Trigonal Horse Hoof Shell, Pilosabia trigona

Trigonal Horse Hoof Shell, Pilosabia trigona. Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size:  1.7 cm (0.7 inches) x 1.4 cm (0.6 inches) x 0.7 cm (0.3 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Trigonal Horse Hoof Shell, Pilosabia trigona. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, May 2000. Size: 1.6 cm (0.6 inches) x 1.0 cm (0.4 inches).

Trigonal Horse Hoof Shell, Pilosabia trigona. Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size:  1.8 cm (0.7 inches) x 1.6 cm (0.6 inches) x 0.9 cm (0.4 inches). Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny: The Trigonal Horse Hoof Shell, Pilosabia trigona (Gmelin, 1791), is a gastropod mollusk that is a member of the Hipponicidae Family of Hoof Shells. The genus Pilosabia is one of eight genera in this family, and this is the only species in this genus. They are also known as the Bearded Horse Hoof Shell, the Triangular Bearded Hoof-Limpet Shell and the Trigonal Hoof Shell.  In Mexico they are known as Caracol Pezuña.

Description: The Trigonal Horse Hoof Shell has an ovate profile. The apex is moderately to highly elevated, and is often worn smooth. The exterior of the shell is sculpted with strong, fine ribs. The yellowish-brown periostracum forms bristles along these ribs that may extend over the edge of the shell, like a beard. The exterior of the shell is white to cream colored.  The interior is white with yellow, brown, or bluish blotches. Trigonal Horse Hoof Shells reach a maximum of 2.2 cm (0.9 inches) in length and 1.4 cm (0.5 inches) in height.

Habitat and Distribution: Trigonal Horse Hoofs are found on rocks within the intertidal zone, and at depths up to 6 m (20 feet). They are a subtropical to tropical Indian Ocean and Pacific Ocean species. In Mexican waters they range from Punta Chivato, Baja California Sur, to Guatemala. Some sources extend the range north to Puerto Penasco, Sonora. They are absent from the west coast of the Baja Peninsula.

Ecology and Behavior:  Trigonal Horse Hoof are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Other species in the Hipponicidae Family primarily feed on organic fragments, detritus, and pieces of algae. Because they are sedentary, they use their extendable snout to reach food sources and are dependent on water movement to bring them food. Some sources state that they are gonochoric, while other sources say they are sequential hermaphrodites, beginning life as males and transitioning into females. They reproduce sexually, through broadcast spawning. 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 wide distribution and should be consider to be of Least Concern.

Synonyms:  Amalthea barbata, Hipponix barbata, Hipponix (Pilosabia) trigona, Hipponix pilosus, Patella trigona, Pileopsis pilosus, and Pilosabia pilosa.