Sculptured Keyhole Limpet Shell, Diodora inaequalis

Sculptured Keyhole Limpet Shell, Diodora inaequalis. Shell collected off the beach in the greater Cabo San Lucas area, Baja California Sur, November 2020. Size: 2.4 cm (1.0 inch) x 1.6 cm (0.6 inches).

Phylogeny: The Sculptured Keyhole Limpet, Diodora inaequalis (G.B. Sowerby I, 1835), is gastropod mollusk that is a member of the Fissurellidae Family of Keyhole Limpets. The genus Diodora is one of forty-five genera in this family, and there are ninety-five species in this genus. They are also known as the Rocking Keyhole Limpet Shell and in Mexico as Lapa de Agujero Tallado.

Description: The Sculptured Keyhole Limpet Shell is elongate, with a base that is slightly narrower at the anterior end than at the posterior end. Its nearly parallel sides are arched, such that the shell will rock on its ends if placed on a flat surface. The apex is set somewhat forward. The orifice is elongated, and, in smaller individuals, notched on both sides. The exterior of the shell is sculpted with fine radiating ribs and even finer concentric lines. The exterior of the shell is gray with brown rays. The interior is white with a gray callus border. Sculptured Keyhole Limpet Shells reach a maximum of 2.7 cm (1.1 inches) in length and 1.6 cm (0.6 inches) in height.

Habitat and Distribution: Sculptured Keyhole Limpet are found on, and under, rocks in the intertidal zone, and to depths up to 37 m (120 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 the west coast of the Baja Peninsula.

Ecology and Behavior:  Sculptured Keyhole Limpets are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Most other species in the Fissurellidae Famioly are herbivorous grazers that feed primarily on algae, though some are detritivores or spongivores.  They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. There is no documentation of their involvement in parasitic, symbiotic, or commensal relationships. From a conservation perspective the Sculptured Keyhole Limpet has not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Fissurella (Cremides) pluridenta,  Fissurella inaequalis, Fissurella pluridenta, and  Rimula mazatlanica.