1. Flatworms Phylum: PLATYHELMINTHES

2. VS.

3. Class Turbellaria includes: Planarians

4. Class Cestoda Includes: Tapeworms

5. Class Trematoda Includes: Flukes

7. II. Body Plan/Structure
Flatworms demonstrate a bilaterally symmetrical body plan
They are dorsoventrally flattened and lack a skeleton

8. II. Body Plan/Structure con’t
They have a highly branched gastrovascular cavity .
There is only one opening which serves the function of both the mouth and anus (not excretion)

9. They have three germ layers:
Ectoderm: Outside
Endoderm: Inside
Mesoderm: Middle layer of tissue between the ectoderm and the endoderm
Though Flatworms have three germ layers they are acoelomates and have no body cavity

11. Flatworms are also the most primitive organisms to show cephalization.
Flatworms do have true organs and primitive organ systems that are used for digestion and excretion
Flatworms are also the most primitive organisms to show cephalization.
The head region of Flatworms contains a concentration of nerve tissue called ganglia (singular=ganglion) that resembles a primitive brain.

12. Cephalization

13. They have two nerve cords that run from the ganglia in the head region along the ventral side of the worm to the tale region
In the head region of Flatworms are two eye-spots
They also have lobes on the side of their head called auricles

14. Auricles

15. Feeding
Flatworms have a mouth/anus which is connected to the gastrovascular system through a long muscular pharynx.
Small invertebrates or the remains of dead animals are taken into the mouth/anus by the muscular pharynx

16. The food is then digested in the highly branched gastrovascular cavity
The nutrients moves from the gut into the body cells by diffusion

17. Respiration
Respiration occurs by diffusion

18. Internal Transport
Nutrients and oxygen in the gut are simply absorbed into the body cells by the process of diffusion

19. Excretion
Most undigested food is released directly out of the anus/mouth: Pharynx
A flame cell is a specialized excretory cell
Flame cells function like a kidney, removing waste materials.
The beating of cilia resembles a flame, giving the cell its name.

21. Nerve Response
Flatworms are able to sense and respond to at least three forms of stimuli:
Sense and respond to light: The eye-spots can detect light and allow the Flatworms to respond to it
Sense and respond to chemicals: Pits on the side of their head regions can sense chemicals in the water and allow the Flatworms to respond (like “smelling”)
Sense and respond to touch: The auricles on either side of the head region can sense touch and allow the Flatworms to respond

22. The ganglia in the head region relay messages from the sensory organs down the nerve cords to the rest of the body. The nerve cords can control muscles in the body which allow the Flatworms to move or eat.

23. Auricles

24. Movement
The flatworms move across a surface using cilia on their ventral surface
They can also move by contracting circular and longitudinal muscles that lay just below the ectoderm. These muscles are controlled by the nerve cords.

25. Reproduction Asexual Reproduction:
Flatworms can asexually reproduce through a process called fission. The anterior and posterior ends hold a surface and the midsection constricts. This results in two new flatworms, one from the anterior end of the original flatworm and the other from the posterior end of the original flatworm.

26. Reproduction
Flatworms can also regenerate parts they have lost.

27. Sexual Reproduction: Flatworms are hermaphroditic
After two flatworms have copulated they release sacs of fertilized eggs and attach them to a surface

28. Parasitic Flatworms: Tapeworms
The tapeworm has an anterior end called a scolex with complicated hooks for attaching to the intestines of its host.
The tapeworm does not have a mouth or digestive system. Instead they bath in the pre-digested fluids of their host and absorb nutrients directly into their body cells

29. Hooks
Scolex
Suckers
Proglottids

30. Lifecycle of a Tapeworm

31. Phylum Platyhelminthes The “flat” “worms”

32. 4 Classes of Phylum Platyhelminthes
TREMATODA – flukes
CESTODA – tapeworms
MONOGENEA – small, parasitic flatworms
TURBELLARIA - small, free-living flatworms

33. Identifying Characteristics of the Phylum Platyhelminthes
Acoelomate
Exhibit bilateral symmetry
Have a bilateral nervous system with cephalization at the head end. Some species exhibit eyespots sensitive to light
Possess a Gastrovascular Cavity (GVC) and primitive organ systems for digestion and excretion
Do not have a circulatory or respiratory system but do take in O2 through their body surface (integumentary exchange)
Hermaphroditic : can reproduce sexually (do not self fertilize) or asexually by regeneration
Are motile and utilize an undulation form of motion
Found in marine, freshwater and damp terrestrial habitats

34. Free-living Flatworms Planaria : Dugesia tigrina
Freshwater, free-living flatworm
Moves by beating cilia and gliding on a film of mucus
3-12mm in size
Have a single opening to their stomachs in the middle of their bodies
Possesses two eyespots (ocelli) that are sensitive to light
Carnivorous (eat daphnia and midges)
Common to most parts of the world
Reproduce by asexual reproduction and capable of regeneration (see next slide)

35. Planaria Regeneration
Planarians will spontaneously detach the tail end of their bodies and each half will regenerate into a full size flatworm
Planarians can be cut either transversally (shown above) or dorsally and most will regenerate into a full size worm
Super Cool Fact: the smallest piece of planarian to ever regenerate in a lab into a new planarian was 1/279th of a planarian! That’s approximately 10,000 cells!

36. Parasitic Flatworms The pork tapeworm – Taenia solium
Infects pigs and humans
Lives in the intestine of its host and passes eggs through the feces
Highly adapted to constant internal environments
Lacks sensory organs, coordination for mobility and a digestive system (more room for reproductive structures!)
Have a modified epidermis “tegument” which protects against the digestive enzymes and the immune systems of the host
Can reach 7m in length in humans!
Are flat and long which maximizes absorption of nutrients from the host

37. The tapeworm “up close and personal….”
The head end has a scolex with four suckers (two seen here) that help it attach to the intestine of its host
The body is separated into sections called “proglottids” that house highly developed reproductive systems (darkened areas) capable of producing hundreds of thousands of eggs and sperm

38. Life cycle of the Pork Tapeworm

39. Super cool Flatworm Fact
the largest tapeworm ever reported was in a sperm whale and was 30 meters in length!
Tapeworm Scolex