Small-holed Sand Dollar, Encope micropore
Small-holed Sand Dollar, Encope micropore. Sand Dollar collected from within the sand dunes of the barrier island Isla Santa Margarita off Puerto Adolfo Lopez Mateos, Baja California Sur, August 2016. Diameter: 9.2 cm (3.6 inches); depth: 1.2 cm (0.5 inches).
Small-holed Sand Dollar, Encope micropore. Underwater photograph taken in Zihuantanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.
The Small-holed Sand Dollar, Encope micropora (Agassiz, 1841), is a member of the Mellitidae Family of Keyhole Sand Dollars, and is known in Mexico as galleta de mar de hoyo pequeño. They have an extremely flattened rigid skeleton or test that consists of plates arranged in a five-fold radial symmetrical pattern with a rounded profile. The dorsal side of the test is slightly humped and the underside or oral surface is flat. 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. Their five circular lunulae which are almost always closed but may open to the margin on occasion. The test of living animals may be black, various shades of brown, or purple in color which quickly fades to a bleached white upon death. Small-holed Sand Dollars reach a maximum diameter of 13 cm (5.1 inches).
Small-holed Sand Dollars reside in sand substrate from the intertidal zone to depths up to 119 m (390 feet). They are normally found in colonies and in abundance when present. They consume algae, copepods, crustacean larvae, and detritus. In turn their larvae are preyed upon by small crustaceans and various fishes. Mature individuals are not subject to predation. 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.
In Mexican waters the Small-holed Sand Dollar is a resident of the Pacific but they are only present north of Magdalena Bay, Baja California Sur, along the central and northwest coasts of Baja during warm water El Niño event.
Synonyms include Echinoglycus cyclopora, Echinoglycus micropora, Encope cyclopora, and Encope occidentalis. Their relatives date to the Pliocene period, 7 million years ago.