These are tubes made by Parchment Worms, a type of tube worm that lives in shallow water. The worm buries itself in the sand, in a "U" shape, with both ends at the surface. It secrets chemicals that form these very tough, leathery tubes. The color and texture of these tubes give them their name, as it looks much like parchment.

The worm lives inside the tube, and has very specially adapted segments of its body that move back and forth in the tube to pump water in one end and out the other. The worm filters this water to get plankton, organic debris, and other food.

Other creatures often share the tubes with the worm. I have found crabs, other kinds of worms, snails, and even tiny brittle stars living inside the tubes.