Study of Flatworms: Phylum Platyhelminthes and Phylum Nematoda

1. Biology 11 – Kingdom AnimaliaStudy of the Primitive Worms Phylum Platyhelminthes: Flatworms Phylum Nematoda: Roundworms Phylum Platyhelminthes

2. The Flukes The Planarians The Tapeworms Phylum Platyhelminthes – the Flatworms

3. Importance of the Flatworms to Evolution • Bilateral body plan – left side mirror image of right • Cephalization – development of the head • sense organs and nerves concentrated in head region • Centralization of nervous system: • Nerve cord accompanies cephalization and bilateral symmetry. • Advanced muscle tissue present; • Primitiveexcretory system • allows removal of metabolic wastes

5. Flatworms (Phylum Platyhelminthes) • Definition: Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization Flatworms are acoelomates, meaning “without a coelom”  coelom = a fluid-filled body cavity that is lined with mesoderm  mesoderm = middle germ layer that gives rise to muscles, circulatory, reproductive, and excretory systems

6. Phylum Platyhelminthes Characteristics • Bilateral symmetry; anterior and posterior ends. • Body flattened • Well-developed epidermis • No internal body cavity other than digestive tube (acoelomate) • Parenchyma (connective tissue) fills space between organs. • Incomplete digestive system • Still one opening • This critter eats and poops out of its mouth – mmmm, pass the popcorn

7. Cross Section of a Flatworm

8. 3mm 3mm 3mm Volume = 3 x 3 x 3 = 27mm2 Area = 6(3 x 3) = 54mm3 3mm 1mm 9mm Volume = 9 x 3 x 1 = 27mm2 Area = 2(9 x 1) + 2(3 x 1) + 2(3x9) = 78mm3 Advantage of Being Flat • Surface area to volume ratio is important for organisms. • Many substances enter and leave through body surface. • Faster absorption and release of wastes

9. Nutrition and Digestion • Typical digestive system includes a mouth, a pharynx, and an intestine. • Parasitic Tapeworms and Flukes lack a digestive system • Parasitic flatworms, such as the Tapeworm absorb molecules from host. • Free living flatworms (Planarians) are carnivorous; suck prey into pharynx with mouth. • Undigested food goes out mouth. Yes, folks, they eat and excrete out the same hole 

10. Flatworm Respiratory, Circulatory, and Excretory System • Lack circulatory, respiratory, and excretory systems. • Flatworms rely on diffusion to transport oxygen and nutrients throughout the body, to remove CO2 and other wastes • Some flatworms have flame cells – specialized cells that remove excess water and metabolic wastes

11. Nervous System and Sense Organs • Have a nerve-net. • Most have more complex system. • Cerebral ganglion = primitive brain coordinates impulses. • “Ladder” system carries impulses throughout body • Many sense organs present • Eyespots • Chemoreceptors, touch sensors and rheoreceptors (sense direction) also common

12. Note: Free-living vs. Parasitic • Free-living (eg Planarians) have well developed digestive and nervous systems to seek-out and process food • Parasitic Tapeworms – rely on host’s digestive system to process food, which absorb. No need for advancement of nervous system – not needed.

15. Reproduction – in Free-living Flatwormssuch as Planarians • May reproduce sexually or asexually • Asexual: • Binary fission – split in two • Sexual: • Both sexes present in same flatworm (hermaphrodites). • Fertilization internal, eggs produced • Embryos emerge as juveniles resembling adults.

16. Reproduction in theTapeworm! • Lack digestive system • Sucker and hooks on anterior end for attachment • Neck produces new segments • Called proglottids • Each proglottid contains male and female gonads • Reproductive output high • Many proglottids per worm • Many eggs per proglottid

17. Groups of Flatworms • Turbellarians Free-living, e.g. planarian • Flukes (Trematoda) Parasites • Tapeworms (Cestoda) Parasites

20. Tapeworm - Life Cycle

21. Flukes -- Life Cycle of a Liver Fluke

22. The Coelom or Body Cavity Advances

23. Another Look at the Coelom

24. Phylum Nematoda (Roundworms) • Definition: • Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings – a mouth and an anus • Pseudocoelom = “false coelom” • Is a body cavity between the endoderm and mesoderm tissues, partially lined with mesoderm tissue

