Robust Carrier Shell, Xenophora robusta

Robust Carrier Shell, Xenophora robusta. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, November 2008. Size: 7.5 cm (3.0 inches) x 8.5 cm (3.3 inches). Identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Robust Carrier Shell, Xenophora robusta (A. E. Verrill, 1870), is a gastropod mollusk that is a member of the Xenophoridae Family of Carrier Shells. The genus Xenophora is one of six genera in this family, and there are fifteen species in this genus. In Mexico they are known as Caracol Portador. The Robust Carrier Shell is virtually identical to the American Carrier Shell, Xenophora conchyliophora, found in the Atlantic and the two are often confused in scientific records.

Description: The Robust Carrier Shell has a conical shape and is about half again as wide as tall. It has a large aperture and a blunt spire. The external surface of the shell is sculpted with wavy spiral ridges. The shell cements rocks, small shells, and other objects to its exterior. The exterior of the shell is white. The interior of the shell is white with brown staining.  Robust Carrier Shells reach a maximum of 10.8 cm (4.3 inches) in diameter.

Habitat and Distribution: Robust Carriers are found on rock, sand, and mud substrates. They are occasionally  found as shallow as  18 m (60 feet), but most are between 45m (150 feet) and 90 m (300 feet). Some are found as deep as 635 m (2082 feet). Most of these shells are collected by shrimp trawlers. 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:  Robust Carriers are grazers that feed primarily on microscopic algae, fine filamentous algae, and detritus. They are gonochoric and reproduce sexually,  with internal fertilization. Prior to the shell gluing on a new addition, it will clean the attachment site and attach sand grains to make a smooth attachment surface. Once a new addition is glued on, the shell will remain motionless for up to 10 hours to allow the bonding to set. They also host epibionts on their shells, such as bryozoans, corals, and sponges. This symbiotic relationship provides habitat for the hosted species and camouflage for the Robust Carrier. Their empty shells are used by hermit crabs for housing. From a conservation perspective the Robust Carrier has not been formally evaluated. However, they are fairly common with a relatively wide distribution and should be considered to be of Least Concern.

Synonyms: None