ROUNDWORMS: Adenophorea

PHYSICAL CHARACTERISTICS

The size of roundworms ranges from microscopic to as long as 3.3 feet (1 meter). Most roundworms have a hard, sharp spear on their head, and some have bristles on the head. The body of roundworms is protected by a flexible but strong, grooved body covering. A layer beneath this covering releases fluids that harden to form the covering. The body has three tissue layers and a fluid-filled false body cavity, meaning the cavity is between the inner and middle layers rather than the middle layer and the outer layer, as it is in complex animals. The sensing system of roundworms is made up of holes behind, or in some cases on, the lips.

GEOGRAPHIC RANGE

Roundworms live all over the world.

HABITAT

Roundworms live in water and soil everywhere except the desert. A few species are parasites of plants and animals. Parasites (PAIR-uh-sites) are animals or plants that live on or in other animals or plants, or hosts, without helping them and usually harming them.

DIET

Most roundworms eat bacteria, fungi, and tiny growths in the soil. The parasite species feed on blood, body fluids, intestinal contents, and mucus in their hosts.

BEHAVIOR AND REPRODUCTION

Roundworms move their spear in and out of their prey, puncturing the cells and emptying the contents. Most species of roundworms have two sexes, but in a few species the worms make both eggs and sperm. Fertilization (FUR-teh-lih-ZAY-shun), or the uniting of egg and sperm to start development, takes place inside the females, who then lay the eggs.

ROUNDWORMS AND PEOPLE

Roundworms that infect people can cause disease and death. Roundworm plant parasites damage crops. Roundworms that are not parasites help keep soil healthy, which helps the growth of crops. It may be possible to control mosquitoes with roundworms that kill mosquito larvae. Larvae (LAR-vee) are animals in an early stage that change form before becoming adults.

THAT'S A LOT OF WORMS

Nematodes (NEE-muh-toads), the group that includes roundworms, are second only to insects as having the largest number of animals on earth. Scientists estimate the total number of nematode species is eighty thousand to one million. The total number of species of roundworms is estimated to be about twelve thousand.

CONSERVATION STATUS

Roundworms are not considered threatened or endangered.

NO COMMON NAME (Desmoscolex squamosus): SPECIES ACCOUNTS

Physical characteristics: Desmoscolex squamosus worms have a small body that is tapered at both ends. Females are longer than males. The body covering has about 70 rings that have a row of holes. Bristles on the body are arranged in pairs. The head is wider than it is long and has a wide front end. The tail has two main rings, and females also have two partial rings.

Geographic range: Desmoscolex squamosus (abbreviated as D. squamosus) was discovered in southeastern Africa, but scientists do not know where else it lives.

Habitat: D. squamosus worms live mainly in the sea, but some live in freshwater and soil.

Diet: Scientists do not know what D. squamosus worms eat.

Behavior and reproduction: Scientists do not know how D. squamosus worms behave. They have two sexes, and fertilization takes place inside the female's body.

Desmoscolex squamosus and people: D. squamosus worms have no known importance to people.

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

NO COMMON NAME (Mermis nigrescens): SPECIES ACCOUNTS

Physical characteristics: Mermis nigrescens worms are free living as adults. As larvae they are parasites that infect the body cavity of grasshoppers. These worms are thin and 2 to 8 inches (5 to 20 centimeters) long. Females are longer than males. Adult females are reddish brown at the front.

Geographic range: Mermis nigrescens (abbreviated as M. nigrescens) worms live in the British Isles, Europe, and North America. Specific distribution map not available.

Habitat: While they are larvae, M. nigrescens worms live mainly in grasshoppers and locusts but may also infect other insects. Once they burrow out of a host, the larvae dig into the soil, where they transform into adults.

Diet: M. nigrescens larvae feed on nutrients in their host. The free-living adults do not eat, so the worms must gain all of their nutrients while in the insect host.

Behavior and reproduction: Adult M. nigrescens worms easily climb plants, especially during rainy seasons. Females may stay in the soil for several years before coming out to lay eggs on grass and plants, which are then eaten by grasshoppers. Even though they sometimes move toward light, the worms die if they receive continued exposure to direct sunlight.

After the eggs hatch, M. nigrescens larvae bore through the host insect's intestinal wall into its body cavity and feed on the host's nutrients. Many worms can infect the same grasshopper. By late summer, the grasshopper is packed with the parasites and dies. The larvae leave the dead insect's body, and the worms spend the rest of their lives in the soil transforming into adults and growing to reproductive age.

Mermis nigrescens and people: Because the larvae kill their hosts, it may be possible to use M. nigrescens worms to control grasshoppers, which harm crops.

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

FOR MORE INFORMATION

Books:

Aaseng, Nathan. Invertebrates. New York: Venture, 1993.

Niesen, Thomas M. The Marine Biology Coloring Book. 2nd ed. New York: HarperResource, 2000.

Web sites:

"Nematodes: Worms of the World." Medical Laboratory Observer.http://www.findarticles.com/p/articles/mi_m3230/is_1_33/ai_69759773 (accessed on February 2, 2005).