Chapter 19 – Animal Kingdom Essentials

Fundamental Animal Characteristics

  • Heterotrophic: obtain energy by consuming other organisms.
  • Motile at some life stage.
  • Multicellular with specialized cells.

Four Major Evolutionary Distinctions

  • Presence of tissues/organs.
  • Symmetry: asymmetrical, radial, or bilateral.
  • Embryonic gut development:
    • Protostome: mouth first.
    • Deuterostome: anus first.
  • Growth type:
    • Molting (ecdysis) vs. continuous growth.

Symmetry Quick-Check

  • Asymmetry: no plane of equal halves.
  • Radial: pie-like around central axis.
  • Bilateral: mirror-image left & right.

Growth Patterns

  • Molting → periodic shed of exoskeleton (e.g., arthropods, nematodes).
  • Continuous → steady enlargement (e.g., annelids, chordates).

Phyla Accounting for >96\% of Species

  • Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Nematoda, Arthropoda, Echinodermata, Chordata.

Key Phylum Snapshots

Porifera (Sponges)
  • No tissues/organs; filter-feed; sessile adults.
Cnidaria (Jellyfish, Corals)
  • Radial; cnidocytes; polyp vs. medusa forms; coral reefs = calcium carbonate skeletons.
Platyhelminthes (Flatworms)
  • Bilateral; protostome; non-molting; many parasites.
Annelida (Segmented Worms)
  • Bilateral; protostome; segmentation aids movement; non-molting.
Mollusca (Snails, Clams, Octopi)
  • Bilateral; protostome; most with shells; diverse diets (herbivore–predator).
Nematoda (Roundworms)
  • Bilateral; protostome; molt; ubiquitous parasites of plants/animals.
Arthropoda (Insects, Arachnids, Crustaceans, Myriapods)
  • Bilateral; protostome; exoskeleton; molt; unmatched diversity.
    • Insects: 33 pairs legs, thoracic wings, complete metamorphosis.
    • Arachnids: 44 pairs legs, predatory mouthparts.
    • Crustaceans: usually 55 head appendages, aquatic.
    • Centipedes (venomous) vs. Millipedes (detritivores); many leg pairs.
Echinodermata (Starfish, Urchins)
  • Deuterostome; radial adults / bilateral larvae; continuous growth; close invertebrate relatives of chordates.
Chordata
  • Deuterostome; bilateral; continuous growth.
  • Shared embryonic traits: notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail.
  • Subgroups: Tunicates, Lancelets, Vertebrates.

Vertebrate Highlights

  • Notochord replaced by vertebral column.
  • Key innovations:
    • Jaws & paired fins → active predation & maneuverability.
    • Classes: jawless fishes, cartilaginous fishes, ray- & lobe-finned fishes, amphibians, reptiles (incl. birds), mammals.

Water-to-Land Transition (Tetrapods)

  1. Respiration → lungs (from swim bladder).
  2. Gravity → sturdy limbs (from lobe-fins) & reinforced vertebrae.
  3. Egg desiccation → amniotic, waterproof shell.