Mexican Comb Lucine Shell, Ctena mexicana

Mexican Comb Lucine Shell, Ctena mexicana. Shell collected off the beach at Punta Chivato, Baja California Sur, May 2024. Size: 2.2 cm (0.9 inches) x 1.9 cm (0.7 inches) x 0.4 cm (0.2 inches). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Mexican Comb Lucine Shell, Ctena mexicana. Shell collected off the beach at Punta Chivato, Baja California Sur, May 2024. Size: 2.2 cm (0.9 inches) x 2.1 cm (0.8 inches) x 0.5 cm (0.2 inches). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato, Baja California Sur.

Phylogeny: The Mexican Comb Lucine Shell, Ctena mexicana (Dall 1901), is bivalve mollusk in the Lucinidae Family of Lucine Shells, and the Codakiinae Subfamily. The Ctena Genus is one of six genera in the Codakiinae Subfamily, and there are fifteen species in the Ctena Genus.

Description: Mexican Comb Lucine Shells are ovate in outline and moderately inflated in profile. The anterior end may be longer than the posterior, especially in smaller specimens. The beaks are fairly sharp and point toward the anterior end (prosogyrous). These shells are sculpted with numerous strong radial ribs and weaker commarginal striae. This crisscross pattern may produce a spinous region on the dorsal margins. The radial ribs are visible inside the shell, especially near the beaks and ventral margin. Mexican Comb Lucine Shells are white in color. They reach a maximum of 2.2 cm (0.9 inches) in length.

Habitat and Distribution: Mexican Comb Lucine Shells are found in sand in the intertidal zone, and to depths up to 100 m (330 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 Punta San Pablo, Baja California Sur, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior: Mexican Comb Lucine Shells are suspension feeders that feed primarily on plankton and other suspended organic matter. Mexican Comb Lucine Shells host symbiotic sulfur-oxidizing bacteria in specialized gill cells called bacteriocytes. They live in environments with sulfide-rich sediments. The shell pumps sulfide-rich water over its gills to provide the bacteria with sulfur and oxygen. These endosymbiotic bacteria then use these substrates to fix carbon into organic compounds, which are then transferred to the host as nutrients. If they lack sufficient food sources, Mexican Comb Lucine Shells can digest their symbionts as food. They are preyed upon by crabs, fish, and gastropods. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. 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: Codakia (Jagonia) mexicana and Lucina pectinata.