Lecture Notes: Animal Diversity

Overview

• Focus: Understanding subdivisions of animals
  • Symmetry
  • Body tissue layers
  • Celiums (body cavities)
• Importance of reading phylogenetic trees

Phylogenetic Trees

• A timeline showing how organisms appear and evolve
• Common ancestors represented at divergence points
• The closer the common ancestors, the closer the animals are related
• Example: Mollusks vs. Annelids vs. Arthropods
  • Count shared common ancestors to determine relatedness

Classification by Symmetry

• Asymmetry

  • Example: Sponges (Porifera)
  • No true tissues, no celium, blind-ending gut
  • Sessile, simple filter feeders

• Radial Symmetry

  • Example: Cnidaria (jellyfish, sea anemones)
  • Senses in multiple directions
  • Two tissue layers, hydrostatic skeleton
  • No celium, blind-ending gut

• Bilateral Symmetry

  • Most animals
  • Cephalization: development of a head with sensory organs
  • Three tissue layers, presence of celium

Tissue Layers

• Diploblasts

  • Two tissue layers: endoderm and ectoderm
  • Example: Cnidaria

• Triploblasts

  • Three tissue layers: endoderm, mesoderm, and ectoderm
  • Mesoderm allows for complex organ development

Celiums (Body Cavities)

• Acoelomates

  • Example: Flatworms
  • Solid tissue layers, organs embedded within

• Pseudocoelomates

  • Example: Roundworms
  • Simple body cavity, organs not well-fixed

• Coelomates

  • Example: Most animals
  • True body cavity with complex, independent organs

Animal Phyla

Porifera (Sponges)

• Aquatic, filter feeders
• Simplest animals, unchanged for long periods
• Two cell layers, not tissue layers

Cnidaria

• Examples: Jellyfish, corals, sea anemones
• Diploblastic, stinging cells (nematocytes)
• Two body forms: polyp (juvenile) and medusa (adult)

Platyhelminthes (Flatworms)

• Free-living or parasitic (e.g., tapeworms)
• Acoelomates, cephalization
• Simple nervous system

Annelida (Segmented Worms)

• Examples: Earthworms, leeches
• Triploblastic, true celium
• Cephalization, hydrostatic skeleton

Arthropoda

• Examples: Insects, spiders, crabs
• Exoskeleton, molt yearly
• Triploblastic, cephalization
• Most successful phylum, adaptable

Chordata

• Examples: Birds, fish, mammals
• Endoskeleton (bone or cartilage)
• Spinal cord along dorsal side
• Cephalization, segmentation
• Four appendages, triploblastic

Study Tips

• Familiarize with phylogenetic trees and terminology
• Understand how classification relates to physical traits and evolutionary history
• Review specific screenshots and revise terminology frequently

Conclusion: Mastering animal diversity involves understanding the classification systems and evolutionary relationships, as well as the specialized terminology used to describe these concepts.