Saturn Keyhole Limpet Shell, Diodora saturnalis

Saturn Keyhole Limpet Shell, Diodora saturnalis. Shell collected off  the beach in the greater Los Cabos area, Baja California Sur, June 2019. Size: 2.5 cm (1.0 inch) x 1.5 cm (0.6 inches). Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Saturn Keyhole Limpet Shell, Diodora saturnalis (Carpenter, 1864), is a 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 known in Mexico as Lapa Saturna. They derive their name from their three-lobed keyhole that looks like a side view of the planet Saturn.

Description: Saturn Keyhole Limpet Shells have a broad oval profile and are thicker and have a higher profile than most other keyhole limpets in the area. The exterior of the shell is sculpted by radial ribs that may extend to the margins as crenulations. The keyhole is relatively small and set toward the anterior margin. The keyhole is oval, with a wider circle in the middle. The exterior of the shell varies from gray, green, pink, reddish, tan or whitish, with darker radiating bands. The interior is white with gray around the keyhole. Saturn Keyhole Limpet Shells reach a maximum of 2.5 cm (1.0 inch) in length and 1.5 cm (0.6 inches) in height.

Habitat and Distribution: Saturn Keyhole Limpets are found attached to rocks within lagoons and around mangroves. They live in the intertidal zone, and to depths up to 35 m (115 feet). They are a subtropical to tropical Eastern Pacific species. In Mexican waters they range from San Ignacio Lagoon, Baja California Sur, to Guatemala. They are found throughout the Gulf of California.

Ecology and Behavior:  Saturn Keyhole Limpet Shells are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Most other species in family Fissurellidae are herbivorous grazers that feed primarily on algae, though some are spongivores or detritivores.  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.

Synonym:  Glyphis saturnalis.