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 Wonteau, Zihuantanejo.
Phylogeny: The Small-holed Sand Dollar, Encope micropora (L. Agassiz, 1841), is a member of the Mellitidae family of Keyhole Sand Dollars. The genus Encope is one of five genera in this family, and there are eleven species in this genus. They are known in Mexico as Galleta de Mar de Hoyo Pequeno.
Morphology: Small-holed Sand Dollars are in the Order Clypeasteriodea. Clypeaster means “round shield star”, referring to the outline shape and the 5-petalled pattern on the dorsal surface. Clypeasteroids are much flattened burrowing urchins. The dorsal side of the test is slightly humped and the ventral or oral surface is flat. They have a mouth (located centrally on the ventral surface) and a modified Aristotle’s Lantern (complex jaw structure). Grooves, lined with cilia, direct food to the mouth. The epidermis is covered with small spines, which facilitate movement over, and through, soft substrates. The petalloid design on top is made of pairs of pores. These pores allow for respiration through specialized tube feet. Small-holed Sand Dollars are round in outline. They have five oval lunulae (holes) located near the margin. These lunulae are almost always closed, but may break the margin on occasion. They have a sixth lunulae located closer to the center. When alive they are various shades of brown, purple or black and upon death become a uniform white, being bleached out by the sun. The Small-holed Sand Dollar reach a maximum of 13.0 cm (5.1 inches) in diameter and 1.2 cm (0.5 inches) in depth.
Habitat and Distribution: The Small-holed Sand Dollar resides on sandy bottoms, intertidally, and to depths of 119 m (390 feet). They are a tropical Eastern Pacific species and in Mexican waters of the Pacific Ocean range from Magdalena Bay, Baja California Sur, southward along the southwest coast of Baja, throughout the Sea of Cortez and southward along the coast of the mainland to Guatemala. If present they are normally found in colonies and in abundance. Following El Niño events, this species can be found in the coastal waters of Southern California.
Diet: Small-holed Sand Dollars are opportunistic omnivores. They consume algae, copepods, crustacean larvae, and detritus.
Predators: Larval Small-holed Sand Dollars are subject to predation by fish and small crustaceans. Mature sand dollars are generally thought to be free from predation, because their hard, bristly outer layer and their relative lack of edible parts discourages most potential predators. They are also preyed upon by crabs, including the Arched Swimming Crab, Callinectes arcuatus, the Giant Swimcrab, Callinectes toxotes, Moon Snails, the Nassarid Sea Snail, Northia pristis and Pagurid Hermit Crabs.
Reproduction: Small-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: Small-holed 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. There is very little documentation of the commensalism, parasitism, or symbiosis for this species.
Human Interactions: Small-holed Sand Dollars are collected for personal collections and for sale as curios. This does have an impacted some local populations. From a conservation perspective the Small-holed Sand Dollar has not been formally evaluated. At present they have no legal protection.
Synonyms: Echinoglycus cyclopora, Echinoglycus micropora, Echinoglycus perspectiva, Encope (Echinadesma) micropora, Encope (Echinadesma) perspectiva, Encope (Echinadesma) wetmorei, Encope cocosi, Encope cyclopora, Encope ecuadorensis, Encope fragilis, Encope irregularis, Encope laevis, Encope micropora cocosi, Encope micropora ecuadorensis, Encope micropora ecuadoriensis, Encope micropora fragilis, Encope micropora galapagensis, Encope micropora irregularis, Encope micropora tetrapora, Encope occidentalis, Encope perspectiva, Encope perspectiva jonesi, Encope perspetiva, Encope tetrapora, and Encope wetmorei.