotted Bittersweet Clam Shell and in Mexico as Almeja Indio and Almendra Manchada.
Description: The Mottled Bittersweet Clam Shell is heavy, inflated, and circular to ovate in outline. The exterior is sculpted with numerous flat radial ribs. The hinge plate is wide, with 12-15 teeth on each side of the beak. The interior ventral margin is sculpted with 40 – 65 crenulations (notches). The exterior is cream in color with irregular light brown blotches. Some may exhibit brown zigzags around the beak. The interior is cream, with some specimens having brown muscle scars and/ or brown blotches. The periostracum is thick, velvety, and brown to dark brown. Mottled Bittersweet Clam Shells reach a maximum length of 8.4 cm (3.25 inches). The similar looking Giant Bittersweet Shell, Glycymeris gigantea is larger and tends to have more widespread zigzags and chevrons.
Habitat and Distribution: Mottled Bittersweet Clam Shells are found buried in sandy substrates, often in lagoons and near mangroves. They live intertidally, and to a maximum depth of 84 m (276 feet). They are a subtropical to tropical Eastern Pacific species. In Mexican waters they are found throughout the Gulf of California and range south to Guatemala. Some sources extend this range to include the west coast of Baja California Sur as far north as Magdalena Bay.
Ecology and Behavior: Mottled Bittersweet Clam Shells are infaunal suspension feeders that feed primarily on planktonic algae and suspended organic matter. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. There is no mention in the available literature of them engaging in any types of parasitic, commensal, or symbiotic relationships. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.
Synonyms: Pectunculus maculatus.