CLAM WORMS, SAND WORMS, AND TUBEWORMS: Polychaeta

PHYSICAL CHARACTERISTICS

Clam worms, sand worms, and tubeworms range in length from 0.078 inches to 9.8 feet (2 to 300 millimeters). Their bodies consist of a head, body trunk, and tail. Most species have long, segmented bodies that are tubelike and covered with bristles. Along the sides of their bodies are flaps that help them to swim, burrow, draw bits of food suspended in the water to their mouths, and grip surrounding rocks, sand, or mud. The side flaps are also used like gills to help them breathe underwater.

Clam worms, sand worms, and tubeworms vary in color, ranging from clear to light tan, red, pink, green, yellow, or a combination of these and other colors. The bodies of some species are shiny and reflect rainbowlike patterns. Their body shapes also vary and usually reflect their lifestyles. Active species, such as those that hunt for their food and some burrowers, have bodies with segments that are all very similar in appearance to one another. They have well-developed flaplike appendages, eyes, and other sensory organs. Some of these species have a mouth with tough jaws and the ability to extend part of their digestive tract outside the body to feed. Less active species, such as those living in tubes in sand or mud or in permanent burrows, have distinct body regions, each specialized to perform a certain job. Their fleshy side flaps are sometimes greatly reduced, even absent. Their mouths have tubes with special tentacles that help them to gather food.

GEOGRAPHIC RANGE

Clam worms, sand worms, and tubeworms are found in oceans and seas worldwide.

HABITAT

Clam worms, sand worms, and tubeworms are found in every ocean habitat from warm tropical seas to cold polar waters. They swim in open water or crawl along the seashore or sea bottom. Many species dig in muddy or sandy ocean bottoms to establish temporary or permanent burrows and tubes. Others are found among mussel beds on rocks or pilings, rocky reefs, or on corals. Some of these species live under rocks. Others live inside tubes made of sand or lime attached to rocks and corals. Some species are able to live in water that is less salty than the ocean. They live in estuaries (EHS-chew-AIR-eez), or areas where rivers meet the sea, and even in some freshwater habitats.

Some species live on the bodies of crustaceans (krus-TAY-shuns), or water-dwelling animals that have jointed legs and a hard shell but no backbone. The worms do not harm the crustaceans, but actually help them by keeping their breathing organs clean of organisms. Other species live inside the bodies of mussels, clams, oysters, and unsegmented worms as parasites (PAIR-uh-sites). Parasites live on or inside another animal and depend on them for food for their entire lives.

DIET

As a group, clam worms, sand worms, and tubeworms eat virtually all food resources in the ocean. Carnivores (KAR-nih-vorz) eat all kinds of small marine animals. Herbivores (URH-bih-vorz) feed on plant tissues. Omnivores (AM-nih-vroz) eat both plants and animals, dead or alive. These worms are raptorial, deposit, or suspension feeders. Raptorial (rap-TORE-ee-uhl) feeders are predators that actively hunt for their food. They extend part of their digestive tract out of the mouth and grab their prey with their hard jaws. Some species inject paralyzing venom into their prey.

Deposit feeders eat the surrounding sand or mud and digest whatever food in the form of detritus (dih-TRY-tuhs), bits of plants, animals, and animal waste, it contains. Selective deposit feeders use their sticky mouthparts or tentacles to capture and eat bits of food without having to swallow lots of mud and sand.

Suspension feeders either use their tentacles to stir up food into the water or sift food particles from water currents. Some burrowing species use their tentacles to pull water that carries floating food particles into their burrows.

BEHAVIOR AND REPRODUCTION

Some clam worms, sand worms, and tube-worms live in dense groups. Others live alone. Many species avoid light. They quickly take shelter under rocks or retreat inside their tubes or burrows when disturbed.

Most species of these worms require males and females to reproduce. Some will form temporary pairs during the breeding season. Males and females release their sperm and eggs into the water where fertilization takes place. Fertilization (FUR-tih-lih-ZAY-shun) is the joining of the egg and sperm to start development. After the eggs are fertilized, the pairs will become very aggressive and may eat each other. In other species, fertilization happens inside the body. The eggs are then released into the water, attached to some object, or kept inside the body until they hatch.

The larvae (LAR-vee), or animals in an early stage that change form before becoming adults, usually develop in open water. As they develop, additional segments are formed behind a special growth zone. Their lifespan can range from a few weeks to several years.

CLAM WORMS, SAND WORMS, TUBEWORMS, AND PEOPLE

Species of these worms respond quickly to increased amounts of pollution in the water and on the ocean bottom. Their presence or absence may indicate important changes in the marine environment. Some also harm oyster beds managed for harvesting.

YOU WANT A PIECE OF ME?

As clam worms, sand worms, and tube-worms grow, they can replace various body parts and even make new worms from broken bits of their own bodies. They can even replace the rear body segments if they are bitten or pulled off by a predator. Rear body segments are usually easy to replace, but a lost head is replaced only rarely. Some species use this ability as a means of reproducing without first having to find a mate. This is called asexual (ay-SEK-shuh-wuhl) reproduction.

CONSERVATION STATUS

Three species of clam worms, sand worms, and tubeworms are listed by the World Conservation Union (IUCN). Mesonerillaprospera is listed as Critically Endangered, or facing an extremely high risk of extinction in the wild. Erythrina polychaeta is Vulnerable, or facing a high risk of extinction in the wild. The Palolo worm, Eunice viridis, is also listed, but there is not enough information to determine if it is threatened.

