Worm, Worm

Invertebrate animals commonly called "worms" include annelids (earthworms), nematodes (roundworms), flatworms, marine polychaete worms (bristle worms), marine nemertean worm ("bootlace worms"), and insect larvae such as caterpillars, grubs, and maggots.

There are worms that live in freshwater, seawater, and even on the seashore.

Earthworms in general have been around for 120 million years, and are theorized to have evolved during the time of the dinosaurs. They enrich and aerate the soil; Charles Darwin found that worms turn over the top six inches (15 cm) of topsoil every 20 years. They lack a brain but have nerve centers (called ganglia); they also lack eyes but can sense light with photoreceptors. Worms are hermaphrodites (both sexes in one animal) but can cross fertilize.

In particular, many unrelated insect larvae are called "worms", such as the railroad worm, woodworm, glowworm, bloodworm, inchworm, mealworm, or silkworm.

Hence "helminthology" is the study of parasitic worms. When an animal, such as a dog, is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms.

Instead, they may have bristles or fins that help them move. A few have light-sensing organs. Worms vary in size from less than 1 mm (0.04 inch) in certain aschelminths to more than 30 m (100 feet) in certain ribbon worms.

Asexual reproduction, whereby new individuals develop from the body cells of another, also occurs in some worms.

Many species of worms are decomposers; they break down dead plants and animals to return nutrients to the soil.

Source: Wikipedia > Worm