Panamic Bittersweet Clam Shell, Tucetona multicostata

Panamic Bittersweet Clam Shell, Tucetona multicostata . Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size: 4.2 cm (1.7 inches) x 4.0 cm (1.6 inches) x 1.3 cm (0.5 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny: The Panamic Bittersweet Clam Shell, Tucetona multicostata (G. B. Sowerby I, 1833) is a bivalve mollusk that is member of the Glycymerididae Family of Bittersweet Clam Shells. The genus Tucetona is one of four genera in this family, and there are forty-three species in this genus.

Description: Panamic Bittersweet Clam Shells are  ovate in outline and  moderately inflated. The exterior is sculpted by 31-43 radial ribs. The ribs may split either dorsally or ventrally. The hinge plate has 12-15 anterior teeth and 13-18 posterior teeth.  The exterior may be white or cream, with brown specks, chevrons, or bands. The interior is white or cream, with some specimens displaying brown spots or blotches. Panamic Bittersweet Clam Shells reach a maximum length of around 4.6 cm (1.8 inches).

Habitat and Distribution: Panamic Bittersweet Clam Shells are found on sand and mud substrates. They reside at depths between 8 m (26 feet) and 90 m (295 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean with the exception that they are absent from north of Magdalena Bay, Baja California Sur, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior:  Panamic 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: Glycymeris cardiiformis, Glycymeris multicostata, Pectunculus cardiiformis, Pectunculus multicostatus, Pectunculus parcipictus, and Pectunculus raripictus.