26. Form and Function in Roundworms • Feeding: free-living carnivores; or eat algae, fungi, decaying organic matter • Respiration: gases diffuse through body walls • Circulation: no internal transport system  diffusion • Excretion: metabolic wastes diffuse through body walls

27. Form and Function in Roundworms • Response: ganglia from the head and run through length of body; sense organs to detect chemicals of other organisms • Movement: muscles and fluid of the pseudocoelom function as a hydrostatic skeleton; allows movement (swimming or pushing through soil) • Reproduction: sexual reproduction; internal fertilization, were male deposits sperm inside the female’s reproductive tract

28. Roundworm Ecological Roles • Omnivores that catch and eat algae, fungi, decaying matter • Recyclers • Parasites of Plants – eg. The Golden Nematode attacks potato crops, causing severe devastation • Parasites of animals

29. Ascaris – Parasitic Roundworm of Pigs and Humans

30. Unfortunately, they can Grow quite Big!

32. Parasites: Your Pet's EnemiesTiny parasites that pose a gigantic threat

33. Adult roundworms live in the dog's small intestine.What they do:Cause diarrhea, vomiting, stunted growth, rough coat, bloated belly.How they spread:Almost all puppies get roundworms from their mothers. Dogs can also pick up roundworms from the soil.Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

34. Enlarged hook worm mouth showing 'teeth'.What they do:Attach to the dog's intestinal lining, leaving bleeding internal wounds. Cause blood loss, anemia, and diarrhea. As few as 100 hook worms can kill a puppy.How they spread:Eggs pass through the feces of an infected dog into the soil where they are easily swallowed or can penetrate through a dog's feet.Defending against them: Once a month prevention is recommended, contact your local veterinarian for advice.

35. Symptoms: Larvae digested enter bloodstream and burrow into organs, causing absolutely horrendous pain and in some cases death.

36. Filarial (threadlike worms) are nematodes that may block the passage of Fluids in the Body • Disease: Elephantitis • The disease is caused by parasitic worms, including Wuchereria bancrofti, Brugia malayi, and B. timori, all transmitted by mosquitoes. Lymphatic filariasis currently affects 120 million people worldwide, and 40 million • Blocks Lymphatic nodes which drain fluid to and from the blood. • Tropics, Africa and Asia

37. Phylum Annelida (Earthworms) • Annelida  annellus, meaning “little ring” • Definition: • Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm.

39. Body Plan • The body of an annelid is divided into segments separated by septa (singular: septum) • Septum – internal walls between each segment • Most segments contain the same organs (eyes, antennae, sense), while others are specialized • Most segments have bristles called setae

41. Feeding and Digestion • Annelids may be filter feeders or predators (carnivorous) • Annelids use their pharynx (with jaws) to bring food into the esophagus. The food then go into the crop (food storage) and then to the gizzard (food is ground up). Then food is absorbed in the intestine.

43. Circulation • Annelids have a closed circulatory system. • Closed circulatory system: • Blood is contained in a network of blood vessels • Blood circulates through a dorsal vessel and a ventral vessel, and smaller blood vessels through each segment • Dorsal vessel helps pump blood

45. Respiration • Annelids can respire through: • Gills (worms that live in water) • Diffusion through skin (earthworms)

46. Excretion • Digestive waste passes out anus • Metabolic waste is filtered out by nephridia

47. Response • Most annelids have a well-developed nervous system with a brain and nerve cords • Other sense organs: • Sense receptors, chemical receptors, sensors that detect gravity

48. Movement • Hydrostatic skeleton • Contraction of longitudinal and circular muscles • Annelids can burrow, use setae, or parapodia (paddlelike appendages for swimming or crawling)

49. Reproduction • Sexual reproduction • May have separate sexes and external fertilization OR • Annelids are hermaphrodites and exchange sperm with another worm • Two worms attach, exchange sperm, and store it in sacs • A clitellum (a thick band) secretes a mucus ring where the egg and sperm are released and fertilization takes place inside this ring • The ring falls off the worm and forms a cocoon, where the eggs will hatch

50. Ewwwwwwwwwwwwwwwwwwwwwwwww! Ah, but they are sooooooo in love, don’t you think?