Biology 320 Invertebrate Zoology Fall 2005

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Biology 320Invertebrate ZoologyFall 2005

• Highlights from Chapter 6
• Introduction to Eumetazoa

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What Defines an Animal?

• Irritability responds to external stimuli
• Locomotion
• Sense of direction
• Polarized distribution of organs
• Sponges are classified as Parazoa (near
  animals) by some, and animals by others
• Clearly metazoan
• Have unified distribution of cells

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Eumetazoan Tissues

• All eumetazoans posses the four PRIMARY tissue
  types, to some extent
• Epithelium
• Connective tissue
• Muscle tissue
• Nervous tissue
• Epithelia that are more developed and diverse
  than in parazoans
• Has allowed organisms to colonize habitats that
  are more physiologically challenging (i.e.
  freshwater and terrestrial)
• Increases compartmentalization in organisms
• Two main types (generally speaking)
• Epidermis barrier to external environment
  which allows for homeostasis of internal
  environment
• Gastrodermis lines mouth and gut, and allows
  for extracellular digestion

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• Posses connective tissues
• Bind other tissues together
• Offer structural support - skeleton
• Types of skeletons
• Exoskeleton example insect cuticle
• Endoskeleton example sea urchin test
• Hydrostatic skeleton animal has a water-filled
  cavity (i.e. gastrovascular cavity, coelom,
  etc.). Muscle contractions displace water,
  generating force that can be used to do work

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• Eumetozoans posses musculature that allows them
  to bend / turn while moving
• Muscle types
• Smooth
• Cross-striated
• Obliquely striated
• Muscles are usually arranged in antagonistic sets
• One muscle moves body part one way, while the
  other restores its original position
• Human example biceps and triceps
• Tubular invertebrates longitudinal and circular

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• Eumetozoans posses nervous systems
• Neurons evolved with muscle tissue
• Regulate muscle contraction so that animals can
  respond to stimuli
• Nerve impulses travel along membranes of axons
  to effectors (target cells)
• Important terms
• Motor unit
• Synapse
• Neurotransmitter
• Action potential

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Sense Organs

• Animals must respond to stimuli in order to
  survive
• Three main classes of stimuli
• Electromagnetic energy mainly light
• Mechanical energy sound vibrations, touch,
  pressure, gravity
• Chemical stimuli taste, smell
• Animals must posses the appropriate receptors to
  respond to these stimuli
• Photoreceptors
• Mechanoreceptors
• Chemoreceptors

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• Basic reflex arc
• Receptor
• Afferent signal
• Integration center (ganglion, CNS, etc.)
• Efferent signal
• Effector (target cell, organ, etc.)
• Many types of receptors throughout the animal
  kingdom some are very simple and not considered
  to be organs
• Ocelli simple eyes that serve as photoreceptors
• Statocysts gravity / orientation receptors

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Movement Vs. Body Size

• Smaller animals
• Often move using cilia
• Dont coast after stopping in water
• Friction overcomes momentum due to large SAVol
• Large animals
• Typically move using musculature
• Continue to move after stopping
• Smaller SAVol
• Surface area is correlated with drag, while
  volume is correlated with musculature