Annelida - Kingdom: Animalia - SS1 Biology Lesson Note
Annelida is a phylum of segmented worms, commonly known as annelids. They exhibit a segmented body structure, with each segment containing repeated organs and structures. Annelids are found in various habitats, including marine, freshwater, and terrestrial environments.
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Here are some key features and characteristics of Annelida:
1. Body Structure: Annelids have a segmented body, divided into distinct repeating units called segments. Each segment usually contains a pair of bristles called setae, which aid in locomotion. The segments are separated by internal partitions called septa.
2. Coelom: Annelids have a well-developed coelom, which is a fluid-filled body cavity lined with mesodermal tissue. The coelom provides space for organ systems and allows for efficient movement.
3. Digestive System: Annelids possess a complete digestive system, including a mouth, pharynx, esophagus, intestine, and anus. They exhibit various feeding strategies, ranging from filter feeding to predation.
4. Circulatory System: Annelids have a closed circulatory system, meaning blood is confined within vessels. They have a muscular, tubular heart that pumps blood throughout the body. The circulatory system facilitates the transport of oxygen, nutrients, and waste products.
5. Respiration: Annelids respire through their body surface or specialized structures. Some aquatic annelids have gills for extracting oxygen from water, while others exchange gases directly through their skin. Terrestrial annelids have evolved adaptations to breathe in oxygen-rich environments.
6. Nervous System: Annelids possess a well-developed nervous system. They have a paired ventral nerve cord that runs the length of the body and a series of ganglia (nerve cell clusters) in each segment. Sensory structures such as eyespots and tactile receptors are present in some species.
7. Reproduction: Annelids exhibit diverse reproductive strategies. Most species are sexually reproducing, with separate sexes (male and female). Fertilization may be internal or external, and some species display elaborate courtship behaviors. Some annelids also reproduce asexually through fragmentation or budding.
8. Habitat and Diversity: Annelids inhabit a wide range of environments, including marine sediments, freshwater habitats, and damp soil. The phylum Annelida encompasses a diverse array of organisms, including familiar examples such as earthworms, leeches, and marine polychaetes.
9. Ecological Importance: Annelids play vital roles in ecosystems. Earthworms, for instance, contribute to soil fertility and structure through their burrowing and feeding activities. Some annelids are also important food sources for other organisms, while others serve as parasites or predators.