The Core Distinction: The Backbone
The fundamental difference between vertebrates and invertebrates lies in the presence or absence of a vertebral column, more commonly known as a backbone or spine. Vertebrates are animals that possess a backbone, while invertebrates are animals that do not.
Section 2: Characteristics of Vertebrates
Vertebrates are characterized by an internal skeleton (endoskeleton) made of bone or cartilage, with a central backbone that protects the spinal cord. This group includes mammals, birds, reptiles, amphibians, and fish. They generally have more complex body structures and well-developed organ systems.
Section 3: Characteristics of Invertebrates
Invertebrates make up over 95% of all animal species and lack an internal backbone. To provide support and protection, many invertebrates have an external skeleton called an exoskeleton (like insects and crabs), while others have fluid-filled cavities that act as a hydrostatic skeleton (like jellyfish and worms), or no skeleton at all.
Section 4: Examples in the Animal Kingdom
This classification is the first major division within the animal kingdom. Examples of vertebrates include humans, lions, eagles, snakes, and sharks. Common invertebrates include spiders, butterflies, squids, starfish, and sponges. Understanding this difference is the first step in animal taxonomy.