Discordant Limpet Shell, Lottia discors

Discordant Limpet Shell, Lottia discors. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, January 2020. Size: 4.1 cm (1.6 inches) x 3.8 cm (1.5 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Discordant Limpet, Lottia discors (Philippi, 1849), is a gastropod mollusk that is a member of the Lottiidae Family of True Limpet Shells. The genus Lottia is one of fifteen genera in this family, and there are sixty-five species in this genus. They are also  known as the Confusing Limpet Shell and in Mexico as the Caracol Lapa.

Description: Discordant Limpet shells have an oval profile and vary from low to high-arched. The exterior of the shell is sculpted with numerous fine radial ribs. The apex is fairly central and often eroded. The exterior of the shell is grayish to white and in some specimens the darker rays show through under the eroded apex.  The interior is white with blue-gray, brown or greenish staining. Discordant Limpet Shells reach a maximum of 5.0 cm (2.0 inches) in length and 4.6 cm (1.8 inches) in height.

Habitat and Distribution: Discordant Limpets are found attached to rocks in the intertidal zone, and to depths up to 8 m (25 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, south of La Crucecita, Oaxaca along the coast of the mainland, and the central and northern portions of the Sea of Cortez. They are foiund around the Revillagigedo Islands and Tres Marias Islands.

Ecology and Behavior: Discordant Limpets are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Other species in Family Lottiidae are grazers that feed on algae. They are gonochoric and reproduce sexually, through broadcast spawning. 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:  Acmaea mutabilis, Collisella discors, Patella (Acmaea) discors, and Patella aenigmatica.