Characteristics of phylum Annelida
1. Segmented body: Annelids have a body divided into distinct segments called metameres, which are separated by septa.
2. Coelom: Annelids have a true coelom, a fluid-filled body cavity surrounded by mesoderm.
3. Circular and longitudinal muscles: Annelids have well-developed circular and longitudinal muscles in each segment, allowing for precise movement and control over body shape.
4. Chaetae: Many annelids have bristle-like structures called chaetae or setae on their body segments, which help with movement and burrowing.
5. Bilateral symmetry: Annelids exhibit bilateral symmetry, with a body plan that is mirror-image on either side of a central axis.
6. Closed circulatory system: Annelids have a closed circulatory system, with blood contained within vessels and pumped by a heart.
7. Nervous system: Annelids have a well-developed nervous system, with a ventral nerve cord and segmental ganglia in each body segment.
8. Reproduction: Annelids are mostly dioecious, meaning they have separate male and female individuals. They reproduce sexually, typically by releasing sperm and eggs into the water for external fertilization.
9. Habitat: Annelids are found in a variety of aquatic and terrestrial habitats, including marine environments, freshwater lakes and rivers, and moist soil.
10. Ecological significance: Annelids play important roles in nutrient cycling and soil health, as well as serving as food sources for other animals. Some annelids, such as earthworms, are also vital for agriculture by improving soil structure and fertility.