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Annelida: Exploring Diversity and Importance

Discover the characteristics, classes, feeding, reproduction, and systems of Annelids - Polychaeta, Oligochaeta, and Hirudinea - segmented worms with significant ecological roles.

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Annelida: Exploring Diversity and Importance

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  1. Today’s Objectives • Explore the diversity, success, body plans, organ systems and economic importance of phylum Annelida.

  2. Annelida Segmented Worms

  3. Main Characteristics • Bilateral symmetry • Metameric • Tagmatization • Protostomes • Triploblastic • Setae • Closed Circulatory System • Ganglia and Nerve Cords • Metanephridia

  4. Classes of Annelids • Polychaeta – Nereis, Arenicola • Oligochaeta – Lumbricus, Tubifex • Hirudinea - Hirudo

  5. Class Polychaeta • Mostly marine • Parapodia • Cuticle • 1st segment – prostomium • 2nd segment – peristomium

  6. Polychaeta Feeding • Most carnivorous • Some have venom • Gut is straight tube • Some are detritovores • Extract nutrition from sediment (or soil) • Gut has crop and gizzard • Many are filter feeders • Some can get food by diffusion

  7. Other polychaete Systems • Respiration by diffusion • 2-4 pairs of eyes on/near prostomium • Chemoreceptors • Statocysts • Metanephridium for excretion • Chloragogen tissue for protein metabolism

  8. Polychaete Reproduction • Can regenerate • Asexual reproduction • Budding • Fission • Sexual reproduction • Most fertilization external • Can have alternation of generations • Epitoke (sexual) vs. Atoke (asexual)

  9. Oligochaeta • Terrestrial, freshwater, some marine • Have a clitellum • For mucus secretion • Used in copulation • Used to form cocoons • No parapodia • Few setae

  10. Oligochaete Locomotion • Use circular and longitudinal muscles • Can use setae as anchors • Use hydrostatic pressure

  11. Oligochaete Feeding • Scavengers and/or detritovores • Path of food • Mouth • Pharynx • Crop • Gizzard • Stomach • Intestine

  12. Other Oligochaete Systems • Most ganglia fused • Reduced eyes • Sensitive to chemical or mechanical stimuli • Use metanephridia for excretion • Chloragogen tissue

  13. Oligochaete Reproduction • Hermaphroditic • Must line up clitella • Held together by mucus sheath • Cocoon formed • Fertilization occurs here • No larval stages • Some freshwater species asexual

  14. Hirudinea • Terrestrial, freshwater or marine • No parapodia • Secondary annuli on segments • Circular, longitudinal and oblique muscle layers

  15. Hirudinean Feeding • Many carnivorous • Small invertebrates • Body fluids • Mouth in the anterior sucker • Produce “hirudin” – anticoagulant

  16. Other Hirudinea Systems • Gas exchange by diffusion • Nervous system • Photoreceptors • Can sense temperature • Sensory papillae • 10-17 pairs of metanephridia for waste • Chloragogen tissue

  17. Hirudinea Reproduction • All monecious • All sexually reproducing • Have a penis for sperm transfer • Clitellum seen during breeding season • No larval stages

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