Detailed Summary
The Animal Kingdom is an extensive classification system designed to organize the vast diversity of animal life. Current estimates indicate there are over a million known species, necessitating a structured approach to classification. The classification is founded on fundamental features common across different animals, focusing on several key aspects:
Levels of Organisation
Animals are multicellular but exhibit various organizational patterns. For instance, sponges have a cellular level organization where cells act independently. More complex animals, like coelenterates, display tissue level organization where cells group into tissues, while higher phyla like Annelids and Chordates exhibit organ-system level organization where organs work in functional systems.
Symmetry
Animals can also be categorized based on their body symmetry. Some are asymmetrical, like sponges, while others display radial symmetry (e.g., coelenterates) or bilateral symmetry (e.g., arthropods and chordates).
Diploblastic and Triploblastic Organisation
Animals are divided into diploblastic (two embryonic layers) and triploblastic (three embryonic layers) organizations, affecting their developmental processes and complexity.
Coelom
An important feature in classification is the presence or absence of a body cavity, termed coelom. Animals can be classified as coelomates, pseudocoelomates, and acoelomates based on this criterion.
Segmentation and Notochord
Some animals exhibit segmentation in their bodies, while chordates are characterized by having a notochord, which influences their classification.
Classification of Animals
The section concludes with a detailed overview of various phyla, including Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, and Chordata, elaborating on their key characteristics, examples, and significance in the animal kingdom. Classification aids in understanding evolutionary relationships and biological diversity.