Large-holed Sand Dollar, Encope grandis

Large-holed Sand Dollar, Encope grandis. Diameter: 9.1 cm (3.6 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

The Large-holed Sand Dollar, Encope grandis (Agassiz, 1841), is a member of the Mellitidae Family of Keyhole Sand Dollars, and is known in Mexico as galleta de mar de agujero grande. They have an extremely flattened rigid skeleton or test that consists of plates arranged in a five-fold radial symmetrical pattern with an irregular rounded profile with five notched open lunulae. The margins between the notches are convex, except for the posterior margin, which is flat or concave and the posterior anal lunula may be rounded or elongated. The dorsal side of the test is slightly humped and the underside or oral surface is flat. The test is covered by a skin with spines that allow them to move across the seabed. They have a petal-like pattern that consists of five paired rows of pores. The mouth of the sand dollar is located on the bottom of its body at the center of the petal-like pattern. The test of living animals may be black or purple in color which quickly fades to a bleached white upon death. Large-holed Sand Dollars reach a maximum diameter of 12.5 cm (5.0 inches).

Large-holed Sand Dollars reside in sand substrate from the intertidal zone to depths up to 120 m (394 feet). They are normally found in colonies and in abundance when present. They consume algae, copepods, crustacean larvae, and detritus. They have separate sexes with reproduction by external fertilization. Eggs are brooded by the parents and the planktonic larvae metamorphose through several stages over a long period of time before the test forms, at which point they become benthic. Sand dollars also have the capability of larval cloning that is asexual reproduction, a mechanism of self-defense, that doubles their numbers while effectively halving their size which reduces predation Pea Crabs of the Genus Pinnotheres are known to live within the anal lunula of the Large-holed Sand Dollar.

In Mexican waters the Large-holed Sand Dollar is a resident of the Pacific but have a limited range being found from Magdalena Bay, Baja California Sur south to the greater Los Cabos area, Baja California Sur, and throughout the Sea of Cortez.

Synonyms include Echinoglycus grandis and Encope agassizi.