1. Introduction to Annelids
Biology 11
Mrs. Trevelyan

2. Annelids 1. PRESCRIBED LEARNING OUTCOMES and VOCABULARY 2. VIDEOS:
Introduction to Insects (25 min)
3. TEXTBOOK PGS
Chp 28 pg

4. Overview…

5. Examples of Members:

6. 1. Unifying Characteristics
Annelida means “little rings”
Includes earthworms, leeches, marine worms
Bilateral symmetry, coelomate (have a true coelem)
More complex organisms- have 3 layers and organs
Segmented body parts separated by SEPTA
Have a closed circulatory system
Some have bristles called SETAE to help them move
Have well developed nervous system with brain and spinal cord
Sexual reproduction- some are hermaphrodites

7. 2. Three Major Classes Class Oligochaeta – Earthworm
Class Hirudinea – Leeches
Class Polychaeta - Marine worms 

8. Class Oligochaeta – Earthworm
Streamlined bodies for moving through soil
Few setae, allows for gripping soil
Live in soil or fresh water
As earthworms pass food & soil through intestines, nutrients are absorbed and indigestible matter passes out through anus as castings
Castings - enrich soil,
earthworms aerate soil

9. Class Hirudinea - Leeches
-external parasites with suckers on each end - suck blood & body fluids from host -most live in moist tropical habitats -secrete hirudin- an anticoagulant (keeps you bleeding) -medicinal uses (circulation, anti-clotting)

10. A close up of a leech

11. Class Polychaeta - Marine worms
includes: sandworms, bloodworms, & relatives
have paired paddle-like appendages with setae

12. 3. Structure 3 germ layers True coelom
Segmented tube body with 2 openings (mouth, anus)
Each segment is separated by septum, which are internal walls between each segment

13. Body segments may carry eyes, antennae, other sense organs, or be specialized for functions such as respiration.
Bristles called setae may be attached to each segment.
In marine worms setae may develop into parapodia

14. 4. Feeding and Digestion
In carnivorous species, the pharynx usually holds two or more sharp jaws that are used to attack prey. Ex. Leeches
video: leeches feeding
Annelids that feed on decaying vegetation have a pharynx covered with sticky mucus. Ex. Earthworms
video: earthworm feeding

15. An Earthworm’s Meal
In earthworms, the pharynx pumps food and soil into the esophagus.
The food then moves through the crop, where it can be stored.
It then moves through the gizzard, where it is ground into smaller pieces.

16. 5. Respiration Aquatic annelids often breathe through gills.
Land-dwelling annelids take in oxygen and give off carbon dioxide through their moist skin. Diffusion

17. 6. Circulation Have blood and blood vessels Have as many as 5-6 hearts
typically have a closed circulatory system, in which blood is contained within a network of blood vessels.

18. Many annelids have green blood

19. 7. Excretion
Kidney-like nephridia are excretory organs that filter fluid in the coelom.
Nephridia

20. 8. Nervous System
Most annelids have a well-developed nervous system consisting of a brain and several nerve cords.
Brain
Ganglia

21. Movement
Annelids have two groups of body muscles that function as part of a hydrostatic skeleton.
Longitudinal muscles
Circular muscles
Video: worm crawling

22. 9. Reproduction Most annelids reproduce sexually.
Earthworms are hermaphrodites. Two worms attach to each other, exchange sperm, and then store the sperm in special sacs

23. Reproduction cont’d
A clitellum is a band of thickened, specialized segments.
After eggs are fertilized in the ring, the ring slips off the worm's body and forms a protective cocoon.
Young worms hatch weeks later.

24. Earthworm Life Cycle

25. 10. Ecological Importance
Circulate soil and compost
Food source for many animals
Medicinal uses (leeches)