2.6 Kingdom Classification: Animalia

Characteristics of Kingdom Animalia

• Multicellular: Composed of many cells.
• Eukaryotic: Possess a true nucleus and membrane-bound organelles.
• Heterotrophic: Obtain nutrients by ingesting other organisms.
• No Cell Wall: Animal cells lack a cell wall.
• Motility: Most animals are capable of locomotion.
• Reproduction: Primarily sexual.

(a) Vertebrates

• Definition: Animals that possess a backbone or spinal column.
• Key Characteristics:
  • Presence of a vertebral column.
  • Well-developed internal skeleton.
  • Complex nervous system with a brain enclosed in a cranium.
  • Bilateral symmetry.
  • Closed circulatory system.
• Examples: Fish, Amphibians, Reptiles, Birds, Mammals.

(b) Invertebrates

• Definition: Animals that do not possess a backbone or spinal column.
• Constitute the vast majority of animal species.

Major Invertebrate Phyla (1/2)

1. Porifera (Sponges): Simplest multicellular, sessile, porous body, filter feeders (e.g., Sycon).
2. Cnidaria (Coelenterata): Radial symmetry, stinging cells (cnidocytes), sac-like body (e.g., Jellyfish, Hydra).
3. Platyhelminthes (Flatworms): Dorsoventrally flattened, bilateral symmetry, acoelomate (e.g., Tapeworms, Planaria).
4. Nematoda (Roundworms): Cylindrical, unsegmented, pseudocoelomate, many parasitic (e.g., Ascaris).
5. Annelida (Segmented Worms): Segmented body, true coelom, well-developed organ systems (e.g., Earthworms, Leeches).

Major Invertebrate Phyla (2/2)

6. Arthropoda: Jointed legs, chitinous exoskeleton, segmented body; most diverse (e.g., Insects, Spiders, Crabs).
7. Mollusca: Soft body, usually shelled, muscular foot, mantle (e.g., Snails, Octopuses).
8. Echinodermata: Spiny skin, radial symmetry (adults), water vascular system (e.g., Starfish, Sea Urchins).