Rugose Slit Keyhole Limpet Shell, Fissurella microtrema

Rugose Slit Keyhole Limpet Shell, Fissurella microtrema. Shell collected off the beach in the greater Los Cabos area, Baja California Sur, May 2019. Size: 1.8 cm (0.7 inches) x 1.4 cm (0.6 inches).

The Rugose Slit Keyhole Limpet, Fissurella microtrema (G.B. Sowerby, 1835), is a gastropod mollusk that is a member of the Fissurellidae Family of Keyhole Limpets. They are known in Mexico as lapas de cerradura. The shells have an irregular profile with a narrow anterior end, a small orifice, three strong ribs at the anterior that project onto the margin and the exterior surface is rough and irregularly ribbed. The exterior of the shell is variegated, with red or greenish rays, divided by lighter colored rays; the interior is white with a greenish or bluish tinge; the callus line is gray. Rugose Slit Keyhole Limpet Shells reach a maximum of 3.2 cm (1.3 inches) in length and 2.5 cm (1.0 inches) in height.

Rugose Slit Keyhole Limpets are found attached to rocks in the intertidal zone to depths up to 30 m (100 feet). They feed on algae that they scrape from the rocks with their radula. They range from the Cape Region to Ecuador and are found in the Central and Southern Sea of Cortez. They have not been documented from the West Coast of Baja.