Spiny Slipper Limpet Shell, Bostrycapuls aculeatus 

Spiny Slipper Limpet Shell, Bostrycapuls aculeatus. Shell collected off the beach in Los Cabos area, Baja California Sur, May 2020. Size: 2.0 cm (0.8 inches) x 1.4 cm (0.6 inches).

The Spiny Slipper Limpet, Bostrycapuls aculeatus (Gmelin, 1791), is a gastropod mollusk that is a member of the Calyptraeidae Family of Cup-and-Saucer and Slipper Limpets. They are also known as the Prickly Slipper Limpet and in Mexico as pique espinoso. The shell has an oval to circular profile that is moderately arched, the apex is curved to one side, the exterior of the shell is sculpted with rows of scales or spines that spiral from the apex, and the shelf covers about one half of the shells interior and may be notched at either end or in the center. The exterior color of the shell is a yellowish brown or gray brown, and some have darker brown bands. The interior may have brown spots or blotches and the shelf is white. The Spiny Slipper Limpet Shells reach a maximum of 3.8 cm (1.5 inches) in length and 2.7 cm (1.0 inches).

The Spiny Slipper Limpets are found found attached to rocks and shells in the intertidal zone to depths up to 79 m (260 feet). They are found throughout the Sea of Cortez and are found circumtropically in warm seas around the world.

Synonyms include Calyptraea echina, Calyptraea hystrix, Crepidula aculeata, Crepidula californica, and Patella aculeata.