Chapter 23 - Animals: The Invertebrates
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Characteristics of animals
- multi-cellular, diploid
- heterotrophs, either consuming other organsims or absorbing nutrients
from them
- require oxygen
- most reproduce sexually
- most are motile in at least part of their life cycle
- life cycle includes stages of embryonic development
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Major groups of animal diversity
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32 phyla exist
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2 major groups of phyla
- invertebrates
- vertebrates
- animals grouped and classified based on several characteristics
- level of body organization (cellular, tissue, organ)
- type of symmetry (none, radial, bilateral) [Figure 23.3]
- cephalization (concentration of sensory organs in a head)
- type of gut (none, sac-like, tubular)
- type of body cavity (none, false, true) [Figure 23.4]
- segmentation (repeating body units)
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Invertebrate phyla
- Sponges
- cells, but no tissues or organs
- no symmetry, cephalization, gut, or body cavity
- filter feeders [Figure 23.7]
- many have skeletons
- Cnidarians
- tissues, but no organ systems
- radial symmetry
- sac-like gut
- alternation of body forms
- have nematocysts
- Flatworms
- simple nervous system
- sac-like gut
- no body cavity
- are hermaphrodites
- Roundworms
- beginning of cephalization
- complete tubular digestive system
- false body cavity
- are cylindrical and tapered at both ends
- are notorious parasites
- Mollusks
- fleshy, soft body but most have a shell
- respiratory organs of gills or lungs
- have a radula (rasping) organ for feeding
- some have well developed eyes
- Segmented worms (annelids)
- complex organ system
- body segmented into repeating units
- most have bristles on each side of their body
- Arthropods
- segmented body, segments grouped into functional units
- hardened exoskeleton of chitin
- jointed appendages
- respiratory structures
- specialized sensory structures
- very diverse
- Echinoderms
- have a water vascular system
- metamorphosis of a bilateral larva to a radial adult
- skin is spiny
© Carol L. Wymer, 2003