1. Unsegmented worms

2. 1. Phylum Platyhelminthes
Otherwise known as FLATWORMS
Characteristics:
- bilateral symmetry
- cephalization (development of nervous tissue at “head” end)

3. Free Living Flatworm (planaria)

4. Physiological Characteristics
Feeding & Digestion
Some are carnivores (suck food in at pharynx, branches into gastrovascular cavity
Enzymes in cavity break down food which diffuses into body cells
Some are parasites (feed on blood/tissue or host’s digested food)
Circulation & Respiration
Diffusion of O2 & CO2 across epidermal cells
Flame cells help get rid of excess water
Flame cells empty into tiny pores

5. More…
Nervous System
Free living worms have a “head” region & cephalization & primitive brain
Long nerve cords (2) run down sides of body
Ocelli sense light & dark
Parasitic flatworms DO NOT have nervous tissue
Locomotion (free living)
Cilia in epidermal cells
Muscle cells  allow for twisting & turning
Reproduction
Most are hermaphrodites (both male & female)
Sexual: between 2 worms (egg fertilized by sperm)
Asexual: binary fission

6. Class Turbellaria Example: Planarians, “cross eyed” freshwater worms
Features: Flatworms; live in a variety of environments (land, fresh water, oceans)

7. Class Trematoda Example: Flukes (ex. Blood flukes)
Features: Parasitic (internal or external); complex life cycle often involving several hosts
Reproduce sexually or asexually
Many are hermaphrodites

8. Class Cestoda Example: Tapeworm
Features: Parasitic (most live in intestines of host)
Scolex (head) contains suckers to embed in intestinal wall
Absorbs nutrients from host

9. Fun with Flukes!

10. 2. Phylum Nematoda Otherwise known as ROUNDWORMS
Simple digestive system (mouth  intestines  anus)
Range in size
Most are free living; some parasitic

11. Physiological Characteristics
Feeding & Digestion
Long tube (mouth  anus)
Many are carnivores, although some feed on decaying plant material
Circulation & Respiration
Diffusion; transfer of nutrients & gases internally also through diffusion

12. More… Nervous System GANGLIA in “head” region
Long nerves run down length of body allow for movement
Examples: hookworms, Ascaris (parasitic intestinal worm)