1. Chapter 10: Phylum Platyhelminthes

2. Phylum Platyhelminthes
Contains over 34,000 animal species
Can range from 1 mm (or less) to 25 m (beef tapeworm)
Triploblastic Acoelomate (has organs)
Mesoderm is called the parenchyma (loose tissue that fills in the space between tissues, organs and the body wall.
Function of the parenchyma: skeletal support, nutrient storage, motility, may contain regenerative cells, oxygen storage, and transport of materials.

3. General Characteristics
Triploblastic acoelomate
Bilateral symmetry
Unsegmented
Incomplete gut
Somewhat cephalized
Monoecious
Protonephridia
Very simple nervous system

4. Class Turbellaria Free-living flatworms
Bottom dwellers in marine and freshwater environments
Named for the turbulence that their beating cilia create while swimming
Predators and scavengers
Mostly black, brown and gray
Some have bright colored patterns.

5. Class Turbellaria Ventral surface contains gland cells
Rhabdites- create a mucous sheath around the body
Adhesive glands-Attaches worm to a substrate
Releaser glands-secretes a chemical that dissolves the attachment
Glide over substrates using muscles and mucous secreted by the gland cells.

6. Class Turbellaria: Digestion/Nutrition
Digestive cavity varies from simple to highly branched
Pharynx-ingestive organ
Sensory cells help to detect food from a distance
Digestion
begins with enzymes
released by the
pharynx, then
phagocytosis occurs

7. Class Turbellaria: Respiration/Excretion
Respiration via diffusion across the body wall
Excretion (ammonia) via diffusion
Protonephridia
Regulates osmotic pressure in freshwater environments
Flame cells: specialized cells that are used to create a different pressure.

8. Class Turbellaria: Nervous System
Similar to nerve net
Statocyst
Detects the body position in terms of gravity
Cerebral ganglion (primitive brain) with neurons
Auricles
Sensory lobes (chemoreception)
Ocelli
Light sensitivity
Negative reaction

9. Class Turbellaria: Reproduction
Asexually
Fission (produce zooids)

10. Class Turbellaria: Reproduction
Sexually
Monoecious
Internal fertilization
Exchange sperm and release eggs (cocoon)

11. Class Trematoda The Flukes ~8000 species Wide, flat shape
Parasitic in vertebrates as adults
Feed on host cells or fragments (blood/body fluids)
Immature forms can be parasitic in vertebrates or invertebrates (or attached to plants).

12. Class Trematoda Epidermis called the tegument Glycocalyx
Adaptation to allow for a parasitic lifestyle
Outer layer is called the glycocalyx
Glycocalyx
Aids in transport of nutrients, gases and wastes across the body wall
Protects the fluke from the host’s immune system

13. Class Trematoda
Most flukes require at least two different hosts to complete their life cycles.
Adhesive organs:
Oral sucker (surrounds the mouth)
Acetabulum (middle of the body)
Important trematode parasites of humans:
Chinese Liver Fluke (requires 2 intermediate hosts: snail and fish)
Human eats raw or poorly cooked fish
Schistosome Blood Fluke

15. Class Cestoidea Tapeworms ~3500 species Endoparasitic
Two major endoparasitic adaptations
Loss of the mouth and digestive tract (absorb nutrients across the body wall)
Consist of repeating units called proglottids (each proglottid contains one or two complete sets of reproductive structures).

16. Class Cestoidea Body is divided into 3 regions: Scolex Neck Strobila
Contains the suckers and hooks
Tapeworm will use the scolex to attach itself to the intestinal wall of the host
Neck
Strobila
Consists of proglottids
Proglottids contain the reproductive organs
Newer proglottids are added as the tapeworm grows
Older proglottids mature as they move posteriorly from the neck and begin to produce eggs (gravid).

17. The testes mature before the eggs, so copulation generally occurs between different proglottids or between two different tapeworms (in the same host).
Gravid proglottids break free and are released into the host’s feces.