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Flatworms Phylum: PLATYHELMINTHES

Flatworms Phylum: PLATYHELMINTHES. VS. Class Turbellaria includes: Planarians. Class Cestoda Includes: Tapeworms. Class Trematoda Includes: Flukes. II. Body Plan/Structure. Flatworms demonstrate a bilaterally symmetrical body plan

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Flatworms Phylum: PLATYHELMINTHES

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  1. FlatwormsPhylum: PLATYHELMINTHES

  2. VS.

  3. Class Turbellariaincludes: Planarians

  4. Class CestodaIncludes: Tapeworms

  5. Class TrematodaIncludes: Flukes

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

  7. 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)

  8. 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

  9. Flatworms do have true organsand 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 tissuecalled ganglia (singular=ganglion) that resembles a primitive brain.

  10. Cephalization

  11. They have two nerve cordsthat 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

  12. Auricles

  13. 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

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

  15. Respiration • Respiration occurs by diffusion

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

  17. 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.

  18. 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

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

  20. Auricles

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

  22. 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.

  23. Reproduction • Flatworms can also regenerate parts they have lost.

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

  25. 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

  26. Hooks Scolex Suckers Proglottids

  27. Lifecycle of a Tapeworm

  28. Phylum PlatyhelminthesThe “flat” “worms” www.onacd.ca

  29. 4 Classes of Phylum Platyhelminthes TREMATODA – flukes CESTODA – tapeworms MONOGENEA – small, parasitic flatworms TURBELLARIA - small, free-living flatworms

  30. 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

  31. Free-living FlatwormsPlanaria : 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)

  32. 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!

  33. Parasitic FlatwormsThe 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

  34. 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

  35. Life cycle of the Pork Tapeworm

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

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