Diversity of Life

The Eukaryotes III: Animals

Characteristics of animals

  1. Multicellular eukaryotes
  2. Nutrition: ingestive heterotrophs
  3. Sexual reproduction (most)
  4. Complex embryonic development

Phylogeny of animals: developmental trends

Body symmetry
  1. Earliest animals have radial symmetry
    1. Sponges
    2. Jellyfish & sea anemones
  2. Bilateral symmetry results in specialization of head (cephalization)
  3. Pentaradial symmetry: an exception in the trend
  1. Earliest animals have no true tissues
  2. Development of true tissues: endoderm and ectoderm
  3. Development of middle tissue: mesoderm
Fluid-filled body cavity (coelom)
  1. Primitive animals have no cavity
  2. "False" coelom forms between mesoderm and endoderm
  3. True coelom forms within mesoderm
Development of digestive tract
  1. Primitive animals have only a cavity
  2. One-way digestive tract first arose in roundworms
  3. Protostomates: animals whose digestive tract forms "mouth first"
  4. Deuterostomates: animals whose digestive tract forms "mouth second"

Animal Diversity

  1. Porifera: The Sponges
    1. Epidermal cells, feeding cells (choanocytes), transport cells (amoebocytes)
    2. Spicules (skeleton fibers) for support; may be hard or soft
  2. Cnidarians: jellyfish et al.
    1. Hollow gastrovascular cavity for eating, circulation
    2. Most have 2 life stages: polyp and medusa
    3. Feeding tentacles have stinging cells (cnidocytes)
    4. Examples: Jellyfish, coral, sea anemone
  3. Platyhelminthes: The Flatworms
    1. Bilateral, with gastrovascular cavity
    2. Flat; may be 1 mm - 20 m in length
    3. Examples: Fluke, Tapeworm, Planaria
  4. Nematodes: The Roundworms
    1. Very diverse: > 90,000 species
    2. One-way digestive tract, false coelom
    3. Most are free-living, some are parasitic
    4. Examples: Pinworm, Trichinella
  5. Mollusca: Snails etc.
    1. 150,000 + species known, mostly marine
    2. Coelom, one-way GI tract, specialized organs
    3. Soft bodies; hard shell in most
    4. Bodies have 3 main parts: foot, visceral mass, mantle
    5. Open circulatory system in most
    6. Examples: snails, slugs, clams, oysters, squid, octopus
  6. Annelids: Segmented worms
    1. Segmentation and closed circulation
    2. Examples: Earthworm, polychaetes, leeches
  7. Arthropods
    1. > 1 million species known; most wide-spread and numerous animals
    2. Body plan segmented, with jointed appendages
    3. Exoskeleton (chitin) - requires molting
    4. Head, thorax, abdomen, 6 - 8 legs, antennae (most)
      1. Arachnids: spiders, ticks, mites, scorpions
      2. Crustaceans: crabs, lobster, shrimp, barnacle, pill bugs
      3. Millipedes and centipedes
      4. Insects: moth, bee, grasshopper
        • adapted to flight: 1 or 2 pairs of wings
        • 3 pairs of walking legs
        • Metamorphosis in many includes larvae (maggots, grubs, caterpillars)
        • Insects are important as pollinators, pests, in food chains, as disease vectors
  8. Echinoderms
    1. "Spiny-skinned", pentaradial
    2. Water vascular system for circulation and feeding (tube feet)
    3. Exampls: sea stars, sea cucumbers, sea urchins
  9. Chordates
    1. 4 characteristics: pharyngeal gill slits, post-anal tail, notochord, dorsal nerve cord
    2. Invertebrates: lancelets and tunicates (sea squirts)
    3. Vertebrates: fish, birds, mammals, amphibians, reptiles

Vertebrate diversity

  1. Class Agnatha: jawless fish
  2. Class Chondrichthyes: cartilagenous fish
  3. Class Ostheichthyes: bony fish
    1. Ray-finned fish: salmon, seahorse
    2. Lobe-finned fish: coelocanth
    3. Lungfish
  4. Class Amphibia: toads, frogs, salamanders
  5. Class Reptilia: turtles, snakes, crocodiles, alligators, chameleon, dinosaurs
  6. Class Aves: owls, eagles, emu
  7. Class Mammalia: mammals
    1. Monotremes: platypus
    2. Marsupials: kangaroo
    3. Eutherians: mouse