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Worms and Mollusks

Worms and Mollusks. Chapter 27. Flatworms. Section 27-1. What is a flatworm?. Phylum Platyhelminthes No more than a few millimeters thick Have tissues and internal organ systems Have bilateral symmetry and cephalization

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Worms and Mollusks

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  1. Worms and Mollusks Chapter 27

  2. Flatworms Section 27-1

  3. What is a flatworm? • Phylum Platyhelminthes • No more than a few millimeters thick • Have tissues and internal organ systems • Have bilateral symmetry and cephalization • Known as acoelomates (“without coelem,” which is a fluid filled body cavity)

  4. Form and Function in Flatworms • Feeding • Digestive cavity with a single opening through which both food and wastes pass • Parasitic worms obtain nutrients from foods that have already been digested by their hosts

  5. Form and Function in Flatworms • Respiration, Circulation, and Excretion • Rely on diffusion to: • Transport oxygen and nutrients to internal tissues • Remove carbon dioxide and other wastes from their bodies • Have no gills or respiratory organs, heart, blood vessels, or blood • Some have flame cells – remove excess water and filter wastes from the body

  6. Excretory System

  7. Form and Function in Flatworms • Response • A head encloses several ganglia (groups of nerve cells) that control the nervous system • Have eyespots that look like eyes, but are groups of cells that can detect changes in the amount of light in their environment

  8. Form and Function in Flatworms • Movement • Two means of movement: • Cilia to help glide through water • Muscle cells allow them to twist and turn

  9. Form and Function in Flatworms • Reproduction • Most are hermaphrodites that reproduce sexually • A hermaphrodite is an individual that has both male and female reproductive organs • Asexual reproduction takes place by fission, in which an organism splits in two

  10. Groups of Flatworms • Three main groups of Flatworms • Turbellarians • Flukes • Tapeworms • Most turbellarians are free-living • Most other flatworm species are parasites

  11. Turbellarians • Free-living flatworms • Live in marine or freshwater

  12. Flukes • Class Trematoda • Parasitic flatworms • Infect the internal organs of their host

  13. Tapeworms • Class Cestoda • Long, flat, parasitic worms • Adapted to life inside the intestines of their host • No digestive tract • Absorb already digested nutrients from host

  14. Roundworms Section 2

  15. What is a Roundworm? • Phylum Nematoda • Slender, unsegmented worms with tapering ends • Range in size from microscopic to a meter • Most are free-living, inhabiting soil and water • Others are parasitic

  16. What is a Roundworm? • Have a pseudocoelom (“false coelom”) • Have a digestive tract with two openings – a mouth and an anus

  17. Form and Function in Roundworms • Have specialized tissues and organ systems • Body systems of free-living roundworms are more complex than parasitic ones

  18. Form and Function in Roundworms • Feeding • Predators that use grasping mouthparts to catch and eat small animals • Respiration, Circulation, and Excretion • Exchange gases and excrete metabolic waste through their body walls • Depend on diffusion to carry nutrients and waste through their bodies

  19. Form and Function in Roundworms • Response • Simple nervous systems • Have several types of sense organs • Movement • Muscles extend the length of their bodies • Reproduction • Reproduce sexually, and most have separate sexes

  20. Roundworms and Human Disease • Parasitic roundworms include: • Trichinosis-causing worms • Filarial worms • Ascarid worms • Hookworms

  21. Trichinosis-Causing Worms • Trichinosis – terrible disease caused by the roundworm Trichinella • Adult worms live and mate in the intestines of their hosts • Humans usually get the disease from eating undercooked pork

  22. Filarial Worms • Threadlike worms that live in blood of birds and mammals • Causes elephantiasis

  23. Ascarid Worms • Serious parasite of vertebrate animals • Causes malnutrition in more than 1 billion people worldwide • Absorbs digested food from the host’s small intestine

  24. Hookworms • 25% of people in the world are affected with hookworms • Live in host’s intestines • Feed on blood, causing weakness and poor growth

  25. Annelids Section 27-3

  26. What is an Annelid? • Phylum Annelida • Worms with segmented bodies • Each segment is separated by a septum • Have a true coelom

