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 sand dollars. The genus Encope  is one of five genera in this family, and there are eleven species in this 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. In Mexico they are called galleta de mar de agujero grande.

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 diameter of 12.5 cm (5.0 inches).

Habitat and Distribution:  Large-holed Sand Dollars are found on sand. They live from the lower intertidal zone to depths of around 46 m (150 feet). This species has a limited distribution. It is found throughout the Gulf of California and on the West coast of the Baja Peninsula from Magdalena Bay to the Cape region. Large-holed Sand Dollars are often found in large groups, mixed with Small-holed Sand Dollars Encope micropora.

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 legal protections.

Synonyms:  Echinoglycus grandis and Encope agassizi.