Animal Classification: Kingdom to Phylum

• Animal classification involves categorizing animals based on evolutionary relationships, anatomy, physiology, genetics, and behavior.
• The purpose is to develop a hierarchical system reflecting the evolutionary history of the animal kingdom.

Kingdom Classification

• The broadest classification is the Kingdom, with animals in Kingdom Animalia.
• Animals are multicellular, eukaryotic, heterotrophic (obtaining nutrients by consuming other organisms), and lack cell walls.
• Animals generally reproduce sexually and undergo embryonic development.

Phylum Characteristics

• Within Kingdom Animalia, organisms are classified into phyla based on fundamental body plan characteristics.
• Examples of phyla:
  • Porifera (sponges): lack true tissues, have porous bodies.
  • Cnidaria (jellyfish, corals): radial symmetry, stinging cells (cnidocytes).
  • Platyhelminthes (flatworms): bilateral symmetry, acoelomate (lacking a body cavity).
  • Nematoda (roundworms): pseudocoelomate (false body cavity), cylindrical body.
  • Annelida (segmented worms): coelomate (true body cavity), segmented body.
  • Mollusca (snails, clams, squids): soft body, often with a shell.
  • Arthropoda (insects, spiders, crustaceans): exoskeleton, segmented body, jointed appendages.
  • Echinodermata (starfish, sea urchins): radial symmetry (adults), water vascular system.
  • Chordata (vertebrates, tunicates, lancelets): notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail.
• Each phylum shows a unique set of anatomical and developmental features.

Class Distinctions

• Within each phylum, organisms are further classified into classes based on specific characteristics.
• Examples within Phylum Chordata:
  • Class Agnatha (jawless fish): lack jaws, cartilaginous skeleton.
  • Class Chondrichthyes (cartilaginous fish): cartilaginous skeleton, possess jaws.
  • Class Osteichthyes (bony fish): bony skeleton, possess jaws.
  • Class Amphibia (frogs, salamanders): undergo metamorphosis, typically require water for reproduction.
  • Class Reptilia (reptiles): amniotic eggs, scales.
  • Class Aves (birds): feathers, wings, lay hard-shelled eggs.
  • Class Mammalia (mammals): hair or fur, mammary glands, give birth to live young (mostly).
• Classes are defined by shared characteristics like skeletal structure, reproductive strategies, and physiological adaptations.

Family and Genus Relationships

• Each class is divided into orders, families, genera, and species.
• Family: Groups of closely related genera sharing common characteristics.
• Genus: A group of closely related species sharing a recent common ancestor.
• Species: A group of organisms that can interbreed and produce fertile offspring.
• The binomial nomenclature system assigns each species a two-part name: the genus name followed by the species name (e.g., Homo sapiens).
• This hierarchical system reflects the evolutionary relationships among different groups of animals.