Overview of Animal Kingdom Classification

Introduction

• The animal kingdom is vast with about 8.7 million species.
• Classification into phyla (singular: phylum) is based on simple criteria.

Basic Organization of Animals

• All animals are made up of cells which form tissues, organs, and organ systems.
• Primitive animals only have cellular organization without tissues or organs.

Phylum Porifera

• Characteristics: Primitive, cellular organization, no symmetry.
• Example: Sponges with pores in their bodies.

Symmetry in Animals

• Bilateral Symmetry: Body divided into two equal halves by one plane (e.g., humans).
• Radial Symmetry: Multiple planes divide the body into equal halves (e.g., jellyfish, flowers).

Phylum Cnidaria

• Characteristics: Radial symmetry, two tissue layers (diploblastic).
• Examples: Jellyfish.

Phylum Ctenophora

• Characteristics: Similar to Cnidaria, radial symmetry, diploblastic.
• Examples: Comb jellies.

Diploblastic vs Triploblastic

• Diploblastic Animals: Two tissue layers – ectoderm and endoderm.
• Triploblastic Animals: Three tissue layers – ectoderm, mesoderm, and endoderm.

Body Cavities in Animals

• Acoelomates: No body cavity (e.g., Phylum Platyhelminthes – flatworms).
• Pseudocoelomates: False body cavity, fluid-filled (e.g., Phylum Nematoda – roundworms).
• Coelomates: True body cavity located within the mesoderm.

Higher Phyla of Animals

1. Phylum Annelida
   • Examples: Leeches, earthworms.
2. Phylum Arthropoda
   • Characteristics: Largest phylum, includes insects, arachnids, crustaceans.
3. Phylum Mollusca
   • Examples: Snails, oysters, octopuses.
4. Phylum Echinodermata
   • Examples: Starfish.
5. Phylum Hemichordata
   • Examples: Marine worm-like creatures.
6. Phylum Chordata
   • Characteristics: Most evolved phylum with vertebrates.
   • Examples: Mammals, birds, reptiles, fish, humans.

Summary

• Classification is based on body organization, symmetry, tissue layers, and body cavities.
• Progression from primitive cellular level to complex organ systems in chordates.