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Phylum Annelida

Explore the world of annelids, with over 15,000 species divided into main groups - Polychaeta, Oligochaeta, Hirudinea. Discover their features, internal structure, and fascinating behaviors like in Nereis, the sandworm. Learn about reproduction, movement, and their significance in nature.

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Phylum Annelida

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  1. Phylum Annelida Leech The Segmented Worms Nereis Earthworm

  2. Are There Many Kinds of Annelids?? • 15,000 species of annelids can be divided into three major groups Polychaeta Oligocheata Hirudinea

  3. What Are Annelids?General Characteristics • Bilateral symmetry • Definate anterior / posterior ends • Distinguishable dorsal / ventral side • True tissue / organ level of organization • Segmented bodies • The distinguishing feature of all annelids • Annelida = “little rings” • Range in size • < 1mm up to 3 meters!! • Eg. giant Australian earthworm

  4. The Internal Structure of Annelids • Complete digestive tract • Several specialized regions • Circulatory system • Closed vessels • Blood containing hemoglobin • Nervous system • Brain-like structure • Reproductive structures • Ovaries and testes

  5. All Annelids AreCoelomates . . . • They have a true body cavity • Coelom is lined with mesoderm cell layer • “Tube-within-a-tube” body plan • Outside tube • Body wall • Inside tube • Digestive tract

  6. Annelids are the simplest animals to have a true coelom!

  7. What happens to the “stuff” annelids eat?!? • Specialized regions aid in digesting the organic matter in soils ingested • CROP • Temporarily stores food • GIZZARD • Thick walled organ which grinds food

  8. Nereis . . . The Hunter Tentacles • Marine Sandworm • Found at tide level • Carnivorous • Feeds on small animals • Distinct anterior segment • Prostomium • 2 short tentacles + 2 palps • 2 pairs of small eyes • Peristomium • 4 pairs of tentacles surrounding mouth Figure 32-14, Pg. 698 Palps

  9. How does the pharynx work?? • The pharynx is extended out of the mouth • Pointed claw-like jaws capture prey • Pharynx pulls food back through mouth • Food moves into intestine where digestion begins Pharynx Jaw

  10. These Guys Can Move! Parapodia • Nereis have structures allowing them to swim AND creep over sand • Parapodia • Paddle-like extensions • Setae • Bristle-like structures Setae

  11. Reproduction in Annelids • Oligochaeta & Hurudinea • Hermaphrodites • Cross-fertilization • Internal fertilization • Polycheata • Separate sexes • External fertilization • Gametes are released through excretory organs • Free-swimming larva

  12. Earthworms Create a Cocoon! Clitellum : sperm are stored temporarily until a mucus cocoon is created to protect the fertilized eggs!

  13. Leeches: the ecto-parasite! • Feed on the blood of their prey • Hirudin • Enzyme which prevents blood clotting • The jaws break through the host’s skin • Blade-like jaws make incision

  14. Two Evolutionary Innovations • The presence of a true coelom • Provides support • Acts as a hydrostatic skeleton • Room for organ development • Advancements in locomotion • Not the dance!!!! . . . Motility!!! • Segmentation of the body • Specialization of body regions • Feeding and sensory input, motility • Modification of various segments for different functions

  15. Worms today. . . Mollusks tomorrow! Until then . . . Be kind to your neighborly annelid . . . You may depend on one someday!

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