PRIAPULANS: Priapulida

PHYSICAL CHARACTERISTICS

The body of priapulans (PRYE-uh-PUH-luhns) is divided into three parts: introvert (IN-troh-vert), trunk, and tail. The animals use a pair of muscles to pull the introvert completely into the trunk. Spines of various sizes and shapes cover the entire surface of the introvert. Inside the introvert is a muscular feeding tube armed with teeth.

The trunk houses the internal body organs, in particular the digestive system and reproductive organs. The body is filled with fluid that serves as a skeleton to support the body when the muscles of the body wall contract. When priapulans move, the fluid moves around in the body cavity and serves the functions of circulation, waste removal, and respiration. The tail is continuous with the body cavity of the trunk and may be used for respiration.

GEOGRAPHIC RANGE

Priapulans live all over the world.

HABITAT

Priapulans live in sand and mud in all oceans at all depths. Larger priapulans live in colder waters. Small priapulans are most common in shallow tropical waters.

DIET

Priapulans eat sea worms.

BEHAVIOR AND REPRODUCTION

With the introvert fully extended, priapulans grasp prey with their teeth and rapidly roll it inward. Priapulans depend on their fluid skeleton for movement. They use their extended introvert and the muscles of the front part of their trunk to anchor themselves in the sand. Once anchored, priapulans can pull themselves through the sand by contracting their body wall muscles.

Priapulans have separate sexes. They release their eggs and sperm into the water, where fertilization (FUR-teh-lih-zay-shun), or the uniting of egg and sperm to start development, takes place and larvae develop. Larvae (LAR-vee) are animals in an early stage that change form before becoming adults.

PRIAPULANS AND PEOPLE

Because they are considered living fossils, priapulans are important for research.

Did You Know?

The skeleton of priapulans is nothing but fluid.

CONSERVATION STATUS

Priapulans are not considered threatened or endangered.

NO COMMON NAME (Priapulus caudatus): SPECIES ACCOUNT

Physical characteristics: Priapulus caudatus is large, as long as 8 inches (200 millimeters). The body is strongly tubular and ringed. The introvert can be quite long when extended, as much as one-third the length of the trunk.

Geographic range: Priapulus caudatus (abbreviated as P. caudatus) lives in the Northern Hemisphere, from the Arctic Ocean to the Mediterranean Sea in the eastern Atlantic Ocean and to California in the eastern Pacific Ocean.

Habitat: P. caudatus lives in the sea on soft, muddy bottoms.

Diet: P. caudatus eats waste when young and is a predator of worms as an adult.

Behavior and reproduction: P. caudatus uses its fluid skeleton for movement. The introvert and forward part of the trunk act as an anchor in the mud. Once anchored, the animal pulls itself through the mud by contracting body wall muscles. P. caudatus has separate sexes. Eggs and sperm are released into the water, where they unite. The larvae live in the bottom mud. As the larvae grow, they shed their outer covering and gradually grow into young animals.

Priapulus caudatus and people: P. caudatus has no known importance to people.

Conservation status: P. caudatus is not considered threatened or endangered. ∎

FOR MORE INFORMATION

Books:

Nielsen, Claus. Animal Evolution. New York: Oxford University Press, 2001.

Valentine, James W. On the Origin of Phyla. Chicago: University of Chicago Press, 2004.

Young, Craig M., ed. Atlas of Marine Invertebrate Larvae. San Diego, CA: Academic, 2002.

Web sites:

"The Priapulida." Lamont-Doherty Earth Observatory. http://www.ldeo.columbia.edu/edu/dees/ees/life/slides/phyla/priapulida.html (accessed on February 3, 2005).

"Priapulid Evolution." Seattle University. http://classes.seattleu.edu/biology/biol235/hodin/nematodePriapulidGroup/priapulid/evolution.htm (accessed on February 3, 2005).