1. Phylum Annelida
The Segmented Worms

2. Classes of Annelida Class Polychaeta (fanworms, clam worms)
Class Oligochaeta (earthworms)
Class Hirudinea (Leeches)
Classes not covered
Class Branchiobdellida
Class Acanthobdellida

3. General Characteristics
Annelids are to be found in marine, freshwater, and terrestrial habitats
The body is vermiform, bilaterally symmetrical, and segmented
Each segment is separated from contiguous ones by a transverse septum
The body is triploblastic with a well developed coelom
The body is covered with a flexible non-chitinous cuticle

4. General Characteristics
Most forms have setae, hard, bristle-like chitinous structures
Digestive system is complete
Circulatory system is closed,
Excretory system typically consists of a pair of nephridia per segment

5. Typical Arrangement of Segments

6. Feather Duster worms, Clam worms, Christmas Tree worms
Class - Polychaeta
Feather Duster worms, Clam worms, Christmas Tree worms

7. General Characteristics
Mostly marine and free-living
Many setae, on fleshy lateral outgrowths of the body wall known as parapodia
Well developed head bearing appendages
Sexes separate, with a free-swimming trochophore larva

9. Nereis

10. Parapodia
Parapodium

11. Figure 17.03d

12. Some Polychaets

13. Figure 17.co

14. Figure 17.02a

15. Figure 17.02b

18. Figure 17.09

19. Earthworms and Freshwater Worms
Class Oligochaeta
Earthworms and Freshwater Worms

20. General Characteristics
Are terrestrial with a few freshwater species
Have few setae
No parapodia
No distinct head appendages
Clitellum present
Hermaphrodites, with copulation required
Eggs are deposited in a cocoon and development is direct

21. Figure 17.12a

23. Earthworm Dissection

24. Earthworm Dissection

26. Figure 17.12c

27. Figure 17.14

28. Figure 17.15

29. Figure 17.17

30. Some Oligochaets

32. Figure 17.18b

33. Figure 17.18c

34. Figure 17.18d

35. Figure 17.17g

36. Class Hirudinea

37. General Characteristics
Ectoparasites, not all - many feed on organic debris
Usually dorso-ventrally flattened with fixed number of body segments (34)
No setae or parapodia
Clitellum present only during reproduction
Two suckers – anterior and posterior

38. Figure 17.20