Banded Top Shell, Agathistoma liguiatum

Banded Top Shell, Agathistoma liguiatum. Shell provided courtesy of the commercial fishermen of the greater Los Cabos area, Baja California Sur, July 2013. Size: 1.6 cm (0.6 inches) x 1.2 cm (0.5 inches).

Phylogeny:  The Banded Top Shell, Agathistom liguiatum (Menke, 1850), is a gastropod mollusk that is a member of the Tegulidae Family of Top Shells. The genus Agathistoma is one of eight genera in this family, and there are twenty-five species in this genus. There are two subspecies that are found in different locations – the subspecies Agathistoma ligulatum ligulatum and Agathistoma ligulatum mariamadrae, that are found in different locations; they differ in the strength of spiral striations and color patterns.

Description: Banded Top Shell Shells are fairly low in profile, with straight-sided whorls that are often knobbed. The exterior of their shells is brown with white markings. The umbilical area is white. The Banded Top Shell is relatively small reaching a maximum of 1.6 cm (0.6 inches) in height and 1.2 cm (0.5 inches) in width.

Habitat and Distribution: Banded Tops reside on hard substrates in the intertidal zone, and to depths up to 100 m (330 feet). They are a 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 and north of Santa Rosalia, Baja California Sur, in the Sea of Cortez.

Ecology and Behavior:  Banded Tops are a poorly studied and understood species. There is very limited documentation of their diet, predation, reproduction or ecosystem interactions. Other species in the Tegulidae Family are grazers, feeding on algae and detritus, or infaunal suspension feeders.  Sea stars, crabs, octopuses, and shorebirds are common predators for these shells. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. They’re engagement in any type of commensal, parasitic, or symbiotic relationships has not been formally documented. From a conservation perspective the Banded Top 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:  Tegula ligulata and Trochus ligulatus.