Palmer’s Top Shell, Callistoma palmeri

Palmer’s Top Shell, Callistoma palmeri. Shell collected off the beach of Punta Chivato, Baja California Sur, March 2025. Size: 2.4 cm (0.9 inches) in diameter, 2.4 cm  (0.9 inches) in height. Collection, photographs and identification courtesy of Colin Campbell, DVM, Punta Chivato.

Phylogeny:  Palmer’s Top Shell, Calliostoma palmeri (Dall, 1871, is a gastropod mollusk that is a member of the Calliostomatidae Family of Noble Top Shells. The genus Calliostoma is one of thirty-two genera in this family, and there are three hundred seventy-five species in this genus. They are known in Mexico as Calliostoma Palmer. The name of this family is derived from the Greek words kallos (beautiful) and stoma (mouth), referring to the pearly aperture found in most species.

Description: Palmer’s Top Shells consist of around 6 or 7 whorls and are about the same in height as they are in diameter. The whorls are marked with strong shoulders, giving the shell a somewhat turreted look. The spire is moderately high and pointy. The shell is sculpted with finely beaded lines that spiral down the sides and a spiral of stronger, smooth lines  on the base. The aperture is subquadrate, pearly, and smooth on both lips. The umbilicus is closed. Palmer’s Top Shells are smoothly polished and ivory in color, with fine revolving lines of chestnut brown. The umbilical region is blue or purple ( The above photographed specimen is unusually pale, possibly from fading or leucism). The maximum diameter for this species is 3.0 cm (1.2 inches). Palmer’s Top Shells are larger and squattier than the similar looking  Kelp Top Shell, Calliostoma bonita. Calliostoma eximium is also similar in appearance but has a pinkish or gray color, checkered with black, white, and red.

Habitat and Distribution:  Palmer’s Top Shells are found on rocks, in the intertidal zone and to a maximum depth of 45 m (148 feet). They are a subtropical Eastern Pacific species that have a very limited range in Mexican waters of the Pacific Ocean. They are endemic to the northern Sea of Cortez ranging as far south as Mulegé, Baja California Sur.

Ecology and Behavior:  Palmer’s Top Shells are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Other species in Family Calliostomatidae are very diverse in their diets. They may be detritovores, algae eaters, scavengers, or predators that eat sessile invertebrates. They are gonochoric and reproduce sexually,  with external 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.

Synonyms: None