Phylum Annelida | Biology for JAMB PDF Download

Introduction - Phylum Annelida

Phylum Annelida is a diverse group of segmented worms that belongs to the animal kingdom. These organisms are found in a variety of habitats, including marine, freshwater, and terrestrial environments. The name "Annelida" is derived from the Latin word "annellus," meaning a little ring, which refers to the characteristic body segmentation seen in these organisms.

Key Characteristics of Phylum Annelida:

• Body Segmentation: Annelids exhibit metamerism, which means their bodies are divided into repeating segments called metameres. Each metamere typically contains identical sets of organs, including muscles and nerves.
• Bilateral Symmetry: Annelids possess bilateral symmetry, meaning their bodies can be divided into two equal halves along a central axis.
• Coelom: Annelids have a true coelom, which is a fluid-filled body cavity located between the body wall and the gut. The coelom acts as a hydrostatic skeleton, providing support and aiding in movement.
• Complete Digestive System: Annelids have a complete digestive system, consisting of a mouth, pharynx, esophagus, intestine, and anus. This allows for efficient ingestion, digestion, and absorption of food.
• Closed Circulatory System: They possess a closed circulatory system, with blood contained within vessels. The circulatory system helps in the transport of oxygen, nutrients, and waste products throughout the body.

Examples of Annelids

• Earthworm (Lumbricus terrestris): Earthworms are common examples of annelids found in terrestrial environments. They play a vital role in soil ecology by burrowing through the soil, aiding in nutrient cycling and aeration.
• Marine Polychaetes: Polychaetes are annelids that inhabit marine environments. They display a wide range of adaptations and can be found in various marine habitats, such as coral reefs, sandy bottoms, and hydrothermal vents.
• Leeches: Leeches are another well-known group of annelids. They are found in freshwater habitats and possess a sucker at each end of their body. Leeches are known for their ability to feed on blood and are used in medicinal practices such as bloodletting.

Understanding the characteristics and examples of Phylum Annelida provides insights into the diversity of segmented worms and their ecological importance in different habitats.