1. Phylum Annelida!

2. 9000 species in the phylum - earthworms only 1!
Phylum Annelida
9000 species in the phylum - earthworms only 1!
Live everywhere in the world (sea and land)
Latin word annulus means little ring
Size ranges from less than ½ mm to 6 m long (giant earthworm of Australia)
(video on next slide)
Coelomates

4. General Characteristics: 1. Segmented bodies

5. 2. Bilateral symmetry

6. 3. True body cavity is partitioned by structures called septa.

7. 4. The organs of the digestive, nervous, and circulatory systems penetrate the septa and run the length of the body.

8. 5. One way digestive tract is divided into several well developed organs: pharynx, esophagus, crop, gizzard, and intestine.

10. Circulatory System!!
The circulatory system is closed.

11. It contains a dorsal and ventral blood vessel, connected by 5 aortic arches just above the esophagus.
The dorsal blood vessel carries blood from the tail to the head, while the ventral one carries the blood back toward the tail.

12. Cephalization!!
The brain is small and is located under the pharynx. A ventral nerve cord extends from the brain and runs the length of the body. In each segment it swells to form a structure called a ganglion.

13. 1. Brain
2. Ventral nerve cord
3. Ganglion

14. Waste removal Solid waste exits via anus
Nitrogenous waste is removed from the body by structures called nephridia.

15. Each segment contains 2 nephridia except the first 3 and the last one.
Therefore an earthworm with 78 segments has how many nephridia??
148

16. Reproduction Earthworms are hermaphroditic.
(found in the clitellum which is segments 32-37) .

17. Locomotion
Their muscular system contains both circular and longitudinal muscles. As the circular muscles contract they elongate the body, while the longitudinal muscles shorten it.

18. Setae, small bristle-like hairs, extend from the body walls and act as anchors as worm moves. There are 4 pair of setae per segment. Therefore the same earthworm with 78 segments has how many Setae??
312

19. The Skin - No respiratory organs - breathe through moist skin.
- Contain a thin water proof layer called the cuticle.
- No respiratory organs - breathe through moist skin.

20. The Body
No skeleton other than the hydrostatic one formed by the fluid filled body cavity.