  27. Form and Function in Annelids • Feeding and Digestion • Many get their food using a pharynx • Food moves from the pharynx, into the esophagus, the crop, the gizzard, and then to the intestine • Others obtain food by filter feeding • Circulation • Closed circulatory system – blood is contained within a network of blood vessels

  28. Form and Function in Annelids • Respiration • Aquatic annelids often breath through gills • Land-dwelling annelids take in oxygen and give off carbon dioxide through their moist skin • Excretion • Digestive wastes pass through the anus at the end of the digestive tract • Cellular waste is eliminated through nephridia (excretory organs)

  29. Form and Function in Annelids Nephridia

  30. Form and Function in Annelids • Response • Well developed nervous system consisting of a brain and several nerve cords Brain Ganglia

  31. Form and Function in Annelids • Movement • Two groups of muscles that work together as part of a hydrostatic skeleton • Reproduction • Most reproduce sexually • Some have separate sexes, others are hermaphrodites

  32. Groups of Annelids • Three classes of Annelids • Oligochaetes • Leeches • Polychaetes

  33. Oligochaetes • Class Oligochaeta • Contains earthworms and their relatives • Streamlined bodies • Relatively few setae • Most live in soil or freshwater

  34. Leeches • Class Hirudinea • External parasites that suck the blood and body fluids of their host

  35. Polychaetes • Class Polychaeta • Contains sandworms, blood worms, and relatives • Marine annelids that have paired, paddlelike appendages tipped with setae (brushlike structures)

  36. Ecology of Annelids • Earthworms and many other annelids spend their lives burrowing through soil, aerating and mixing it • Earthworms help plant matter decompose • Earthworm castings are rich in nitrogen, phosphorus, potassium, micronutrients, and beneficial bacteria

  37. Mollusks Section 4

  38. What is a Mollusk? • Soft-bodied animals • Usually have an internal or external shell • Free-swimming larval stage called a trocophore

  39. Form and Function in Mollusks • True coeloms • Complex, interrelated organ systems

  40. Form and Function in Mollusks Body Plan • Variation on four main parts: • Foot – takes many forms • Mantle – layer of tissue that covers the mollusk’s body • Shell – made by glands in the mantle • Visceral mass – consists of internal organs

  41. Form and Function in Mollusks Feeding • Can be herbivores, carnivores, filter feeders, detritivores, or parasites • Snails and slugs feed using a tongue-shaped structure called a radula

  42. Form and Function in Mollusks Feeding • Clams, oysters, and scallops use gills • Food enters through a siphon – tubelike structure through which water enters and leaves the body Excurrent siphon Incurrent siphon

  43. Form and Function in Mollusks Respiration • Aquatic mollusks breathe using gills inside their mantle cavity • Land snails and slugs respire through the moist surface of their skin Gills

  44. Form and Function in Mollusks Circulation • Some have open circulatory systems – works well for slow-moving mollusks (snails and clams) • Others have closed circulatory systems – works best for fast moving mollusks (octopi and squid) Heart

  45. Form and Function in Mollusks Excretion • Nephridia remove wastes from the blood and release it outside the body Nephridium

  46. Form and Function in Mollusks Response • Two-shelled mollusks have simple nervous systems • Octopi and relatives have the most highly developed nervous systems of all invertebrates • Octopus opening a jar

  47. Form and Function in Mollusks Movement • Move in a variety of ways • Snails secrete mucus and move over surfaces using the foot • Octopi use a form a jet propulsion Reproduction • Reproduce in a variety of ways • Snails and two-shelled mollusks: external fertilization (sexually) • Tentacled mollusks and some snails: internal fertilization (sexually)

  48. Groups of Mollusks • Three major classes: • Gastropods • Bivalves • Cephalopods

  49. Gastropods • Class Gastropoda • Shell-less or single-shelled • Move using muscular foot on ventral side • Includes: pond snails, land slugs, sea butterflies, sea hares, limpets, and nudibranchs

  50. Bivalves • Class Bivalvia • Have two shells held together by one or two powerful muscles • Include: clams, oysters, mussels, and scallops

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