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Gastrotrichs: Gastrotricha

GASTROTRICHS: Gastrotricha

NO COMMON NAME (Lepidodermella squamata): SPECIES ACCOUNT


Gastrotrichs (GAS-truh-tricks) are microscopic water-dwelling worms shaped like straps, bowling pins, or various forms in between. They are 0.002 to 0.1 inch (50 micrometers to 3.5 millimeters) long. The body is flat on the bottom and arched on the top. The body covering is almost see-through, like fogged-up glass. The belly is covered with hairlike fibers. The body is divided into head and trunk regions. The head has a mouth at the tip and sometimes eyes, tentacles, or both. The trunk contains a straight intestine, reproductive organs, at least one pair of simple waste-filtering organs, and an anus (AY-nuhs). Muscles on the trunk run in the circular, lengthwise, and spiral directions. There is no body cavity. Some gastrotrichs have sticky tubes on the head or trunk.


Gastrotrichs live all over the world.


All gastrotrichs live in water. About one-half of all species live in the sea between sand grains on beaches and the continental shelf. Some species live in the deep sea. Freshwater gastrotrichs live on submerged or floating plants, drift in open water, or live between grains of sand.


Gastrotrichs eat algae, other protists, and bacteria. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves. Protists (PROH-tists) are one-celled living things that have a nucleus (NOO-klee-uhs), which is the control center of a cell.


Gastrotrichs glide by beating the hairlike fibers on their bellies and use muscles to change direction while gliding. Sea-dwelling species move toward and along solid objects such as sand or gravel and use sticky tubes to attach to the bottom. Some species use creeping movements like those inchworms make. Most gastrotrichs move away from light.

Gastrotrichs make both sperm and eggs. They place sperm in each other while mating. Fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development, takes place inside the body, but the embryos, or fertilized eggs, are released and develop outside the body. When they hatch, the young gastrotrichs look like small adults. There is no larva stage. A larva (LAR-vuh) is an animal in an early stage that changes form before becoming an adult.


Gastrotrichs may help beaches by eating washed-up waste, preventing decay and the odor that comes with it.


Gastrotrichs are not considered threatened or endangered.

NO COMMON NAME (Lepidodermella squamata): SPECIES ACCOUNT

Physical characteristics: Lepidodermella squamata (abbreviated as L. squamata) gastrotrichs are shaped like bowling pins and grow to a length of 0.007 inch (190 micrometers). The head is separated from the body by a short neck. The trunk has a forked tail and two sticky tubes. The body covering is made up of scales. Hairlike fibers are present on the sides of the head and in two rows on the belly.

Geographic range: L. squamata gastrotrichs live in the United States, Brazil, Uruguay, Japan, and much of Europe.

Habitat: L. squamata gastrotrichs live on plants in lakes, ponds, swamps, and streams. They also may live between grains of sand.

Diet: L. squamata gastrotrichs eat algae, bacteria, and waste.

Behavior and reproduction: L. squamata gastrotrichs glide slowly and are sensitive to blue light. The life cycle begins with development of eggs without fertilization. Up to four of these eggs are laid. Some develop quickly, but the eggs usually develop slowly and can survive drying out and freezing. A few days after hatching, the gastrotrich develops both female and male reproductive organs.

Lepidodermella squamata and people: L. squamata gastrotrichs are sold for use in laboratory studies.

Conservation status: L. squamata gastrotrichs are not considered threatened or endangered. ∎



Burnie, David. How Nature Works. Pleasantville, NY: Reader's Digest, 1991.

Cushing, Colbert E., and J. David Allan. Streams. San Diego, CA: Academic, 2001.

Reid, George K. Pond Life. New York: St. Martin's, 2001.

Web sites:

"Chaetonotus (Gastrotricha) Movies." Florida State University. (accessed on February 2, 2005).

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