Week 4

• key features of animals

  • multicellular eukaryotes
  • cells without cell walls
  • heterotrophs: ingest food and digest it internally
  • generally mobile, able to respond rapidly to stimuli
  • most reproduce sexually
• evolution of multicellularity through colonial flagellate hypothesis


  infolding of cells into the center of the spherical colonies formed tissue layers
• different animal groups classified by

  • number of tissue layers
  • type of body symmetry
  • presence of body cavity
  • presence of segmentation
  • developmental paths
• simplest animals


  don't have true specialized tissues
• diploblastic animals

  two layers of tissues but no specialized organs
• triploblastic animals

  three embryonic tissue layers
• ectoderm


  skin and nervous system
• endoderm


  digestive tract and derived organs
• mesoderm

  muscles, reproductive system
• tissues

  groups of cells that interact and perform specific functions
• protostomes

  blastopore becomes mouth; mouth develops first
• deuterostomes


  blastopore becomes anus; anus develops first
• asymmetrical body


  no pattern to body plan
• radial symmetry

  • several planes divide into mirror images
  • allows organism to extend in all directions from one central point
• bilateral symmetry


  • only one plane produces mirror image
  • accompanied by cephalization
• cephalization

  the concentration of sensory organs and a brain in a defined head region
• segmentation

  • division of animal body into repeated sections, externally or internally
  • adds flexibility and potential for speciation
  • segments may be fused and modified for special functions
• coelom

  fluid-filled cavity completely within the mesoderm that provides organs with flexibility and absorbs shock
• acoelomate


  no body cavity

  
• pseudocoelomate

  body cavity lined partly by mesoderm and endoderm

  
• coelomate


  completely lined by mesoderm

  
• porifera (sponges)

  • aquatic
  • asymmetrical or radially symmetrical
  • simple animals --> no tissues or organs
  • overall shape usually stiffened by mineral spine
  • adults are sessile (fixed in one place)
  • filter-feeders: depend on water flow, cells digest food intracellularly
• cnidarians (jellies, corals, anemones)

  • aquatic (predominantly marine)
  • radially symmetrical
  • adults have two forms: polyp (sessile with tentacles), medusa (free-swimming)
  • some species go through both as stages
  • two tissue layers enclose a non-cellular jelly substance
  • incomplete digestive tract with tentacles around the mouth
  • predators: stinging cnidocytes help catch prey
  • hydrostatic skeletons (in some)
• annelids (earthworms, leeches)

  • terrestrial and aquatic
  • bilateral symmetry
  • have repeated body segments
  • complete digestive tract; coelom
  • closed circulatory system, simple nervous and excretory system
  • detritivores, bloodsuckers, filter-feeders, predators
  • hydrostatic skeletons
• mollusks (snails, clams, squid)

  • aquatic and terrestrial
  • unsegmented
  • bilaterally symmetrical and asymmetrical
  • hydrostatic skeleton, with supporting external or internal shell secreted by mantle tissue
  • complete digestive tract, coelom
  • muscular foot provides movement
  • filter-feeders, herbivores, and predators
• arthropods (insects, spiders, crabs, prawns)

  • terrestrial, freshwater, marine
  • segmented body plan: major body regions - head, thorax, abdomen; jointed appendages
  • exoskeleton of chitin and protein: must molt to grow
  • open circulatory system, extensive respiratory system of tubes open to the outside
  • complete digestive tract, coelom
  • simple brain, well-developed nerves
• echinodermata (starfish, sea cucumbers, sea urchins)

  • marine
  • five-part radial symmetry with bilaterally symmetrical larvae
  • complete digestive tract
  • water vascular system with tube feet act as gills, sense organs, perform circulatory and excretory functions
  • predators, detritivores
• chordates (lancelets, tunicates, hagfish, and vertebrates)

  • vertebrates share this clade with some invertebrates
  • four distinguishing features of chordates at some point of development: notochord, dorsal + hollow nerve cord, pharyngeal pouches or slits, postanal tail
• cells

  basic building blocks of the body
• tissues

  cells that interact and provide specific functions
• organs

  two or more interacting tissues
• organ systems

  two or more organs joined physically or functionally
• epithelial tissue

  • cover body's internal and external surfaces with one or more layers of tightly packed cells
  • one surface exposed either to the outside or to a space within the body
  • opposite surface anchored to other tissues by a basement membrane
  • functions: protection, nutrient absorption, gas diffusion, secretion
• epithelial tissue layers

  simple, stratified, pseudostratified

  
• epithelial tissue shapes

  squamous, cuboidal, columnar

  
• connective tissue

  • most variable tissue type
  • functions: fill spaces, attach epithelium to other tissues, protect and cushion organs, provide mechanical support
• types of connective tissue

  loose, dense, specialized (blood, cartilage, bone)
• nervous tissue


  transmit information rapidly within an animal's body by electrical and chemical signals
• neurons

  form communication networks that receive, process, and transmit information
• neuroglia


  support cells that assist neurons in functioning