Five-hole Sand Dollar, Mellita quinquiesperforata

Five-hole Sand Dollar, Mellita quinquiesperforata. Collected off Tigertail Beach, Marco Island, Florida, January 2019. Diameter: 7.2 cm (2.8 inches).

Phylogeny: The Five-hole Sand Dollar Mellita quinquiesperforata (Leske, 1778), is a member of the Mellitidae Family of Keyhole Sand Dollars. The genus Mellita is one of five genera in this family, and there are five species in this genus. They are also known as the Five-slotted Sand Dollar and the Keyhole Urchin and in Mexico as the dólar de arena and galleta de mar.

Morphology:  Five-hole 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.  Five-hole Sand Dollars have five slit-shaped lunulae, two toward the bottom, two just above the horizontal mid-line, and a larger one between the bottom slits. Living specimens may be green, brown, tan, or gray in color. Dead specimens quickly bleach white. Five-hole Sand Dollars reach 14 cm (5.5”) in diameter.

Habitat and Distribution:  Five-hole Sand Dollars live in sand. They are most common in bays, near inlets. They are found intertidally, and to a depth of 180 m (590’). They range from Virginia, throughout the Gulf of Mexico, to Brazil. In Mexican waters, they are found along the entire Gulf of Mexico coastline, but seem to be less common along the Yucatán Peninsula. This is the only sand dollar species found along Mexico’s East coast.

Diet:  Five-hole Sand Dollars are depositional feeders consuming algae, copepods,  larval crustaceans, diatoms, detritus and mollusks.

Predators:  Five-hole Sand Dollars are preyed upon by fish, including the Windowpane Flounder, Scopthalmus aquosos, and Haddock, Melanogrammus aeglefinis, and mollusks including the Scotch Bonnet, Phalium granulatum.

Reproduction: Five-hole Sand Dollars are gonochoric (male or female for life). They can reproduce asexually, through larval cloning, or sexually through external fertilization. The 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. Young sand dollars ingest sand and store it in their gut, to serve as ballast.

Ecosystem Interactions:  Five-hole Sand Dollars are know to host and have a commensal relationship with  the Pea Crab, Dissodactylus crinitichelis. The crabs hide under the oral surface and within the lunulae. The crabs gain a safe place to live and consume food displaced by the sand dollars movement through the sand. This species, like many sand dollars, plays a role in making soft sediments more habitable for other species. The sand dollar’s movement plows the surface of the substrate allowing for increased oxygen and nutrient penetration.

Human Interactions: Five-hole Sand Dollars have been the target of private and commercial curio collectors for centuries. They are also taken as bycatch in trawling  activities. These activities are known to reduce localized populations. Otherwise, this species has limited impact on human activities. From a conservation perspective they have not been evaluated. They are fairly common and have a wide distribution and should be considered to be of Least Concern.

Synonyms:  Clypeaster pentaporus, Echinodiscus quinquies perforatus, Echinodiscus quinquiesperforata, Echinus pentaporus, Mellita ampla, Mellita lata, Mellita latiambulacra, Mellita pentapora, Mellita quinquefora, Mellita quinquiesperforata lata, Mellita quinquiesperforata latiambulacra, Mellita testudinata, Mellita testudinata, Mellita testudinea, Scutella pentapora, and Scutella quinquefora.