Worms and Mollusks

1. Worms and Mollusks

2. Phylum:Platyhelminthes (flat) (worm) • Simplest bilateral symmetric animals showing a head and tail region. • 3 layers: endoderm, ectoderm, mesoderm • Known as acoelomates (without a coelom) • coelom : a fluid-filled body cavity

3. General body structure:

4. Feeding • Free-living flatworms can eat: • Tiny aquatic animals • Dead animals • Single opening to function as a mouth and anus. • Possess a pharynx which isused to eat

5. Respiration, circulation, excretion • Breath through diffusion • Flame cells: specialized cells used for removing excess water.

6. Planarians (c. Turbellaria) • Free-living freshwater flatworm. • Possess a digestive tract, mouth, pharynx, and branched intestine. • Feed on small microscopic animals • No skeletal,circulatory,or respiratory system

8. Planarians continued • Small brain with two nerve cords • Hermaphrodites • Internal fertilization • Can also reproduce asexually.

9. Marine Flatworms polycadia Strange mating behavior Beautiful colors

10. Parasitic flukes (c. Trematoda) • Usually two or more hosts. • Primary host: human (site of asexual reproduction) • Causes the disease schistosomiasis

11. Removal of a Liver Fluke…warning graphic

12. Tapeworms (c. Cestoda) • Parasites. Example: beef tapeworm • Head region (scolex) : contains suckers and hooks used to attach to a host organism. • Proglottids : square body segments used for reproduction

15. Phylum: Nematoda (roundworms) • Long cylindrical bodies • Often covered with a thick cuticle • 1 mm to 1 meter in length • Both free-living and parasitic • *** 2 body openings*** • Major difference from the flatworms • Food and wastes will NOT be mixed

16. Form and function • Eat small animals, bacteria, algae, fungi, etc • Exchange gases through diffusion • Possess a simple nervous system • Move through contracting muscles • Reproduce sexually

17. Trichina worm • Causes trichinosis • Often present in pigs. Grow to about one millimeter in length and become cysts in pig muscles. • People eat contaminated pork and larval cysts develop into adults in human intestines. • New larvae can end up in human muscles.

19. Ways to prevent trichinosis: • Thoroughly cook pork products • Feed hogs uncontaminated feed • Freeze pork immediately after packaging

20. Filaria • Roundworm that causes the disease elephantiasis. • Carried by mosquitoes • Infects bloodstream and blocks lymph nodes resulting in severe swelling.

21. Ascarid worms • Affects more than 1 billion people • Affect people, horses, pigs, chicken, cattle, dogs, cats etc.

22. Pinworms and Hookworms • PINWORMS • Most common nematode infection in N. America • Especially infants and toddlers.

23. HOOKWORMS • Often will enter through the feet. • Common in areas where sewage disposal is inadequate

25. Phylum: Annelida • Also known as the segmented worms. • The body is divided into separate body segments. • Marine,fresh water,and on land. • Parasitic and free-living. ex.

26. Annelida Characteristics • Characteristics of Annelida:-1)Bilaterally symmetrical. • 2)Body has more than two cell layers, tissues and organs. • 3)Body cavity is a true coelom. • 4)Body possesses a through gut with mouth and anus. • 5)Body has 3 separate sections, a prosomium, a trunk and a pygidium. • 6)Has a nervous system with an anterior nerve ring, ganglia and a ventral nerve chord. • 7)Has a true closed circulatory system. • 8)Has no true respiratory organs.

27. …more annelid facts • “tube within a tube” body plan. • Closed circulatory system, 2 openings

28. respiration • Aquatic annelids breathe using gills • Land-dwelling annelids breathe through the skin

29. excretion • Nephridia : excretory organs that filter nitrogenous waste in the ceolom.

30. Reproduction • Hermaphroditic. eggs and sperm released at the clitellum

31. Marine Annelids Class Polychaeta-means many bristles

32. Earthworms • C. Oligochaeta • First segment = prostomium • Setae = small hair-like extensions on ventral surface used for locomotion. • Possess many “hearts”

33. The “hearts” of an earthworm:

34. Leeches-Class Hirundinea • Mainly freshwater. • Suckers on both ends of body • Saliva of leeches contain enzymes that prevent blood from clotting (anticoagulants)

35. Attaches to prey with posterior sucker, and uses anterior sucker to “suck” blood. Leech Anatomy

37. Medicinal uses of leeches • Used to be used for “leeching” by early physicians to rid a sick person of “bad” blood. • Still used in surgery to prevent blood clotting and unwanted swelling due to excess blood.

38. Phylum: Mollusca • Second largest phyla of animals after the arthropods. • Found in fresh water, salt water, and on land • ex.

39. Mollusk characteristics: • Soft bodies, 3 cell tissue layers • Many are used for food and jewelry • Possess a foot = large ventral muscle used for movement. • Most have a radula (exception: bivalves) • Mantle - fold of skin that surrounds the body organs

40. 1. bivalves • 2 parts to their shells (bi). • Strong adductor muscles to keep the shell closed • Incurrent siphon – carries water and food into the mantle cavity • Excurrent siphon – siphon where water is expelled.

41. Examples of bivalves: scallops clams and mussels oysters

42. pearls • Mother-of-pearl inner smooth part of bivlave shell. • Made primarily by oysters when a foreign object gets lodged inside between mantle and shell. • Come in many colors

43. Reproduction and nutrition • Bivalves are filter-feeders. (plankton and small invertebrates) • Separate sexes • Sperm is released by the excurrent siphon and enters a female via the incurrent siphon where fertilization takes place.

44. Video of bivalve dissection

45. 2. gastropods • Largest class of mollusks • Most possess a single shell.exception: slug slugs conch snails

46. 3. cephalopods • Most advanced mollusks • All are marine predators • Use tentacles to gather and manipulate food • Can swim rapidly by expelling a jet of water from their mantle cavity. • Some may discharge an inky fluid for defense • Octopus (8 arms) squid (10 tentacles)

47. examples: nautilus cuttlefish octopus squid