1. Phylum Annelida
Segmented Worms

2. Phylum Annelida Metameric Body Plan Bodies are divided into segments
Separated by septa
Each segment has own excretory, nervous and circulatory structures
Flexible support and efficient locomotion

3. Characteristics Most complex of all worms Triploblastic, coelomates
Bilateral symmetry
More complex
Closed circulatory system

4. Characteristics Two sets of muscles Paired epidermal setae (bristles)
Circular and longitudinal
Paired epidermal setae (bristles)
Ventral side
Used in movement

5. Class Polychaeta “many bristles” ~5300 species Mostly marine
Largest group
Burrow into sea floor or live in reefs or tubes
Carnivores or filter feeders
Lateral extensions called parapodia with numerous setae
Respiratory gases diffuse across the body wall

6. Reproduction Remarkable regeneration Asexual reproduction
Some have break points that allow worms to sever themselves when a predator grabs them
Lost segments are later regenerated
Asexual reproduction
Budding or transverse fission
Sexual reproduction (most common)
Dioecious
Epitokes

7. Class Clitellata
Characterizes organisms based upon clitellum and few or no setae
Subclass Oligochaeta
Earthworms
Subclass Hirudinea
Leeches

8. Subclass Oligochaeta “few hairs” ~3000 species
Freshwater/terrestrial habitats
Lack parapodia and have fewer, shorter setae
Earthworms

9. Characteristics Mostly live in terrestrial environments
Most have identical segments
Specialized segements (clitellum)
Reproduction
Moves by anchoring setae then contracting circular muscles

10. Digestion Takes in soil through pharynx (acts as a pump)
Soil moves down esophagus to crop (storage)
Moves to gizzard (crushing/grinding)
Moves to intestine, absorption and digestion occurs through folds in walls
Solid waste out through anus
Valuable to gardeners and farmers
Break up soil, aerate, and add nutrients (Nitorgen)

11. Circulation Closed circulatory system
Blood circulates through series of vessels
Blood absorbs molecules and carries them through dorsal vessel to five pairs of “hearts”
“Hearts” pump blood into main ventral blood vessel and smaller vessels carry blood to body.

12. Respiration and Excretion
Take in O2 and give of CO2 by diffusion through skin.
Must remain moist (not too wet or dry)
Eliminate liquid wastes through ciliated tubes called metanephridia (2 per segment)
Chloragogen tissue (acts like a liver)
Amino acid metabolism, converts ammonia to urea
Converts excess carbs into glycogen and fat (store energy)

13. Nervous Control
Can respond rapidly due to concentration of nerves called cerebral ganglion (anterior end).
Connected to rest of body by ventral nerve cord
Ganglion connects each segment to cord
No external eyes or ears
Receptors in skin will enable reactions (light, sound, chemical)
Active mainly at night
Giant Fibers
Mediate an escape response
Responds to stimulus from either end of worm
Initiates “anchor” and longitudinal muscles contract to quickly pull worm away from stimulus

14. Reproduction Hermaphroditic
Female structures anterior, male structures posterior
Two worms exchange sperm
Mucus secretion from clitella holds them together
Sperm stored in seminal receptacle until just before eggs are laid
Clitellum forms a cocoon for the deposition of sperm and eggs
Fertilization occurs in the cocoon
Ends are sealed, deposited in soil, hatches in 1-3 weeks

15. Subclass Hirudinea ~500 species Leeches
Predators (feed on small invertebrates or feed on body fluids)
34 segments, reduced clitellum (only during reproduction)
Freshwater (some are marine or terrestrial)
Do not have setae

16. Characteristics Flat and tapered body with suckers on each end
Attach with anterior suckers
Three sharp jaws to pierce host skin
Secrete “hirudin” that prevents hosts’ blood from clotting
Reproduce sexually (monoecious)

17. Interesting Facts Used to be used to “detoxify” blood Plastic surgery
Thought leeches removed toxins
Plastic surgery
Used to increase blood flow which keeps tissue alive long enough for surgery, re-attachment or tissue lifting