Animal Kingdom Notes

Introduction

The Animal Kingdom, also known as Kingdom Animalia, is one of the most diverse and complex groups in the biological classification system. This kingdom includes a vast array of organisms from simple sponges to complex mammals. Understanding the Animal Kingdom is crucial for NEET aspirants as it forms a significant part of the Zoology syllabus. This study note will break down the key concepts, classifications, and characteristics of the Animal Kingdom to make the topic digestible and easy to understand.

Classification of Animal Kingdom

Basis of Classification

The classification of animals is based on several criteria, including:

1. Levels of Organization: Cellular, Tissue, Organ, and Organ System levels.
2. Symmetry: Radial and Bilateral symmetry.
3. Germ Layers: Diploblastic and Triploblastic.
4. Body Cavity: Acoelomate, Pseudocoelomate, and Coelomate.
5. Segmentation: Presence or absence of segmented bodies.
6. Notochord: Presence or absence of a notochord.

Levels of Organization

1. Cellular Level: Organisms like sponges (Phylum Porifera) have a cellular level of organization where cells are loosely aggregated and do not form tissues.
2. Tissue Level: Organisms like cnidarians (Phylum Cnidaria) have cells organized into tissues.
3. Organ Level: In organisms like flatworms (Phylum Platyhelminthes), tissues are organized into organs.
4. Organ System Level: Higher animals like annelids, arthropods, molluscs, echinoderms, and chordates have organ systems.

Symmetry

1. Radial Symmetry: Body parts are arranged around a central axis. Examples include cnidarians and echinoderms (in their adult form).
2. Bilateral Symmetry: Body has left and right halves that are mirror images. Most animals, including humans, exhibit bilateral symmetry.

Germ Layers

1. Diploblastic: Organisms have two germ layers - ectoderm and endoderm. Example: Cnidarians.
2. Triploblastic: Organisms have three germ layers - ectoderm, mesoderm, and endoderm. Example: All higher animals.

Body Cavity

1. Acoelomate: No body cavity. Example: Flatworms.
2. Pseudocoelomate: Body cavity not entirely lined by mesoderm. Example: Nematodes.
3. Coelomate: Body cavity completely lined by mesoderm. Example: Annelids, Molluscs, Arthropods, Echinoderms, Chordates.

Segmentation

Segmentation is the division of the body into repetitive segments. Example: Earthworms (Phylum Annelida).

Notochord

The notochord is a flexible rod-like structure that provides support. It is present in all chordates at some stage of their life cycle.

Major Phyla of Animal Kingdom

Phylum Porifera

• Common Name: Sponges
• Characteristics:
  • Simplest multicellular animals.
  • Cellular level of organization.
  • Pores all over the body (ostia) for water flow.
  • Skeleton made of spicules or spongin.
  • Example: Sycon, Spongilla, Euspongia.

Phylum Cnidaria

• Common Name: Coelenterates
• Characteristics:
  • Tissue level of organization.
  • Radial symmetry.
  • Diploblastic.
  • Stinging cells (cnidocytes) for defense and capturing prey.
  • Example: Hydra, Jellyfish, Sea Anemone, Coral.

Phylum Platyhelminthes

• Common Name: Flatworms
• Characteristics:
  • Organ level of organization.
  • Bilateral symmetry.
  • Triploblastic.
  • Acoelomate.
  • Example: Planaria, Liver fluke, Tapeworm.

Phylum Nematoda

• Common Name: Roundworms
• Characteristics:
  • Organ system level of organization.
  • Bilateral symmetry.
  • Triploblastic.
  • Pseudocoelomate.
  • Example: Ascaris, Wuchereria (Filarial worm).

Phylum Annelida

• Common Name: Segmented worms
• Characteristics:
  • Organ system level of organization.
  • Bilateral symmetry.
  • Triploblastic.
  • Coelomate.
  • Segmented body.
  • Example: Earthworm, Leech.

Phylum Arthropoda

• Common Name: Arthropods
• Characteristics:
  • Largest phylum in Animal Kingdom.
  • Organ system level of organization.
  • Bilateral symmetry.
  • Triploblastic.
  • Coelomate.
  • Segmented body with jointed appendages.
  • Exoskeleton made of chitin.
  • Example: Prawn, Cockroach, Butterfly, Spider.

Phylum Mollusca

• Common Name: Molluscs
• Characteristics:
  • Organ system level of organization.
  • Bilateral symmetry.
  • Triploblastic.
  • Coelomate.
  • Soft body with a hard shell.
  • Example: Snail, Octopus, Oyster.

Phylum Echinodermata

• Common Name: Echinoderms
• Characteristics:
  • Organ system level of organization.
  • Radial symmetry in adults.
  • Bilateral symmetry in larvae.
  • Triploblastic.
  • Coelomate.
  • Water vascular system.
  • Example: Starfish, Sea urchin, Sea cucumber.

Phylum Chordata

• Common Name: Chordates
• Characteristics:
  • Organ system level of organization.
  • Bilateral symmetry.
  • Triploblastic.
  • Coelomate.
  • Notochord present at some stage.
  • Dorsal hollow nerve cord.
  • Pharyngeal slits.
  • Post-anal tail.
  • Subphyla: Urochordata, Cephalochordata, Vertebrata.
  • Example: Humans, Fish, Birds, Amphibians, Reptiles, Mammals.

Conclusion

The Animal Kingdom is a vast and diverse group that includes numerous phyla, each with unique characteristics. Understanding the basis of classification and the key features of each phylum is essential for mastering this topic in NEET Zoology. Use this study note as a guide to break down complex concepts into digestible parts and enhance your preparation.