Sea Cockroach Shell, Chiton articulatus

Sea Cockroach Shell, Chiton articulatus. Chiton collected from coastal waters off Santa Rosalillita, Baja California Sur, August 2019. Collection, photograph and identification courtesy of Barry Mastro, Escondido, California.

Phylogeny: The Sea Cockroach, Chiton articulatus (Sowerby, 1832), is a member of the Chitonidae Family of True Chiton Shells. The genus Chiton is one of fourteen genera in this family, and there are twenty-one species in this genus. They are also known as the Articulate Chiton Shell, the Dog’s Tongue Shell, and the Marine Cockroach Shell and in Mexico they are known as Cucaracha Del Mar.

Description: The Sea Cockroach is large in stature, with an oval outline and a low profile. The shell has a smooth dull surface and the central dorsal surface varies from tan to orangish in color. The radial areas are grayish tan to slate brown in color, usually with darker, fine, radiating lines. They have broad, black bands running the length of the shell. Adults are often eroded or overgrown with coralline algae. Sea Cockroaches reach a maximum of 10.0 cm (3.9 inches) in length.

Habitat and Distribution: Sea Cockroaches are found intertidally, attached to rocks, stones, and in crevices. They are a tropical Eastern Pacific species. They are ENDEMIC to Mexico ranging from Mazatlán, Sinaloa to Puerto Huatulco, Oaxaca, including the Revillagigedo Islands. The above photo, from Santa Rosalillita, Baja California Sur, indicates a range extension for this species to the west coast of the Baja Peninsula.

Ecology and Behavior:  Sea Cockroaches are thought to be herbivorous grazers, but they could be, like other species in the Chitonidae Family,  carnivores, detritivores, omnivores, or spongivores. In turn they are preyed upon by the Pacific Purple Snail, Plicopurpura columellaris. They are gonochoric and reproduce sexually, through broadcast spawning. They are known to host a great variety of epibionts including algae, annelids, arthropods, bryozoans, and mollusks. One  specimen hosted over 400 individual epibionts. Most of these relationships appear to be commensal in nature. Sea Cockroaches are probably the most abundant chiton in Mexican waters. From a conservation perspective the Sea Cockroach has not been formally evaluated. However, they are very common with a relatively wide distribution and should be considered to be of Least Concern. They are the only chiton found in Mexican waters of the Pacific Ocean that are harvested commercially for human consumption. Overharvesting has markedly reduced the number of individuals in some regions.

Synonyms: Chiton (Chiton) articulatus, Chiton laevigatus and Lophyrus striatosquamosus.