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Phylum Annelida

Phylum Annelida. The Segmented Worms. Symmetry and Body Plan. Bilateral symmetry Tube-within-a-tube plan Separate mouth and anus Coelomate (true body cavity) Segmented (repeated body features). Digestion and Excretion. Digestion : Complete digestive tract.

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Phylum Annelida

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  1. Phylum Annelida The Segmented Worms

  2. Symmetry and Body Plan • Bilateral symmetry • Tube-within-a-tube plan • Separate mouth and anus • Coelomate (true body cavity) • Segmented (repeated body features)

  3. Digestion and Excretion Digestion: • Complete digestive tract. • Pharynx, esophagus, crop, gizzard, intestine, and peripheral organs. Excretion: • Dedicated excretory tubes called nephridia. • Found in most segments.

  4. Respiration and Control Respiration: • Gases diffuse across the body wall. • Closed circulatory system with hearts and blood vessels move gasses. Nervous System: • Anterior brain with a ventral nerve cord. • Ganglia (bundles of nerve cells) in each segment.

  5. Nervous System

  6. Movement • Possess longitudinal and circular muscle in each segment. • Allows a range of movement. • Many possess setae – small bristles that help in movement and adhesion.

  7. Reproduction (Based on Oligochaetaonly) • Hermaphroditic (possess both male and female gonads) • Worms lay parallel to each other in opposite directions and exchange sperm. • After separation, form a slime tube which combines sperm and eggs. • Slime tube later produces a cocoon.

  8. Earthworm Reproduction

  9. Annelid Classes • Class Polychaeta – marine worms • Class Oligochaeta – earthworms • Class Hirudinea – leeches

  10. Class Polychaeta • Have setae. • Usually have separate genders. • Have “feet”-like structures called parapodia • Also used as a surface for respiration. • Examples: tube worms (filter feeders) and Nereis (aka “clam worms” – predators)

  11. Polychaeta

  12. Class Oligochaeta • Have fewer setae than polychaeta. • Head isn’t obvious. • Respiration occurs across body wall. • Generally saprophytic or herbivorous. • Very clearly segmented • Body rings and septa on external surface • Ganglia in each segment • Nephridia (excretory organs) in each segment. • Branches of circulatory system in each segment.

  13. Oligochaeta

  14. Class Hirudinea • Usually live in fresh water. • Ectoparasites – “eat” host from the outside (not the inside like other parasites). • Lack setae (no bristles for movement). • Attack hosts with an anti-coagulant saliva (prevents wound from closing).

  15. Hirudinea

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