Large-holed Sand Dollar, Encope grandis
Large-holed Sand Dollar, Encope grandis. Sand Dollar collected from within Bahía Concepción, Baja California Sur, June 1980. Diameter Size: 10.2 cm (4.0 inches). Collection, identification and photographs courtesy of Bob Hillis, Ivins, Utah.
Phylogeny: The Large-holed Sand Dollar, Encope grandis L. Agassiz, 1841 is a member of the Mellitidae Family of Keyhole Sand Dollars. The Encope genus is one of five genera in the Mellitidae Family, and there are eleven species in the Encope genus. This species is also known as the Arrowhead Sand Dollar, the Giant Keyhole Sand Dollar, the Large-hole Sand Dollar, the Ornate Single Notched Sand Dollar and the Perforated Sand Dollar and in Mexico as Galleta de Mar de Agujero Grande. The genus name Encope comes from the Greek words meaning “cut into” and refers to the slots around the margin of the test.
Morphology: Large-holed Sand Dollars have a flattened profile and a somewhat circular outline, with five indentations equally spaced around the margin. Four of the five “arms” are rounded, while the fifth (posterior arm) is flattened or concave. The posterior hole (lunule) may be circular or oval. Living specimens vary in color from purple to black. Large-holed Sand Dollars reach a maximum of 12.5 cm (5.0 inches) in diameter.
Habitat and Distribution: Large-holed Sand Dollars are found on sand. They live from the lower intertidal zone to depths of 46 m (150 feet). They are often found in large groups, mixed with Small-holed Sand Dollar, Encope micropora. The Large-holed Sand Dollar is a subtropical to tropical Eastern Pacific species. They are endemic to Mexico, where they have a limited range. Large-holed Sand Dollars are found along the west coast of the Baja Peninsula from Magdalena Bay to Cabo San Lucas, Baja California Sur and throughout the Gulf of California.
Diet: Large-holed Sand Dollars are depositional feeders, feeding on detritus.
Predators: Very little is known about predation of Large-holed Sand Dollars. Their hard, bristly outer layer and their relative lack of edible parts discourages many potential predators. Similar species of sand dollars are eaten by crabs, fish including triggerfish, and sea stars. Younger sand dollars are most vulnerable to predation.
Reproduction: Large-holed Sand Dollars are gonochoric (male or female for life). They reproduce sexually through broadcast spawning. Fertilization is external. Millions of gametes are released into the sea, which come together for fertilization. The fertile eggs quickly hatch into planktonic larva. The larva pass through several stages of development before metamorphosing into their benthic adult form.
Ecosystem Interactions: Sand dollars play an important role in breaking up the surface layer of the sand. This allows more nutrients and oxygenated water to penetrate deeper into the sand, benefiting burrowing species. Large-holed Sand Dollars host commensal pea crabs, which live in the posterior anal lunule and feed either on the waste or the collected food of the sand dollar.
Human Interactions: Large-holed Sand Dollars are collected for personal collections and for sale as curios. This has impacted some local populations. This species has not been evaluated from a conservation perspective and does not, at present, have any form of legal protections.
Synonyms: Echinoglycus grandis and Encope agassizi.