Biology 320 Invertebrate Zoology Fall 2005 Highlights from Chapter 6 Introduction to Eumetazoa

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

 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 Eumetazoan Tissues

 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

 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

 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

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

 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

Movement Vs. Body Size  Smaller animals  Often move using cilia  Don’t coast after stopping in water  Friction overcomes momentum due to large SA:Vol  Large animals  Typically move using musculature  Continue to move after stopping  Smaller SA:Vol  Surface area is correlated with drag, while volume is correlated with musculature