Study Notes on Animal Characteristics and Classification

Characteristics of Animals

• Heterotrophic, multicellular eukaryotes

• Lack cell walls

• Use oxygen for aerobic respiration

• Primarily sexual reproduction

• Specialized nervous and muscle tissue

Classification of Animals

• Body Symmetry:

  • Bilateral Symmetry: Identical left and right sides

  • Radial Symmetry: Symmetrical around a midline

  • Asymmetry: No symmetry

• Body Cavity Types:

  • Coelom: Fluid-filled cavity with organs

  • Types:

    • Acoelomates: Flattened bodies

    • Coelomates: Complex organ development

Major Animal Groups

• Invertebrates:

  • Phyla Porifera: Simple body plan, sessile, hermaphroditic (e.g., sponges)

  • Phyla Cnidaria: Radial symmetry, stinging cells (e.g., jellyfish)

• Deuterostomes:

  • Echinodermata: Radial symmetry, spiny endoskeleton (e.g., sea stars)

  • Chordata: Backbone or notochord, includes most vertebrates

    • Key Features: Bony skeleton, paired appendages, amniotic eggs

    • Taxonomic Classes: Agnatha (jawless), Chondrichthyes (cartilaginous), Osteichthyes (bony), Amphibia, Reptilia, Aves, Mammalia

Major Animal Groups

• Invertebrates:

  • Phyla Porifera:

  • Simple body plan

  • Sessile (immobile)

  • Hermaphroditic (e.g., sponges)

  • Phyla Cnidaria:

  • Radial symmetry

  • Stinging cells (e.g., jellyfish)

• Deuterostomes:

  • Echinodermata:

  • Radial symmetry

  • Spiny endoskeleton (e.g., sea stars)

  • Chordata:

  • Includes most vertebrates

  • Key Features:

    • Backbone or notochord

    • Bony skeleton

    • Paired appendages

    • Amniotic eggs (in many members)

  • Taxonomic Classes:

    • Agnatha (jawless fish)

    • Chondrichthyes (cartilaginous fish)

    • Osteichthyes (bony fish)

    • Amphibia

    • Reptilia

    • Aves (birds)

    • Mammalia

Taxonomic Classes of Chordata:

• Agnatha:

  • What they are: Jawless fish

  • Key Features: Lack jaws and paired fins, cartilaginous skeleton, notochord persists throughout life.

  • Examples: Lampreys, hagfish

• Chondrichthyes:

  • What they are: Cartilaginous fish

  • Key Features: Cartilaginous skeleton, placoid scales, jaws and paired fins present, internal fertilization.

  • Examples: Sharks, rays, skates

• Osteichthyes:

  • What they are: Bony fish

  • Key Features: Bony skeleton, scales (e.g., cycloid, ctenoid), jaws and paired fins present, usually have a swim bladder or lungs.

  • Examples: Salmon, tuna, seahorses

• Amphibia:

  • What they are: Amphibians

  • Key Features: Typically undergo metamorphosis (aquatic larvae, terrestrial adults), moist skin for respiration, lay eggs in water.

  • Examples: Frogs, salamanders, newts

• Reptilia:

  • What they are: Reptiles

  • Key Features: Ectothermic (cold-blooded), dry scaly skin, lay amniotic eggs on land, lungs for respiration.

  • Examples: Snakes, lizards, turtles, crocodiles

• Aves:

  • What they are: Birds

  • Key Features: Endothermic (warm-blooded), feathers, wings, hollow bones, lay hard-shelled amniotic eggs, beaks without teeth.

  • Examples: Eagles, pigeons, penguins

• Mammalia:

  • What they are: Mammals

  • Key Features: Endothermic, mammary glands (produce milk), hair or fur, diaphragm, viviparous (live birth).

  • Examples: Humans, bats, whales, kangaroos