Annelids are invertebrates consisting of over 17,000 species of worms including ragworms, earthworms, and leeches. Annelids can be found in moist and wet earth, as well as marine and freshwater environments. Many annelids, such as leeches, are considered parasites.
Annelids range in size from microscopic worms to the Australian Giant Gippsland Earthworm measuring up to 10 feet long. Annelid bodies are long, narrow, and tubular in shape, with multiple segments divided by ring-like constrictions. The front segment contains the brain, mouth and sensory system. The rear segment contains the anus. Some middle segments contain organs such as the circulatory system, digestive system, and nervous system. Segments grow one at a time as the annelid grows older.
Most annelids have radial and circular muscles in the body segments. These muscles provide functions such as circulating blood through blood vessels, digesting food, and providing locomotion. Many annelids move by peristalsis, that are muscle contractions and expansions that sweep along the body like a wave. This allows the annelid to crawl or swim. Other annelids move by whip-like movements of their body.
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