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Annelida Meaning
The annelids are a large phylum of invertebrates that includes the earthworms, leeches, and ragworms. They are characterized by their segmented bodies and the presence of bristles, or setae, on their surface. The annelids are a diverse group, with over 22,000 species currently described.
The word Annelida is derived from the Latin word annelus, meaning “little ring”. This is in reference to the segmented body of annelids, which appears as a series of rings. Annelids are a diverse phylum of invertebrates that includes earthworms, leeches, and ragworms. They are typically characterized by a segmented body, a head with sensory organs, and a clitellum (a band of tissue that secretes the egg case). Annelids are important decomposers and play a key role in nutrient cycling.
Classification of Annelida
There are three main classes of annelids:
- Polychaeta: these are the marine worms, and include the common earthworm.
- Oligochaeta: these are the smaller, terrestrial worms, such as the common garden worm.
- Hirudinea: the leeches.
General Characteristics of Annelida
Annelida are a phylum of invertebrate animals that are characterized by their segmented bodies. They are typically small animals, and can be found in both marine and freshwater environments. Annelida have a coelom, a fluid-filled body cavity that surrounds the organs, and a closed circulatory system. They also have a nervous system with a brain, and a pair of ventral nerve cords. Annelida typically have a pair of bristles, or setae, on each segment of their body. These setae help the animals move through their environment.
Types of Annelids
There are three types of annelids: polychaetes, oligochaetes, and hirudinea.
- The polychaetes are the most diverse and abundant type of annelid. They are marine animals with a long, flexible body and many bristle-like appendages.
- The oligochaetes are also marine animals, but they have a short, stocky body and a few short appendages.
- The hirudinea are the only type of annelid that is not marine. They are the leeches, and they live in freshwater and moist terrestrial habitats.
