1. Phylum Annelida
Leech
Nereis
Earthworm
The Segmented Worms

2. Are There Many Kinds of Annelids??
15,000 species of annelids can be divided into three major groups
Polychaeta
Oligocheata
Hirudinea

3. What Are Annelids? General Characteristics
Bilateral symmetry
Definate anterior / posterior ends
Distinguishable dorsal / ventral side
True tissue / organ level of organization
Segmented bodies
The distinguishing feature of all annelids
Annelida = “little rings”
Range in size
< 1mm up to 3 meters!!
Eg. giant Australian earthworm

4. The Internal Structure of Annelids
Complete digestive tract
Several specialized regions
Circulatory system
Closed vessels
Blood containing hemoglobin
Nervous system
Brain-like structure
Reproductive structures
Ovaries and testes

5. All Annelids Are Coelomates . . .
They have a true body cavity
Coelom is lined with mesoderm cell layer
“Tube-within-a-tube” body plan
Outside tube
Body wall
Inside tube
Digestive tract

6. Annelids are the simplest animals to have a true coelom!

7. What happens to the “stuff” annelids eat?!?
Specialized regions aid in digesting the organic matter in soils ingested
CROP
Temporarily stores food
GIZZARD
Thick walled organ which grinds food

8. Nereis . . . The Hunter Tentacles Marine Sandworm Carnivorous
Found at tide level
Carnivorous
Feeds on small animals
Distinct anterior segment
Prostomium
2 short tentacles + 2 palps
2 pairs of small eyes
Peristomium
4 pairs of tentacles surrounding mouth
Figure 32-14,
Pg. 698
Palps

9. How does the pharynx work??
The pharynx is extended out of the mouth
Pointed claw-like jaws capture prey
Pharynx pulls food back through mouth
Food moves into intestine where digestion begins
Pharynx
Jaw

10. These Guys Can Move!
Parapodia
Nereis have structures allowing them to swim AND creep over sand
Parapodia
Paddle-like extensions
Setae
Bristle-like structures
Setae

11. Reproduction in Annelids
Oligochaeta & Hurudinea
Hermaphrodites
Cross-fertilization
Internal fertilization
Polycheata
Separate sexes
External fertilization
Gametes are released through excretory organs
Free-swimming larva

12. Earthworms Create a Cocoon!
Clitellum : sperm are stored temporarily until a mucus cocoon is created to protect the fertilized eggs!

14. Leeches: the ecto-parasite!
Feed on the blood of their prey
Hirudin
Enzyme which prevents blood clotting
The jaws break through the host’s skin
Blade-like jaws make incision

15. Two Evolutionary Innovations
The presence of a true coelom
Provides support
Acts as a hydrostatic skeleton
Room for organ development
Advancements in locomotion
Not the dance!!!! Motility!!!
Segmentation of the body
Specialization of body regions
Feeding and sensory input, motility
Modification of various segments for different functions

16. Worms today. . . Mollusks tomorrow!
Until then . . .
Be kind to your neighborly annelid . . .
You may depend on one someday!