The problem with a beach picnic is that sand ends up in the salsa and the potato salad, and no one likes eating sand. There's a creature, though, that eats it in order to survive: the sand dollar.
Most folks know the sand dollar from the souvenir shops and the beaches, where it's white, smooth, and flat -- a lot like a coaster. A specimen in the water, by contrast, is darker in color, sometimes even dark purple, and covered with short spines that lend it a velvety texture. Also, a sand dollar often stands on its side when it's feeding -- less like a coaster on a tabletop than a potato chip sticking out of the clam dip.
No matter how a sand dollar feeds -- on its side or flat on the bottom -- it ingests a fair amount of sand in the process. An older sand dollar will expel the sand, while a younger one will stash some of the sand in a portion of its intestine. The added weight stabilizes the youngster in turbulent waters and shifting sands.
Click here to learn more about the sand dollar.