Clitellata
Clitellata is a subclass of the annelid worm phylum, encompassing over 8,000 species of earthworms, leeches, and a few other related groups. They are distinguished by a distinctive band of thickened epithelium called the clitellum, which plays a role in reproduction. Clitellates are found in a wide range of habitats, from freshwater and marine environments to terrestrial ecosystems.
Common Names
Clitellates are commonly known by several names, including earthworms, leeches, and aquatic worms. These names reflect the diversity of this group, encompassing a range of morphologies and ecological roles.
Characteristics
Clitellates are characterized by several key features, including:
- A segmented body, with each segment usually possessing bristles called setae
- A closed circulatory system
- A well-developed nervous system with a brain and ventral nerve cord
- The presence of a clitellum, a thickened band of tissue that secretes a cocoon for eggs
- Direct development, meaning there is no larval stage
Environments
Clitellates inhabit a wide variety of environments, including:
- Terrestrial: Earthworms are found in soil, playing a crucial role in decomposition and nutrient cycling.
- Freshwater: Some clitellates, such as leeches, inhabit freshwater lakes, ponds, and streams.
- Marine: A few species of clitellates are found in marine environments, particularly in coastal areas.
References
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