Wide-mouth Purpura Shell, Plicopurpura columellaris
Wide-mouth Purpura Shell, Plicopurpura columellaris. Shell collected off the beach in the greater Los Cabos area, Baja California Suf, May 2018. Size: 5.9 cm (2.3 inches) x 4.1 cm (1.6 inches).
Phylogeny: The Wide-mouth Purpura Shell, Plicopurpura columellaris (Lamarck, 1822), is a gastropod mollusk that is a member of the Muricidae Family of Rock Shells. The genus Plicopurpura is one of one hundred ninety-eight genera in this family, and there are three species in this genus. They are also known as the Small-mouth Purpura Shell and in Mexico as Púrpura Patuda and as Púrpura Boca Pequeña. Sometimes shells in this genus are referred to broadly as Purple Shells because of the purple dye they produce.
Description: Wide-mouth Purpura Shells are so variable in shape and sculpture that they used to be separated into two different species- the Wide-mouth Purpura, Purpura pansa and the Small-mouth Purpura, Plicopurpura columellaris. Purpura Pansa had a much larger body whorl/aperture to spire ratio. Plicopurpura columellaris had a smaller ratio and dentition on both lips of the aperture. Now both are lumped together as Plicopurpura columellaris, though both common names are still used. These shells are large and solid and consist of three or four whorls. The body whorl and aperture can be very large or medium-sized. They have a prominent spire that varies, between individuals, in height and sharpness. The inner lip of the aperture is wide, and some have dentition inside the outer lip and folds on the columella. Their exterior is sculpted with spiral lines and nodules, which are more pronounced in smaller shells. The exterior of the shell is grayish green to dark gray. The interior is smooth and white, with some darker blotching. The inner lip of the aperture is brown to salmon in color and there is a dark brown band along the inside of the outer lip. Wide-mouth Purpura Shells reach a maximum of 10.0 cm (3.9 inches) in length and 6.9 cm (2.7 inches) in height.
Habitat and Distribution: Wide-mouth Purpuras are found attached to exposed rocks in the higher intertidal zone, and at depths up to 5 m (15 feet). They are a subtropical to tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean, including the Revillagigedo Islands, 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 and north of San Pedro Mártir Island, Baja California, in the Sea of Cortez.
Ecology and Behavior: Wide-mouth Purpuras are predatory carnivores that feed primarily on shelled mollusks. They are gonochoric and reproduce sexually, with internal fertilization. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formulated. From a conservation perspective they have not been formally evaluated. For centuries these shells have been harvested and milked for the purple dye that they produce. In the 1980’s commercial exploitation of these shells for Asian markets seriously threated their populations. In 1994 the Mexican government banned the commercial harvest of these shells. Poaching still impacts population levels in localized areas, but populations are recovering.
Synonyms: Buccinum rudolphi, Haustrum dentex, Plicopurpura pansa, Purpura pansa, and Purpura columellaris.