Lecture Notes: Animal Diversity

Overview

• Focus on subdivisions of animals based on:
  • Symmetry
  • Body tissue layers
  • Celiums
• Understanding phylogenetic trees is crucial for studying animal diversity.
  • Phylogenetic tree: Timeline showing appearance of organisms & physical characteristics.

Phylogenetic Trees

• Show common ancestors at divergence points.
• More shared ancestors = closer relationship between organisms.
• Example: Mollusks, annelids, and arthropods share common ancestors.

Classification by Symmetry

1. Asymmetry

   • No symmetry (e.g., sponges).
   • Characteristics: Blind ending gut, no true tissues, made of two cell layers, no celium, sessile (do not move).

2. Radial Symmetry

   • Symmetrical around a central axis (e.g., jellyfish, sea anemones).
   • Characteristics: Sense in multiple directions, hydrostatic skeleton, two tissue layers, often aquatic.

3. Bilateral Symmetry

   • Divisible into symmetrical halves on either side of a unique plane (e.g., most animals).
   • Characteristics: Cephalization, three tissue layers, have celium.

Tissue Layers

• Sponges: No true tissues, just cell layers.
• Diploblastic: Two tissue layers (endoderm, ectoderm), e.g., nadarians.
• Triploblastic: Three tissue layers (endoderm, mesoderm, ectoderm), allows for more complex organs and systems.

Celiums

• Acoelomates: No body cavity (e.g., flatworms).
• Pseudocoelomates: Body cavity partially lined with mesoderm (e.g., roundworms).
• Coelomates: Body cavity fully lined with mesoderm (e.g., most complex animals).
  • Advantages: Larger, independent organ development, complex digestion.

Major Animal Groups

1. Peripheria (Sponges)

   • Simplest animals, filter feeders, no true tissues.

2. Nadaria (Jellyfish, Coral, Sea Anemones)

   • Diploblastic, have nematocysts, two body forms (polyp, medusa).

3. Platyhelminthes (Flatworms)

   • Mix of complex and simple traits, cephalization, acoelomates.

4. Annelida (Segmented Worms)

   • Hydrostatic skeleton, cephalization, coelomate.

5. Arthropoda (Insects, Spiders, Crabs)

   • Exoskeleton, most successful organisms, triploblastic.

6. Chordata (Birds, Fish, Mammals)

   • Endoskeleton, spinal cord, advanced cephalization.
     • Characteristics: Four appendages, triploblastic, complex organs.

Study Tips

• Focus on understanding and using terminology correctly.
• Review phylogenetic trees for common ancestors.
• Revisit lecture content for terminology recap.