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 Guerrero Negro, 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.

Phylogeny: The Ribbed Macron Shell, Macron aethiops (Reeve, 1847), is a gastropod mollusk that is a member of the Buccinidae Family of Whelks. The genus Macron is one of eighteen genera in this family, and there are five species in this genus. They are also known as the Dusty Macron and the Ethiopian Macron. 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 World Registry of Marine Species (WoRMS) and MolluscaBase both place the genus Macron in the Family Buccinoidea incertae sedis. This means that they are uncertain where to place this genus and have temporarily placed it in this family type.

Description: Ribbed Macron Shells are stout, and consist of five or six straight-sided whorls. They have a moderate spire. The siphonal canal is deep and curved. There is a second canal, located at the top of the large oval aperture. Each whorl is broadly shouldered giving the shell a turreted look. The whorls are encircled with broad flat ribs, which vary in number and width, separated by broad grooves. Sometimes the ribs are absent all together. The siphonal canal is deep and curved. There is a second canal, located at the top of the aperture. The ribs extend onto the outer lip of the aperture. The inner lip is wide and shiny. They have a thick greenish-brown to brown periostracum. Both the exterior and the interior of these shells are white in color. 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 similar looking Smooth Macron Macron orcutti is smaller, smoother, and found only in Magdalena Bay, Baja California Sur.

Habitat and Distribution: Ribbed Macron Shells are found attached to rocks, and on  muddy sand substrates between rocks. They live in the intertidal zone, and at depths up to 3 m (10 feet). They are a subtropical to tropical Eastern Pacific species. In Mexican waters they are found along the west coast of the Baja Peninsula, from Punta Colonet, Baja California to Cabo San Lucas, Baja California Sur. There are reports of them being found in the southern most Gulf of California. There are also reports of them being found in Peru. It is unknown if this is based on misidentification or if this species is that discontinuous in its range.

Ecology and Behavior:  Ribbed Macron Shells are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. They are thought to scavengers that feed  on carrion. They are gonochoric and reproduce sexually, with internal fertilization.  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 however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Buccinum aethiops,  Pseudoliva kellettii, and Purpura trochlea.