FIRE WORM (Eurythoe complanata): SPECIES ACCOUNTS

Physical characteristics: The body of a fire worm is flat and long, measuring up to 4.7 to 5.5 inches (120 to 140 millimeters). The head has one pair of eyes, tentacles, and a pair of fleshy lobes associated with the mouth. The fleshy side flaps are well developed and have stiff, hollow bristles filled with defensive toxins. The bristles easily break off and cause a burning, stinging sensation when they come into contact with human skin. The fire worm also has blood red gill tufts, a part of the breathing system.

Geographic range: Fire worms live in all tropical seas.

Habitat: Fire worms live in crevices under and between rocks or in dead coral. They are also found in sand and mud.

Diet: Fire worms are omnivorous and will scavenge both dead plants and animals. They use their mouthparts to scrape and squeeze bits of food into their mouths. Prey is located by touch and also by special sensors that detect chemicals produced by other animals.

Behavior and reproduction: Males and females are not always required for reproduction. Some individuals may break up into one or more parts, with each part growing into a new individual.

Fire worms and people: Fire worms get their name because of their stings that cause burning and swelling.

Conservation status: Fire worms are not considered endangered or threatened. ∎

TUBEWORM (Serpula vermicularis): SPECIES ACCOUNTS

Physical characteristics: The body of a tubeworm is pale yellow to red and has up to 200 segments. It measures up to 1.9 to 2.7 inches (50 to 70 millimeters) long. The head is crowned with numerous tentacles that spread out into circular, feathery fans when extended outside the tube. The head also has a pinkish white, funnel-shaped cover. The cover acts as a cork when the worm withdraws inside its tube. The hard tube is made of calcium carbonate and has a few irregular ridges.

Geographic range: Tubeworms live in the northeast Atlantic Ocean and the Mediterranean Sea.

Habitat: Tubeworms live in depths to 820 feet (250 meters). They live in hard tubes attached to hard surfaces, such as rocks, stones, and bivalves. Bivalves are clams, mussels, oysters, and other aquatic animals with shells made up of two parts or halves.

Diet: They use their fanlike tentacles to create currents that draw in water carrying bits of floating food.

Behavior and reproduction: Tubeworms are usually solitary in open waters, but in sheltered habitats dense populations of tubes, they may form small reefs.

Every summer males and females release sperm and eggs into the water where fertilization takes place. The larvae reach adulthood in less than one year. Their entire life cycle takes anywhere from two to five years.

Tubeworms and people: The tubeworms' permanent tubes help to create habitats for other marine species.

Conservation status: Tubeworms are not considered endangered or threatened. ∎

HONEYCOMB WORM (Sabellaria alveolata): SPECIES ACCOUNTS

Physical characteristics: Honeycomb worm adults measure 1.1 to
1.5 inches (30 to 40 millimeters) long. The body trunk has three pairs of flattened bristles that form a cover to close the tube opening. The colors of the tubes are determined by the sand and other materials used to construct them.

Geographic range: Honeycomb worms are found in the Mediterranean Sea and north Atlantic to south Morocco. They are also found in the British Isles to its northern limit in the northeast Atlantic.

Habitat: Honeycomb worms are found along open coasts. They need hard surfaces to attach their tubes, but require sand and shell fragments to make their tubes.

Diet: They eat seston (SEHS-tun), bits of plant and animal materials that float by in the water during high tide.

Behavior and reproduction: The honeycomb worm lives in dense colonies and builds tubes that are permanently attached to hard surfaces. The tubes are made using coarse sand and/or bits of shells. The openings to the tubes are so tightly packed together they resemble a honeycomb. The tubes are up to 7.8 inches (20 centimeters) in length, with openings up to 0.19 inches (5 millimeters) in diameter. If the tubes are exposed during low tide, the worms will survive by plugging the entrance with a cover to avoid drying out or being eaten by other animals.

Males and females reproduce every year. The female produces from one hundred thousand to one million eggs at a time. The larvae eat plankton, or microscopic plants and animals drifting in water. Larvae may drift up to 6.2 miles (10 kilometers) from where they hatched.

Honeycomb worms and people: The reefs created by honeycomb worm tubes help to create habitats for other marine species. Fishermen collect and use honeycomb worms as bait.

Conservation status: The honeycomb worm is not considered endangered or threatened. ∎

FOR MORE INFORMATION

Books:

Blaxland, B. Earthworms, Leeches, and Sea Worms. New York: Chelsea House Publications, 2002.

Brusca, N. C., and G. J. Brusca. Invertebrates. 2nd edition. Sunderland, MA: Sinauer Associates, 2003.

Periodicals:

MacDonald, I. R., and C. Fisher. "Life without Light." National Geographic 190, no. 4 (October 1996): 86-97.

Web sites:

"Annelids." Encyclopedia Britannica. http://www.britannica.com/eb/print?tocId=9110238&fullArticle=true (accessed on December 21, 2004).

"Introduction to Polychaetes." http://www.ucmp.berkeley.edu/annelida/polyintro.html (accessed on December 20, 2004).

"Reefkeeper's Guide to Invertebrates. Part 11: Potentially Dangerous Polychaetes." Aquarium Net. http://www.reefs.org/library/aquarium_net/0198/0198_2.html (accessed on December 21, 2004).

Videos:

The Biology of Annelids. Beaufort, SC: BioMedia Associates, 2000.