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Animals

Chapter 23. Animals. What is an Animal?. Animals are eukaryotic, multicelled heterotrophs that do not have a cell wall pass through a blastula stage (a hollow, fluid-filled ball of cells that forms once an egg is fertilized by sperm). Groups of Animals.

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Animals

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  1. Chapter 23 Animals

  2. What is an Animal? • Animals are eukaryotic, multicelledheterotrophs that do not have a cell wall • pass through a blastula stage (a hollow, fluid-filled ball of cells that forms once an egg is fertilized by sperm)

  3. Groups of Animals • The animals most familiar to us are vertebrates (have a backbone) • But most of the ~2 million known species of animals are invertebrates(without backbones)

  4. Major Groups of Invertebrates • Sponges • Cnidarians (jellyfish, sea anemones) • Flatworms (tapeworms) • Segmented worms (earthworms, leeches) • Molluscs (snails, clams, squid) • Roundworms • Arthropods (spiders, insects, crustaceans) • Echinoderms (starfish, sea urchins)

  5. Comparing Animal Groups • Animals can be categorized based on three traits: • Symmetry • Type of gut • Body cavity

  6. Symmetry • can the body be cut into mirror images? • Asymmetry– the animal cannot be divided into mirror images (sponges) • Radial symm. – more than one way to produce mirror images (cnidarians) • Bilateral symm. – can form mirror images only one way - into right and left halves (all others)

  7. Symmetry Radial symmetry:Symmetry around a central point Asymmetry:No planes of symmetry Bilateral symmetry:Symmetry across the sagittal plane dorsal sagittalplane posterior anterior ventral Figure 23.3

  8. Type of Gut (= Digestive System) • Region where food is digested and then absorbed • Sponges lack a dig. syst. • Cnidarians and flatworms have a sac-like gut (or incomplete digestive system) has only one opening that serves for both taking in food and expelling waste • All others have tube-like gut (or complete dig. syst.) has an opening at both ends (mouth and anus)

  9. Body Cavities • Bilat. sym. animals may have an open space (or cavity) between the gut and the outer body wall • Flatworms lack this cavity (are acoelomate) • Roundworms have a cavity that lacks a membrane lining (a pseudocoel) • All other bilat. sym. animals have a cavity lined with a membrane (a coelom)

  10. Acoelomate

  11. Pseudocoel

  12. Coelom

  13. Sponges • Are all aquatic • Have a very simple body plan – are little more than a tube of cells that filter food particles out of water • Water is drawn through the body of the sponge and expelled out through a central opening

  14. Sponges osculum Inner cells withflagella createcurrents. The currentscause water to flow into poresand out theosculum at top. Spiculesstrengthenthe walls. Figure 23.6

  15. Sponges

  16. Cnidarians • All are aquatic • Jellyfishes, corals, and sea anemones • Their incomp. dig. syst. is called a gastrovascular cavity (GVC) • They use it as a hydrostatic skeleton (a cavity filled with a pressurized fluid) to support themselves • Have tentacles covered with nematocysts, stinging structures that provide defense and catch prey

  17. Nematocysts

  18. Cnidarians Figure 23.8

  19. Flatworms • Mostly aquatic • Free-living planarians, parasitic tapeworms and flukes • Simplest animals with organ systems • Have a GVC • Are often hermaphrodites (have both male and female reproductive organs)

  20. Planarian Organ Systems

  21. Planaria

  22. Segmented Worms • Show segmentation – the division of the body into many repeating units • Mostly aquatic • Includes earthworms and leeches • Fluid in the coelom acts as a hydrostatic skeleton

  23. Segmented Worms dorsalblood vessel intestine brain “hearts” mouth coelomic space muscular wallsbetweensegments anus pairs of bristles segments Figure 23.13

  24. Annelid Diversity Figure 23.14

  25. Molluscs • Mostly aquatic • Include a variety of groups: • gastropods (snails and slugs) • bivalves (oysters, mussels, clams, etc.) • cephalopods (squid, octopus, nautilus)

  26. Mollusc Traits • Molluscs have 3 defining traits: • A mantle drapes over the body and usually produces a shell • A fleshy foot is used for movement • Most have a rasping mouthpart (or radula) for shredding food

  27. Molluscs Figure 23.15

  28. Roundworms • Mostly aquatic • Use their pseudocoel as a hydrostatic skel. • Parasites or free-living decomposers • Human parasitic roundworms include: • pinworms and hookworms • the worm that causes trichinosis (often from undercooked pork) • the worm that causes elephantiasis

  29. Parasitic Roundworms

  30. Arthropods • Mostly terrestrial • Is the largest group of animals (more than 1 million species) • Have a segmented body and pairedjointed appendages for efficient movement on land • Have a hard but flexible exoskeleton that provides support and limits water loss • It must be shed (or molted) for the animal to grow

  31. Arthropod Groups • Three main groups: • Uniramians (insects, centipedes, millipedes) • Crustaceans (crabs, shrimps, barnacles) • Chelicerates (spiders, mites, scorpions)

  32. Arthropods Figure 23.18

  33. Echinoderms • All aquatic • Sea stars, sea urchins, sea cucumbers, etc. • Larvae start off with bilateral sym. but adults have radial sym. • Have an endoskeleton (internal skel.) with spines or plates of calcium carbonate • Have a water-vascular system with tube feet (is a hydraulic system used for movement, feeding, and gas exchange)

  34. Echinoderms Figure 23.24

  35. Sea Star tiny spines andgills on surface stomachs anus direction oflocomotion bulb digestive glands water intakefor tube feet mouth(bottom center) Tube feet enablesea stars to “walk”and hold on to prey interior bulbsof tube feet eye spot tubefeet Figure 23.25

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