The Annelida phylum consists of the segmented worms. They lack a backbone and have bodies divided up into many segments. This phylum includes earthworms, leeches, and feather duster worms. Some species are terrestrial, while others are found in marine environments.
Animals in this phylum have segmented bodies. Most of the segments have the same internal organs. However, the forward and rear segments are slightly different. The forward segments have the mouth and brain. The rear segments have a growth area and an anus. Some annelids breathe through their skin. Others have gills. Some species reproduce asexually, but most reproduce sexually. Most annelids have a pair of body cavities (coelem) in each segment.
Within the phylum there are two main classes. These are the Polychaetes and the Clitellates. The Polychaetes includes the bristle worms. The Clitellates include the earthworms and leeches.
There are over 22,000 species in the phylum Annelida.
Annelids are found throughout the world. They may be terrestrial or aquatic in terms of their habitat.
Humans and Annelida
Many species of Annelida are important to human life. Earthworms and other terrestrial annelids loosen the soil and help fertilize it with their waste. Marine annelids also modify their environments by burrowing into the ocean bottom.
Historically, leeches were used for medicinal purposes – through blood letting. Today, some leeches are still used in some types of surgery.
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The Phylum Annelida, Earthlife.net.