1. Annelids
Chapter 35 B

2. About Annelids The term annelida means “little rings”
The rings refer to the many body segments

3. Characteristics This is a phylum with 15,000 species
All have bilateral symmetry
Like mollusks – they are coelomates

4. Characteristics Segmentation is their most distinguishing feature
Each segment has its own coelom
Allows different body parts to expand or contract independently
Provides an insurance policy against injury

5. Characteristics More distinguishing features:
Setae (external bristles)
Parapodia ( fleshy protrusions)

6. Class Oligochaeta
“Few Bristles”

7. Oligochaeta These annelids live in freshwater or in the soil
They do not have parapodia
They have very few setae ( “few bristles” )

8. Oligochaeta These annelids have more than 100 segments
Circular and longitudinal muscles line the body

9. Oligochaeta – digestive system
Earthworms ingest soil as they pass through it
Soil enters the pharynx to the esophagus

10. Oligochaeta Then from the esophagus to the crop
Temporary storage site
From the crop it moves to the gizzard
Mechanical break down using stones

11. Oligochaeta From the gizzard to the intestine
Nutrients absorbed
Waste proceeds through to the anus

12. Oligochaeta – circulatory system
Annelids have a closed circulatory system
The system contains 5 pairs of aortic arches
The arches link the dorsal to ventral blood flow

13. Oligochaeta – respiratory system
Mucus and a cuticle keep Annelids moist
They absorb O2 and CO2 directly thru the skin

14. Oligochaeta – excretory system
Annelids get rid of waste and excess water
with excretory tubules called nephridia
Each segment – except first three and last – have their own pair of nephridia

16. Oligochaeta – nervous system
The nervous system is a chain of ganglia
Ganglia connected to a ventral nerve cord
Branches carry impulses to each segment

17. Oligochaeta – reproduction
Earthworms are hermaphrodites
They are held together by setae and a film of mucus – during reproduction

18. Oligochaeta – reproduction
Their clitellum secretes the film of mucus
The clitellum is a thickened section on the body of an earthworm

19. Class Polychaeta
“Many Bristles”

20. About Polychaeta About two-thirds of all Annelids are here
They have antennae
They have specialized mouth parts
Most live in a marine environment
They are free-swimming predators

22. Class Hirudinea

23. About Hirudinea This is the smallest class of Annelids
These are the leeches
Most live in calm waters

24. About Hirudinea They have no setae or parapodia
They have anterior and posterior suckers

25. Annelids
Chapter 35 B
The End