Lecture Notes: Animal Diversity

Overview

• Key Topics: Structure and classification of animals based on symmetry, body tissue layers, and celiums.
• Main Skill: Reading and interpreting a phylogenetic tree.

Phylogenetic Tree

• Definition: A timeline showing how organisms evolved.
• Function: Illustrates common ancestors and points of divergence.
• Use: Determine relationships by counting shared ancestors; more shared ancestors indicate closer relations.

Animal Classification Criteria

Symmetry

• Asymmetry: No symmetry, represented by sponges.
• Radial Symmetry: Symmetrical all around central axis, e.g., jellyfish.
• Bilateral Symmetry: Mirror-image halves, common in most animals.

Tissue Layers

• Diploblastic: Two layers (ectoderm and endoderm), seen in cnidarians.
• Triploblastic: Three layers (ectoderm, mesoderm, endoderm), allows more complex structures.

Celomic Structures

• Acoelomates: No body cavity, e.g., flatworms.
• Pseudocoelomates: False cavity, some separation of organs, e.g., roundworms.
• Coelomates: True cavity with complex organ systems, e.g., humans.

Major Animal Phyla

1. Porifera (Sponges)

• Characteristics: Simplest animals, filter feeders, two cell layers.
• Habitat: Aquatic environments.

2. Cnidaria (Jellyfish, Corals, Anemones)

• Characteristics: Diploblastic, radial symmetry, nematocysts (stinging cells).
• Forms: Polyp (stationary) and medusa (mobile).

3. Platyhelminthes (Flatworms)

• Characteristics: Simple gut, some cephalization, acoelomate.
• Habitat: Aquatic and parasitic.

4. Annelida (Segmented Worms)

• Characteristics: Hydrostatic skeleton, need moisture, triploblastic.
• Examples: Earthworms, leeches.

5. Arthropoda (Insects, Spiders, Crabs)

• Characteristics: Exoskeleton, diverse habitats, triploblastic.
• Success: Most successful due to adaptability and water retention.

6. Chordata (Birds, Fish, Mammals)

• Characteristics: Endoskeleton, spinal cord, advanced cephalization.
• Defining Traits: Segmentation, four appendages, true coelom.

Conclusion

• Emphasis on Terminology: Understanding and recalling specific terms is crucial.
• Overall Goal: Use these classifications and characteristics to understand animal diversity and evolutionary relationships.