Echiurans: Echiura

Echiurans are found mostly in the ocean, but a few species live in other kinds of salty waters, such as estuaries (EHS-chew-AIR-eez), where rivers meet the sea. Most species are found in intertidal and shallow waters, but some live at depths of 32,808 feet (10,000 meters). They usually dig burrows in sand, mud, or other debris on the bottom. Some live in rock tunnels bored by other animals, or inside shells, dead corals, or under rocks. Echiurans often host crabs, mollusks, and other kinds of worms in their burrows as commensals (kuh-MEHN-suhls), where they scavenge extra food. Commensals are animals that live on or with other organisms, without harm to either one.