Sand Dollar - Lifestyle and Habitat

Lifestyle and Habitat

Sand dollars live beyond the mean low water line on top of or just beneath the surface of sandy or muddy areas. The spines on the somewhat flattened underside of the animal allow it to burrow or to slowly creep through the sediment. Fine, hair-like cilia cover the tiny spines. Podia that line the food grooves move food to the mouth opening, which is in the center of the star-shaped grooves on the underside of the animal (called the oral surface). Its food consists of crustacean larvae, small copepods, diatoms, algae and detritus.

On the ocean bottom, sand dollars are frequently found together. This is due in part to their preference for soft bottom areas, which are convenient for their reproduction. The sexes are separate and, as with most echinoids, gametes are released into the water column. They are conceived by external fertilization, as with most echinoids. The nektonic larvae metamorphose through several stages before the skeleton or test begins to form, at which point they become benthos.

In 2008, biologists learned sand dollar larvae clone themselves as a mechanism of self-defense. Larvae exposed to mucus from predatory fish respond to the threat by cloning themselves, thus doubling their numbers while effectively halving their size. The smaller larvae are better able to escape detection by fish, but may be more vulnerable to predation by smaller animals, such as crustaceans.

Sand dollars in their mature form have few natural predators, though ocean pouts and sunflower starfishes are known to eat them on occasion.