Characteristics
Some species of earthworms have a tongue-like lobe above the mouth called prostomium. The prostomium is actually a sensory device. Earthworms do not have a nose, eyes, ears, or hands to gather sensory information about their environment. Instead, they depend on their prostomium and sensory receptors in their skin to "feel" their way through the soil. Worms usually have a cylindrical, flattened, or leaf-like body shape and are often without any true limbs or appendages. 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.
Some worms reproduce sexually. Hermaphroditism, the condition in which a single individual possesses both male and female reproductive parts, is common in many groups of worms. Asexual reproduction, whereby new individuals develop from the body cells of another, also occurs in some worms.
Worm species differ in their abilities to move about on their own. Many species have bodies with no major muscles, and cannot move on their own—they must be moved by forces or other animals in their environment. Many other species have bodies with major muscles and can move on their own; they are a type of muscular hydrostat. Many species of worms are decomposers; they break down dead plants and animals to return nutrients to the soil. They have also been known to infiltrate households feeding on food in the early stages of its decomposition namely breads and cheeses.
Earthworms split into three different categories. The first are the surface dwellers, the Epigeic worms. Then there are the upper soil worms, the Endogeic worms. Finally,there are the deep burrowing species, the Anecic.
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