Poulson’s Rock Shell, Roperia poulsoni

Poulson’s Rock Shell, Roperia poulsoni. Size: 5.8 cm (2.3 inches) x 3.0 cm (1.2 inches). Shell collected off the beach of Bahía Concepción, Baja California Sur, October 2019. Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Poulson’s Rock Shell, Roperia poulsoni (P.P. Carpenter, 1864), is a member of the Muricidae Family of Rock Shells. The genus Roperia is one of one hundred ninety-eight genera in this family, and this is the only species in this genus. They are also known as Poulson’s Dwarf Triton. The genus Roperia is named in honor of the mid to late 1800’s naturalist E.W. Roper, who first collected this species for scientific research.

Description: Poulson’s Rock Shells are spindle-shaped and consist of six whorls that become increasingly convex as they descend. They have a high spire. The shell is sculpted with nine varices, which cross spiral ridges, giving the entire exterior a knobby texture. The aperture is about half as long as the entire shell. The outer lip of the aperture is scalloped on the outside and there are three to four small “teeth” (dentitions) on the inside. The columella is smooth and wide. The siphon canal is open. The exterior of the shell is gray in color, with white and brown spiral lines. The interior is shiny white. These shells are often encrusted with bryozoans, like the above photographed specimen. Poulson’s Rock Shells reach a maximum of 6.5 cm (2.6 inches) in length and 3.4 cm (1.3 inches) in height.

Habitat and Distribution: Poulson’s Rock Shells are found on rocks in the intertidal zone to depths up to 4 m (15 feet). They are found a subtropical Eastern Pacific species. They have a limited range in Mexican waters. They are found along the west coasts of the Baja Peninsula, from the northern border to Magdalena Bay, Baja California Sur.

Ecology and Behavior: Poulson’s Rock Shells are a poorly studied and understood species. There is very limited documentation of their range, diet, predation, reproduction or ecosystem interactions. Other species in Family Muricidae are predators that feed primarily on other mollusks.  They are gonochoric and reproduce sexually, with internal fertilization. The eggs are laid in protective capsules. There is no mention in the available literature of them engaging in any types of commensal, parasitic, or symbiotic relationships. From a conservation perspective they have not been formally evaluated.

Synonyms: Fusinus (Roperia) roperi, Fusus (Roperia) roperi, Fusus roperi, Ocenebra poulsoni, and Ocinebra poulsoni.