Banded Top Shell, Agathistoma ligulata

Banded Top Shell, Agathistoma ligulata. 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, Agathistoma ligulata (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. This species has been divided into subspecies, based on geography. The subspecies Agathistoma ligulatum ligulatum and Agathistoma ligulatum mariamadrae 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 Top Shells reside on hard substrates in the intertidal zone, and to depths up to 100 m (330 feet). They are a tropical Eastern Pacific species. In Mexican waters they are found in the Sea of Cortez from Santa Rosalia to Cabo San Lucas, Baja California Sur, and south along the mainland coast to Guatemala. They have not been documented from the West Coast of the Baja Peninsula.

Ecology and Behavior:  Banded 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 Tegulidae are grazers, feeding on algae and detritus, or infaunal suspension feeders.  Sea stars, crabs, octopuses, and shore birds are common predators for these shells. They are gonochoric and reproduce sexually, through broadcast spawning, 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 however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms:  Tegula ligulata and Trochus ligulatus.