Here are the major classes of vertebrates:
* Fish: This class includes a wide variety of aquatic animals, including bony fish, cartilaginous fish (like sharks and rays), and jawless fish (like lampreys and hagfish).
* Amphibians: This class includes frogs, toads, salamanders, and newts. They are known for their ability to live in both water and on land.
* Reptiles: This class includes snakes, lizards, turtles, crocodiles, and alligators. They are characterized by their scaly skin and eggs with tough, leathery shells.
* Birds: This class includes all feathered animals. They are warm-blooded, lay eggs, and have wings (although some birds, like penguins, have lost the ability to fly).
* Mammals: This class includes animals that have fur or hair, give birth to live young, and nurse their offspring with milk.
All vertebrates share these key characteristics:
* Backbone (vertebral column): This is the defining feature of vertebrates, a series of bones that protect the spinal cord.
* Internal skeleton: Vertebrates have an internal skeleton made of bone or cartilage, which provides support and allows for movement.
* Closed circulatory system: Vertebrates have a heart and a network of blood vessels that carry blood throughout the body.
* Brain and central nervous system: Vertebrates have a well-developed brain and a central nervous system, which controls their body's functions.
* Bilateral symmetry: Vertebrates have a body plan that is symmetrical along a central axis.
So, when someone talks about "vertebrate animals", they're referring to all the animals that belong to the subphylum Vertebrata, encompassing a huge variety of creatures with fascinating adaptations and evolutionary history.