1. Phylum Annelida

3. Leeches

5. General Information Annelids are ringed, segmented worms
Examples include earthworms and leeches
Habitat: terrestrial, fresh water, marine
Have bilateral symmetry with 3 body layers (ectoderm, mesoderm, & endoderm)

6. 3 Unique Features Have a true coelom (body cavity) lined by mesoderm
Have externally visible body segmentation
Have a closed circulatory system

7. Coelom Located between the body wall and the intestine
Lined by mesoderm
Filled with fluid
Acts as a buffer between body muscles and the intestine (allows worm to move without putting pressure on the intestine)

8. Body Segmentation The body is divided into segments
Each segment contains a portion of the coelomic cavity
Each segment is separated internally by septa (membranes)

9. Class Polychaeta Polychaete worms Marine Flattened bodies
Body segments with paired paddle-like appendages (parapodia)

12. Class Oligochaeta Earthworms Have a few hairs Small head for burrowing
May have a saddle-like swelling (clitellum)

13. Class Hirudinea Leeches Often aquatic Bodies with suckers
Many are ectoparasites feeding on blood

14. Class Oligocheatea
Earthworms will be our representative organism for this Phylum

15. Earthworm Ingestion
Earthworms have a complete digestive system (one way digestive tract)
Food (organic material in the soil) enters through the mouth
The pharynx draws food into the mouth (suck in and swallows food)
Food moves through the esophagus to the crop where it is stored temporarily

16. Earthworm Digestion Food moves from the crop to the gizzard
Gizzard contains sand grains which help grind up food by muscular contractions
Food moves into the intestine where enzymes chemically digest (break down) food into particles small enough to be absorbed into blood
Intestine has a typhlosole which increases the surface area for nutrient absorption

17. Feeding and Digestion

19. Earthworm Elimination
Undigested food waste moves to the end of the intestine and exits through the anus

20. Earthworm Respiration
Gas exchange (O2 & CO2) happens via diffusion through the moist skin
Mucus glands secrete mucus to keep skin moist
O2 diffuses across the moist skin and into the capillaries and blood
O2 is carried by hemoglobin (Hb) in the blood

21. Earthworm Circulation
Earthworms have a closed circulatory system (blood is always contained in vessels)
Closed circulatory systems allow for more effective delivery of nutrients which allows for increased activity and size
Earthworms have 5 pairs of hearts which pump blood through the vessels

23. Earthworm Excretion
Excretory organs called nephridia filter excess H2O and nitrogenous wastes from the coelomic cavity of one segment
This waste passes through a long tube surrounded by blood vessels (much like our kidneys) and eventually exits through an excretory pore in the next segment
Excess water is reabsorbed into the blood vessels

25. Earthworm Sexual Reproduction
Earthworms are hermaphrodites (male & female on same individual)
2 earthworms cross-fertilize (exchange sperm)
Earthworms have a swelling called a clitellum which secretes a mucus cocoon into which fertilized eggs are deposited

27. Earthworm Asexual Reproduction
Earthworms are able to regenerate missing body parts

28. Earthworm Nervous System
Earthworms have a paired ventral nerve cord which swells into ganglia (a mass of nerve cell bodies acting as a primitive brain) at the head

29. Earthworm Locomotion
Uses longitudinal and circular muscles combined with the fluid pressure in the coelom and the setae (bristles) to help burrow and move
Contraction of the circular muscles of anterior (front) cause worm to lengthen
Paired setae (bristles) anchor worm to soil
Longitudinal muscles contract causing worm to shorten pulling it’s posterior (tail end forward)

31. Evolutionary Significance
Segmentation! Body segmentation lead to the ability to have specialized structures in the body plan of organisms.
Share common ancestor with the Arthropods
Closed Circulatory System – heart(s) and blood vessels
True Coelom – mesoderm lines the digestive tract