📖 Short Notes: Animal Classification
1.0 Introduction to Kingdom Animalia
- Nature: Multicellular, Eukaryotic, and Heterotrophic (cannot make their own food).
- The Notochord Factor: The primary division is based on the Notochord (a rod-like support structure).
- 🚫 Non-Chordates: Notochord is absent (Invertebrates).
- ✅ Chordates: Notochord is present (Vertebrates).
2.0 Levels of Organization
| Level | Description | Example |
|---|---|---|
| Cellular | Loose group of cells | Porifera (Sponges) |
| Tissue | Cells form tissues | Coelenterata (Hydra) |
| Organ | Tissues form organs | Platyhelminthes |
| Organ System | Organs work together | Humans, Insects |
3.0 Body Symmetry
Asymmetrical
No equal parts (Sponges)
No equal parts (Sponges)
Radial
Equal halves in many planes (Starfish)
Equal halves in many planes (Starfish)
Bilateral
Left & Right mirror images (Humans)
Left & Right mirror images (Humans)
4.0 Layers & Body Cavity
⭐ Diploblastic: 2 layers (Ecto + Endo).
⭐ Triploblastic: 3 layers (Ecto + Meso + Endo).
Coelom (The Cavity):
• Acoelomate: No cavity (Flatworms).
• Pseudocoelomate: False cavity (Roundworms).
• Coelomate: True cavity lined by mesoderm (Annelids to Chordates).
💡 Evolution Tip: Triploblastic animals are the only ones that can have a true coelom!
5.0 Phylum Porifera (Pore-Bearers)
- 📍 Common Name: Sponges.
- 📍 Body: Asymmetrical; covered with pores called Ostia.
- 📍 Water Flow: Water enters via ostia and exits through a large hole called the Osculum.
- 📍 Mobility: Non-motile (attached to rocks).
- Examples: Sycon, Spongilla, Euspongia.
6.0 Phylum Coelenterata (Hollow-Gut)
- 📍 Common Name: Cnidarians.
- 📍 Body: Diploblastic (2 layers) and Radially Symmetrical.
- 📍 Special Feature: Tentacles with stinging cells (Cnidoblasts) for defense and catching prey.
- 📍 Lifestyle: Can be solitary (Hydra) or colonial (Corals).
- Examples: Jellyfish (Aurelia), Sea Anemone, Hydra.
7.0 The Worm Groups
| Feature | Platyhelminthes | Nematoda | Annelida |
|---|---|---|---|
| Type | Flatworms | Roundworms | Segmented Worms |
| Body Shape | Dorso-ventrally flattened | Cylindrical, tapering ends | Ring-like segments |
| Coelom | Acoelomate (None) | Pseudocoelom (False) | True Coelom |
| Examples | Planaria, Tapeworm | Ascaris, Hookworm | Earthworm, Leech |
💡 Exam Note: Annelids are the first animals to show Metamerism (true internal and external segmentation) and a Closed Circulatory System.
8.0 Phylum Arthropoda (Jointed Legs)
- 📍 Size: The largest phylum in the animal kingdom.
- 📍 Body: Segmented into Head, Thorax, and Abdomen.
- 📍 Exoskeleton: Hard outer covering made of Chitin (shed during growth/molting).
- 📍 Circulation: Open circulatory system (blood fills the body cavity).
- 📍 Special Feature: Jointed appendages (legs/antennae).
- Examples: Cockroach, Butterfly, Spider, Prawn, Crab.
9.0 Phylum Mollusca (Soft-Bodied)
- 📍 Body: Soft, unsegmented, and Triploblastic.
- 📍 Structure: Divided into Anterior Head, Muscular Foot, and Visceral Mass.
- 📍 Protection: Most have a hard Calcareous Shell.
- 📍 Excretion: Have kidney-like organs.
- Examples: Pila (Snail), Octopus, Sepia (Cuttlefish), Pearl Oyster.
10.0 Phylum Echinodermata (Spiny-Skinned)
- 📍 Habitat: Exclusively marine animals.
- 📍 Symmetry: Adults are Radially Symmetrical; Larvae are Bilaterally Symmetrical.
- 📍 Locomotion: Move using a Water Vascular System and Tube Feet.
- 📍 Skeleton: Spiny skin made of calcium carbonate.
- Examples: Starfish (Asterias), Sea Urchin, Sea Cucumber.
Quick Check: Circulation Type
| Arthropoda: Open | Mollusca: Open | Annelida: Closed |