Ribbed Macron Shell, Macron aethiops

Ribbed Macron Shell, Macron aethiops. Shell collected off the beach of San Juanico, Baja California Sur, February 2023. Size: 4.0 cm (1.6 inches) x 2.6 cm (1.0 inch). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato.

Ribbed Macron Shell, Macron aethiops. Shell collected off the beach of San Juanico, Baja California Sur, February 2023. Size: 7.4 cm (2.9 inches) x 4.9 cm (1.9 inches). Collection, photograph and Identification courtesy of Colin Campbell, DVM, Punta Chivato.

Ribbed Macron Shell, Macron aethiops. Shell collected off the beach of Bahía Concepción, Baja California Sur, October 2019. Size: 8.1 cm (3.2 inches) x 5.0 cm (2.0 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

The Ribbed Macron, Macron aethiops (Reeve, 1847), is a gastropod mollusk that is a member of the Buccinidae Family of Whelks. They are also known as the Dusty Macron and the Ethiopian Macron. The Ribbed Macron is one of four species in the Macron genus. Early investigators believed the smooth version, Macron kellettii, was a separate species but E.A. Smith (1903) showed both forms constitute a single species.

The Ribbed Macron shells are stout that consist of five or six straight sided whorls, a moderate spire, a short, curved and wide siphonal canal, and a large oval aperture. Each whorl is broadly shouldered giving the shell a turreted look. Whorls are encircled with broad flat ribs, which vary in number and width, separated by broad grooves. Sometimes the ribs are absent all together. There is a small canal at the top of the white aperture and below a narrow, deep siphonal canal. Shells of live mollusks are covered with a thick greenish-brown to brown periostracum. Both the exterior and the interior of the shells  are white with a polished columella. Ribbed Macron Shells reach a maximum of 8.7 cm (3.4 inches) in length and 5.4 cm (2.0 inches) in height.

The Ribbed Macron are found attached to rocks, on and within muddy sand substrate between rocks in the intertidal zone to depths up to 3 m (10 feet). They are carnivores although they are reported to feed on dead fish and other carrion. They are found only in Western America and almost exclusively along the west coast south of Guerrero Negro, Baja California Sur and rarely within the Sea of Cortez. A smaller, smooth Macron, Macron orcutti ( Dall 1918), is found only in Magdalena Bay, Baja California.

Synonyms include Buccinum aethiops, Macron kellettii, Pseudoliva kellettii, and Purpura trochlea.