Hemichordates: Hemichordata

Acorn worms live alone sheltered in their burrows, under rocks, or in thick tangles of plants. The burrowing species use their snout for digging. They line the U-shaped burrows with mucus to strengthen the walls. One end of the "U" is a cone-shaped dent, and the other is a pile of feces (FEE-seez) a short distance away. The rest of the burrow is underground and sometimes has a few side tunnels. Burrowing acorn worms sometimes stretch their snout and collar out of the tunnel, but they spend most of their time underground.

Some hemichordates gather their meals by stirring up currents with the hairlike fibers on their body and drawing in nutrients from the water. Others take in particles of sand or mud and eat the nutrients sticking to them. Scientists are not sure whether hemichordates use mucus to capture prey. Some scientists believe food sticks to the mucus-covered snout and that hairlike fibers on the animal's body beat in a pattern that draws the mucus and the food together to the mouth. Other scientists have found that the animals use their hairlike fibers to change the direction of their movements and direct food particles to the mouth.

Hemichordates have separate sexes. They release their eggs and sperm into the water, where fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development, takes place. In some species the fertilized (FUR-teh-lyzed) eggs develop directly into adults. In most species, however, the fertilized eggs develop into free-floating larvae, which eventually settle on the bottom and transform into adults. Burrow dwellers develop tails that they use to anchor themselves in their mucus-lined tunnels. In some species of hemichordates reproduction is asexual and accomplished by the breaking up of the adult's body or by budding. Asexual (ay-SEK-shuh-wuhl) means without the uniting of egg and sperm for the transfer of DNA from two parents. In budding a bump develops on an animal, grows to full size, and then breaks off to live as a new individual.