Two-banded Moon Shell, Polinices bifasciatus

Two-banded Moon Shell, Polinices bifasciatus. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2023. Size:  3.8 cm (1.5 inches) x 3.1 cm (1.2 inches). Collection, identification and photographs courtesy of Colin Campbell, DVM, Punta Chivato.

Two-banded Moon Shell, Polinices bifasciatus. Shell collected off the beach of Punta Chivato, Baja California Sur, May 2023. Size:  4.0 cm (1.6 inches) x 3.0 cm (1.2 inches). Collection, identification and photographs courtesy of Colin Campbell, DVM, Punta Chivato.

Two-banded Moon Shell, Polinices bifasciatus. Size: 5.1 cm (2.0 inches) x 3.9 cm (1.5 inches). Shell collected in the along the coast of Bahía Concepción, Baja California Sur, March 2015. Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Two-banded Moon Shell, Polinices bifasciatus (J. E. Gray, 1833), is gastropod mollusk that is a member of the Naticidae Family of Moon Shells. The genus Polinices is one of thirty-eight genera in this family, and there are forty-one species in this genus. They are also known as the Striped Moon Snail Shell Shell and in Mexico as Caracol Luna Rallado.

Description: Two-banded Moon Shells are globose and consist of about four whorls. They have a low spire and a fairly pointed apex.  The exterior of the shell is smooth and light-brown in color, with two, narrow, but widely separated, white bands. They have a large, smooth, semi-circular aperture. The area adjacent to the inner edge of the aperture is dark brown; the interior is white. The umbilicus is prominent. The Two-banded Moon Shells reach a maximum of 5.6 cm (2.2 inches) in length and 4.3 cm (1.7 inches) in height.

Habitat and Distribution: Two-banded Moons are found in mud and sand substrates in the intertidal zone, and to depths up to 60 m (197 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.

Ecology and Behavior: Two-banded Moon Shells are predators that feed primarily on clams such as the Mottled Bittersweet Clam Shell, Glycymeris maculata. They are gonochoric and reproduce sexually, with internal fertilization.  The eggs are laid in a “sand collar”. Their engagement in any type of commensal, parasitic, or symbiotic relationship has not been formulated. They have not been formally evaluated from a conservation perspective however, they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Natica bifasciata.