Eye-of-Judas Shell, Tribulus planospira

Eye-of-Judas Shell, Tribulus planospira. Size: 5.0 cm (2.0 inches) x 4.5 cm (1.8 inches). Shell collected off the beach in the greater Los Cabos area, Baja California Sur, August 2011.

Phylogeny: The Eye-of-Judas, Tribulus planospira (Lamarck, 1822), is a gastropod mollusk that is a member of the Muricidae Family of Rock Shells. The genus Tribulus is one of one hundred ninety-eight genera in the family, and this is the only species in this genus.

Description: Eye-of-Judas shells are bowl-shaped, and consist of three whorls. They have an almost flat spire, and a very large aperture. The exterior shell surface is sculpted with low and high ribs, that follow along the whorls and are most visible at the shoulder and at the outer lip of the aperture. The exterior of the shell is tan to brown in color.  The interior is white with reddish brown ribs running from the inside and outside lips. The inside lip also has a diagonal black rib. The Eye-of-Judas Shells reach a maximum of 8.3 cm (3.3 inches) in length and 7.5 cm (2.9 inches) in height.

Habitat and Distribution: Eye-of-Judas Shells are found on rocks, in the intertidal zone, and to depths up to 5 m (15 feet). They are a tropical Eastern Pacific species. In Mexican waters they range from the greater Cabo San Lucas area, Baja California Sur, to Guatemala, including the Revillagigedo Islands.

Ecology and Behavior: Eye-of-Judas Shells are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Other species in Family Muricidae are predators that feed primarily on bivalves, though some also eat crustaceans and sea urchins.  They are gonochoric and reproduce sexually. The eggs are laid in protective capsules. There is no mention in the available literature of them engaging in any types of parasitic, commensal, or symbiotic relationships. From a conservation perspective they have not been formally evaluated.

Synonyms: Haustrum pictum, Purpura lineatum, Purpura planospira, and Thais (Tribulus) planospira.