Lecture on Animal Diversity
Overview
- Discuss the subdivisions of animal diversity
- Key aspects: Symmetry, tissue layers, celiums
- Reading phylogenetic trees
- Major animal groups
Phylogenetic Trees
- Timeline of organism evolution
- Multi-cellular common ancestors
- Common ancestors found at points of divergence
- Determine relation by counting shared common ancestors
- Example: Mollusks vs. annelids vs. arthropods
Classification by Symmetry
- Asymmetry
- Only found in sponges (Phylum: Peripheria)
- Characteristics: No true tissues, two cell layers, no celium, sessile
- Radial Symmetry
- Found in jellyfish, sea anemones (Phylum: Cnidaria)
- Characteristics: Sense in multiple directions, two tissue layers, hydrostatic skeleton, no celium
- Bilateral Symmetry
- Most animals, complex organisms
- Characteristics: Cephalization, three tissue layers, celium
Tissue Layers
- Diploblasts (e.g., Cnidaria)
- Two tissue layers: Endoderm and ectoderm
- Triploblasts
- Three tissue layers: Endoderm, mesoderm, ectoderm
- Mesoderm allows for specialized organs
Celiums
- Acoelomates: No body cavity, organs within tissues (e.g., flatworms)
- Pseudocoelomates: Unstable cavity, more complex organs (e.g., roundworms)
- Coelomates: True body cavity, independent organs (e.g., most complex animals)
Advantages of Coelom
- Larger, more complex organs
- Independent organ growth and repair
- Diverse diet, adaptability to environments
Major Animal Phyla
- Porifera (Sponges)
- Simplest animals, filter feeders, sessile, two cell layers
- Cnidaria (Jellyfish, Corals, Sea Anemones)
- Diploblastic, stinging cells (nematocysts), two body forms: Medusa & polyp
- Platyhelminthes (Flatworms)
- Simplified systems, cephalization, acoelomate
- Annelida (Segmented Worms)
- Hydrostatic skeleton, need moisture, triploblastic with celium
- Arthropoda (Insects, Spiders, Crabs)
- Exoskeleton, most successful, triploblastic, cephalization
- Chordata (Birds, Fish, Mammals)
- Endoskeleton, spinal cord, advanced cephalization, triploblastic
Summary
- Importance of terminology
- Review and repetition for understanding
Study Tip: Focus on understanding the terminology and the hierarchical structure of animal classification based on symmetry, tissue layers, and celiums.