Sand dollars, disc-shaped marine creatures, often spark curiosity about their feeding mechanisms. Do these animals have teeth? Yes, but not in the conventional sense. Sand dollars are equipped with a complex chewing apparatus called Aristotle’s lantern. This structure processes their food and is important for their survival in sandy marine environments.
The Sand Dollar’s Mouth Structure
At the center of a sand dollar’s underside lies its mouth, housing a structure called Aristotle’s lantern. This apparatus consists of five jaw-like sections, each containing a pointed “tooth” made of calcified plates. These sections work in coordination to grind food particles. The structure can be extended outward to grasp food or retracted into the sand dollar’s body.
Feeding and Movement
Sand dollars use their Aristotle’s lantern to process the organic matter they consume. They are primarily deposit and filter feeders, relying on detritus, diatoms, algae, and microscopic organisms like plankton and crustacean larvae found in the sand and water. The lantern’s “teeth” grind these particles, sometimes for up to 15 minutes before ingestion. This grinding is necessary as their diet often includes abrasive sand particles.
Movement and feeding are closely linked. Their bodies are covered in tiny, velvety spines and tube feet, which gather food particles. These structures sweep food along their bodies towards the centrally located mouth. Sand dollars also use their spines and flattened body shape to burrow into the sand, for protection from predators or to position themselves for feeding. In calm waters, some species may stand upright, partially buried, to filter food from the water column, while in rougher conditions, they lie flat or fully burrow to stay anchored.
Beyond the Mouth: Other Fascinating Features
Beyond their specialized mouthparts, sand dollars exhibit other distinctive characteristics tailored to their marine habitat. Their flattened, disc-like shape, known as a test, is an adaptation for burrowing into sandy seafloors. This shape also helps them remain stable in strong currents, with some species having slits called lunules that prevent them from being swept away.
The familiar five-petal pattern on a sand dollar’s test represents specialized respiratory structures called petaloid ambulacra. These areas contain modified tube feet that facilitate gas exchange, allowing the sand dollar to extract oxygen from the surrounding water. Their body is also covered in a dense layer of small, flexible spines, often appearing in shades of gray, purple, or reddish-brown. These spines are used for movement across the seabed, burrowing, and keeping their bodies free of debris.