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Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
BIOLOGYA GUIDE TO THE NATURAL WORLD
FOURTH EDITION
DAVID KROGH
Animals
Chapter 23
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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)
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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)
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Major Groups of Invertebrates
1. Sponges
2. Cnidarians (jellyfish, sea anemones)
3. Flatworms (tapeworms)
4. Segmented worms (earthworms, leeches)
5. Molluscs (snails, clams, squid)
6. Roundworms
7. Arthropods (spiders, insects, crustaceans)
8. Echinoderms (starfish, sea urchins)
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Comparing Animal Groups
• Animals can be categorized based on three traits:
1. Symmetry
2. Type of gut
3. Body cavity
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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)
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Symmetry
Figure 23.3
Radial symmetry:Symmetry around a central point
Asymmetry:No planes of symmetry
Bilateral symmetry:Symmetry across the sagittal plane
dorsal
posterior
ventral
anterior
sagittalplane
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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)
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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)
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Acoelomate
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Pseudocoel
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Coelom
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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
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Sponges
Figure 23.6
osculum
Inner cells withflagella createcurrents.
The currentscause water toflow into poresand out theosculum at top.
Spiculesstrengthenthe walls.
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Sponges
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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
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Nematocysts
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Cnidarians
Figure 23.8
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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)
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Planarian Organ Systems
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Planaria
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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
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Segmented Worms
Figure 23.13
anus
segments
coelomic space
muscular wallsbetween
segments
pairs of bristles
mouth “hearts”
intestine
brain
dorsalblood vessel
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Annelid Diversity
Figure 23.14
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Molluscs
• Mostly aquatic
• Include a variety of groups:
1. gastropods (snails and slugs)
2. bivalves (oysters, mussels, clams, etc.)
3. cephalopods (squid, octopus, nautilus)
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Mollusc Traits
• Molluscs have 3 defining traits:
1. A mantle drapes over the body and usually produces a shell
2. A fleshy foot is used for movement
3. Most have a rasping mouthpart (or radula) for shredding food
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Molluscs
Figure 23.15
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Roundworms
• Mostly aquatic
• Use their pseudocoel as a hydrostatic skel.
• Parasites or free-living decomposers
• Human parasitic roundworms include:
1. pinworms and hookworms
2. the worm that causes trichinosis (often from undercooked pork)
3. the worm that causes elephantiasis
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Parasitic Roundworms
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Arthropods
• Mostly terrestrial
• Is the largest group of animals (more than 1 million species)
• Have a segmented body and paired jointed 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
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Arthropod Groups
• Three main groups:
1. Uniramians (insects, centipedes, millipedes)
2. Crustaceans (crabs, shrimps, barnacles)
3. Chelicerates (spiders, mites, scorpions)
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Arthropods
Figure 23.18
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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)
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Echinoderms
Figure 23.24
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Sea Star
Figure 23.25
tiny spines andgills on surface
digestive glands
eye spot
mouth(bottom center)
water intakefor tube feet
tubefeet
interior bulbsof tube feet
direction oflocomotion
Tube feet enablesea stars to “walk”and hold on to prey
bulb
anusstomachs