Annelida
Sign in to saveThe annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.
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Annelids, also called segmented worms, are a diverse group of animals that includes familiar species like earthworms, ragworms, and leeches, with over 22,000 known species alive today. They matter because they have successfully adapted to live in many different environments—from ocean floors and tidal zones to freshwater and moist soil—making them important parts of ecosystems worldwide.
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Article
21 sectionsContents
- Classification and diversity
- Distinguishing features
- Description
- Segmentation
- Body wall, chaetae and parapodia
- Nervous system and senses
- Coelom, locomotion and circulatory system
- Respiration
- Feeding and excretion
- Reproduction and life cycle
- Asexual reproduction
- Sexual reproduction
- Ecological significance
- Interaction with humans
- Evolutionary history
- Fossil record
- Internal relationships
- External relationships
- Notes
- References
- External links
The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.
The annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Most textbooks still use the traditional division into Polychaetes (almost all marine), Oligochaetes (which include earthworms) and Hirudinea (leech-like species). Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a "super-phylum" of protostomes that also includes molluscs, brachiopods, and nemerteans.