Worms and Mollusks

1. Worms and Mollusks Chapter 27

2. Worms Unsegmented Worms Flatworms (Platyhelminthes) Turbellarians, Trematoda (Flukes), Cestoda(Tape Worms) Round Worms (Nematodes) Trichinella, Filarial Worms, Ascaris, Hookworms Segmented Worms Annelids Oligochaetes (Earthworms), Leeches, Polychaetes

3. Unsegmented Worms • The unsegmented worms include: • flatworms and roundworms • The simplest of these is the flatworm

4. FlatwormPhylum Plantyhelminthes • Plantyhelminthes consists of the flatworms • Soft, flattened worms that have tissues and internal organ systems. • They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization • Flatworms are known as acoelomates (A-see-lo-mates) • Without a coelom (see-lem) which is a fluid-filled body cavity that is lined with a mesoderm

8. Form and Function in Flatworms • Feeding • Free living worms are carnivores that feed on tiny aquatic animals • They can be scavengers that feed on dead animals • They have a gastrovascular cavity with a single opening • Near the mouth is a muscular tube called a pharynx

9. Form and Function in Flatworms • Feeding cont. • Parasitic worms feed on the blood tissue fluids, or pieces of cells within a hosts body • These worms do not need a digestive system because their host does the digesting for them • Tapeworms have no digestive system at all

10. Form and Function in Flatworms • Respiration, Cirucluation, and Excretion • Carried out through diffusion (because the worm is so thin) • Flame cells • Specialized cells that filter and remove excess water, urea, and ammonia from the body

11. Form and Function in Flatworms • Response • More developed than that of sponges • Have several ganglia (groups of nerve cells) • Not complex enough to be called a brain • Eyespot • A group of cells that can detect changes in the amount of light in their environment

14. Form and Function in Flatworms • Movement • Typically move in 2 ways • Cilia - Located on their epidermal cells help them to glide through the water and over the bottom of a stream or pond • Muscle Cells - Controlled by the nervous system and allows the worm to twist and turn so that they are able to react rapidly to the environmental stimuli.

15. Form and Function in Flatworms • Reproduction • Most free living flatworms are hermaphroditic • Has both male and female reproductive organs • Sexual reproduction • Two worms join and deliver sperm to one another • The eggs are laid in clusters and hatch within a few weeks

16. Form and Function in Flatworms Reproduction • Asexual reproduction which is common among free living flatworms • Will reproduce by fission • An organism will split into two • Parasitic flatworms • Often have complex life cycles that involve both sexual and asexual reproduction

17. Groups of Flatworms

18. Groups of Flatworms • The Three Main Groups Include: • Class Turbellarians • Class Trematoda (Flukes) • Class Cestoda (Tapeworms)

19. Groups of FlatwormsClass: Turbellarians • Free living Flatworms • Most live in freshwater or marine environments • Bottom dwellers living in sand or mud • Most are carnivores or detritus • Example: Planarians

23. Groups of FlatwormsClass: Trematoda (Flukes) • Parasitic Flatworms • Most flukes infect the internal organs of their host • Some are external parasites that live on the skin, mouth, gills of their host • Many have complicated life cycles that involve two or more animal hosts

24. Groups of FlatwormsClass: Trematoda (Flukes) • They are usually less than a centimeter long • They cause serious pain to millions of humans and animals • The most destructive live in the tropics.

25. Liver Fluke

26. Groups of FlatwormsClass: Trematoda (Flukes) • Flukes of the genus Schistosoma infect about 200 million people per year • The Schistosoma fluke causes schistosomiasis in humans • A serious disease in which the eggs clog blood vessesel which can cause swelling and tissue decay in the lungs, liver, spleen, or intestines

28. Groups of FlatwormsLife Cycle of Schistosoma • Larvae enter humans through skin • Reproduce sexually in blood vessels of intestines • Release eggs into water • Larvae enter snails and reproduce asexually • Burrow out and infect humans again • More prevalent with no sewage treatment

30. Groups of FlatwormsClass: Cestoda (tapeworms) • Parasitic worms • Adapted to live inside the intestines of their hosts • Food is digested directly through the body walls • They rarely cause death but instead cause weakness and weight loss

31. Tapeworm

32. Structure of a Tapeworm

33. Groups of FlatwormsClass: Cestoda (tapeworms) • Structure of a tapeworm • Scolex • Structure that contains suckers or hooks

34. Groups of FlatwormsClass: Cestoda (tapeworms) • Proglottids • Segments that make up most of the worms body • Proglottids contain male and female reproductive parts • They can contain as many as 100,000 eggs. • They can produce as many as half a billion eggs in a year

35. Proglottids

36. Tapeworm • Taenia saginata, the Beef Tapeworm

37. Roundworms

38. Roundworm Phylum Neamtoda • Nematoda consists of the roundworms • Slender, unsesgmented worms with tapering ends • Range in size from microscopic to a meter in length • A rotting apple may contain 100,000 nematodes

39. Roundworm Phylum Neamtoda • Most species are free-living • Inhabit the soil, salt flats, aquatic sediments and water from polar regions to the tropics • Develop from three germ layers • Have a pseudocoelom (false coelom) • Body cavity between the endoderm and the mesoderm

40. Roundworm Phylum NeamtodaFeeding They are carnivores • They have a digestive tract with 2 openings • Food moves in one direction • Anus • The posterior opening of the digestive tract

41. Respiration, Circulation, and Excretion in Roundworms • Exchange gases and excrete waste through body walls • They rely on diffusion to carry nutrients and waste throughout their bodies

42. Response in Roundworms • Simple nervous systems consisting of several ganglia • Can detect chemicals given off by prey

43. Movement in Roundworms • Muscles extend the length of the body • Together, the muscles and the fluid in the pseudocoelom1 function as a hydrostatic skeleton2. • 1 A fluid-filled space which separates the bodywall from internal organs • 2High internal pressure maintained within the pseudocoelom, pushing outward on the cuticle, can give the nematode a significant structural integrity

44. Reproduction in Roundworms • Roundworms produce sexually through internal fertilization • Most species have a male and a female • Parasitic roundworm, such as hookworms, often have complex life cycles that can involve 2 or 3 different hosts.

45. Roundworms and Human Disease • Parasitic roundworms cause severe pain and suffering in humans. • Examples include: • Trichinosis-causing worms • Filarial worms • Ascarid worms • Hookworms

46. Roundworms Causing Human Disease:Trichinosis-Causing Worms • Trichinosis is a terrible disease caused by the roundworm Trichinella • Adult worms live and mate in the intestines of their hosts which include: • Humans, pigs, and other animals

47. Remember what Felipe always says….Make sure your meat is cooked thoroughly

48. Roundworms Causing Human Disease: Filarial Worms • Found primarily in tropical regions of Asia • Threadlike worms that live in blood and lymph vessels of birds and mammals…including humans!! • Transmitted through bitting insects especially those darn mosquitos

49. Roundworms Causing Human Disease: Filarial Worms • Large numbers of filarial worms may block the passage of fluids within the lymph vessels • This causes what is known as elephantiasis