Three-winged Murex Shell, Pteropurpura trialata. Shell collected San Diego, California. May, 1998. Size: 6.7 cm (2.6 inches) x 3.4 cm (1.3 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Three-winged Murex, Albinistic Form, Pteropurpura trialata. Shell collected in San Diego, California, October 2019. Size: 6.5 cm (2.6 inches) x 3.2 cm (1.3 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Three-winged Murex Shell, Pteropurpura trialata (G.B. Sowerby II, 1834), is a gastropod mollusk that is a member of the Muricidae Family of Rock Shells. The genus Pteropurpura is one of one hundred ninety-eight genera in this family, and there are sixteen species in this genus. They are also known as the Western Three-winged Murex Shell and in Mexico as Murex de Tres Alas.

Description: The Three-winged Murex Shell has six whorls and a moderately high spire. They are sculpted with three thin varices which widen and get wavier as they approach the aperture. They have a closed, fairly long, siphon canal and an oval aperture. The exterior of the shell is white to tan, with numerous dark brown bands. Some specimens are all white. The interior is almost always white, but a small fraction are orange. Three-winged Murex Shells reach a maximum of 9.3 cm (3.7 inches) in length and 4.4 cm (1.7 inches) in height.

Habitat and Distribution: Three-Winged Murexes are found on rocks, either in protected waters or in deeper waters,  away from wave action, within the intertidal zone, and to depths up to 40 m (130 feet). They are a subtropical Eastern Pacific species that reside in Mexican waters of the Pacific Ocean that are found north of Magdalena Bay, Baja California Sur, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior: Three-winged Murex Shells are predators that feed primarily on gastropods, especially on the Worm Snail Serpulorbis squamigerus. They are gonochoric and reproduce sexually, with internal fertilization. The eggs are laid as a mass, on rocks or other hard substrates.  Their engagement in any type of commensal, parasitic or symbiotic relationship has not been formally documented. 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: Murex trialata, Pteropurpura (Pteropurpura) trialata, and Pterynotus trialatus.