Beard Worms: Pogonophora

Beard worms live in tubes made out of chitin (KYE-tehn) and protein. Chitin is a substance similar to fingernails that makes up the outer skeleton of some animals. The tubes are mostly below the surface of the ocean bottom, with just the upper end exposed. The yellowish, brownish, or black tubes are not branched. They are sometimes distinctly fringed, flared, segmented, or have a ringed pattern.

Most beard worm species are 3.94 to 29.53 inches (100 to 750 millimeters) in length, but are less than 0.039 inches (1 millimeter) thick. Their bodies have up to 200 tentacles on the head region. Each tentacle has tiny branches. The long, slender body trunk is followed by a small, segmented tail. The body is covered with a flexible, skinlike cuticle (KYU-tih-kuhl) that is covered with thick parts that create various patterns. Cuticle, unlike skin, is a body covering that is not made up of individual cells. Some beard worms have a collarlike ridge that rests on the rim of the tube when the worm's body is extended beyond the tube opening.

The nervous system includes a mass of nerves toward the head, a nerve cord running along the underside of the body, and a network of small nerve fibers. All of these are completely inside the skin. Under the skin is a thick layer of muscles that runs along the length of the body. The coelom (SIGH-lum), or main body cavity, is made up of a small cavity in the head region that connects to cavities inside each of the tentacles. A pair of cavities is found inside the body trunk. The segments of the tail also have a series of cavities inside, each separated by a layer of muscles.

Adults do not have a mouth or digestive system. Instead, they absorb bits of food from the water and mud directly through their tentacles and body trunk. They also have special tissues on their body trunk that contain bacteria that help to process food. The circulatory system is made up of parallel blood vessels along both their upper and undersides that run nearly the entire length of the body. The circulatory system is closed, with blood moving throughout the body inside the vessels.