Ridged Cowry Shell, Cyphoma emarginatum
Ridged Cowry, Cyphoma emarginatum. Shell collected off the beach of Las Barilles, Baja California Sur, May 2017. Length: 3.0 cm (1.2 inches). Height: 1.7 cm (0.7 inches). Collection, photographs and identification courtesy of Bob Hillis, Ivins, Utah.
Ridged Cowry, Cyphoma emarginatum. Underwater photographs of actively feeding animals taken in Zihuantanejo Bay, Guerrero, January 2019. Photographs courtesy of Ron Woheau, Zihuantanejo. Note: the photographs above are of Ridged Cowries actively feeding in their native environment.
Phylogeny: The Ridged Cowry, Cyphoma emarginatum (G.B. Sowerby I, 1830) is a gastropod mollusk from the Ovulidae Family of Cowry Allies or False Cowrie Shells. The genus Cyphoma is one of forty-four genera in this family, and there are fourteen species in this genus. They are also known as the Emarginate Cyphoma, and in Mexico as Cyphoma Cresta.
Morphology: Ovulid shells differ from true cowries in that they have an inward curving spire, lack teeth on the inner lip of the aperture, and lack any color bands or spots. Ridged Cowries are elongate and narrowed at both ends. They have a very large retractable mantle that can cover the entire shell while they are feeding. The mantle is black with white proximal transverse striations that abruptly transition to yellow-orange at the margins. The mantle is randomly covered with back and white papillae. The siphon and tentacles are orangish. Their shell has a prominent transverse dorsal ridge. Some specimens are sculpted with fine striae. The aperture is long and crooked, with an open canal at both ends. The outer lip is thick and callused. The shell is beige to off-white in color. Ridged Cowries reach a maximum length of 3.0 cm (1.2 inches).
Habitat and Distribution: Ridged Cowries are found on gorgonians at depths between 3 m (10 feet) and 18 m (60 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.
Diet: Ridged Cowries are ectoparasitic carnivores that feed on gorgonians including the California Golden Gorgonian, Muricea californica.
Predation: As Ridged Cowries consume the gorgonian polyps, they incorporate the toxins, making themselves distasteful or poisonous to predators. Despite this defense mechanism they are still prey for hogfishes, pufferfishes, and crustaceans.
Reproduction: Ridged Cowries are gonochoric (male or female for life) and reproduce sexually, with internal fertilization. The eggs are laid, in mucous nets, on their gorgonian host.
Ecosystem Interactions: Other than the role that Rigid Cowries play in the food web, no interactions with other species have been documented.
Human Interactions: Rigid Cowries are occasionally the target of shell collectors. Otherwise, they have no significant impact on human activities. From a conservation perspective they have not been formally evaluated however they are common with a fairly wide distribution and should be consider to be of Least Concern.
Synonyms: Cyphoma emarginata, Cyphoma marginata, and Ovulum emarginatum.