All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal (vertebral column and/or notochord), with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below. Like all chordates, vertebrates are animals with four defining traits, at least during the embryonic stage: notochord, dorsal hollow nerve cord, post-anal tail, and pharyngeal slits. Invertebrate chordates retain some or all of these traits, including the notochord, throughout life. Vertebrates, in contrast, develop a vertebral column, or... Show more

All vertebrates are built along the basic chordate body plan: a stiff rod running through the length of the animal (vertebral column and/or notochord), with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below.

Like all chordates, vertebrates are animals with four defining traits, at least during the embryonic stage: notochord, dorsal hollow nerve cord, post-anal tail, and pharyngeal slits. Invertebrate chordates retain some or all of these traits, including the notochord, throughout life. Vertebrates, in contrast, develop a vertebral column, or backbone, from the notochord after the embryonic stage.    
The vertebral column runs from head to tail along the dorsal (top) side of the body. It is made up of repeating units of bone called vertebrae (singular, vertebra). The vertebral column helps the vertebrate body hold its shape. It also protects the spinal nerve cord that runs through it. The vertebral column is the core of the vertebrate endoskeleton, or internal skeleton. In addition to the vertebral column, the vertebrate endoskeleton includes a cranium, or bony skull, that encloses and protects the brain; two pairs of limbs; and two limb girdles that connect the limbs to the rest of the endoskeleton.    
Besides the vertebral column and the rest of the endoskeleton, most vertebrates share several other traits.

The majority of vertebrates have:    
- scales, feathers, fur, or hair covering their skin;    
- muscles attached to the endoskeleton to allow movement;    
- a circulatory system with a heart that pumps blood through a closed network of blood vessels;    
- an excretory system that includes a pair of kidneys for filtering wastes out of the blood;    
- a central nervous system with a brain and spinal cord, as well as nerve fibers that run throughout the body;    
- an adaptive immune system that learns to recognize specific pathogens and launch tailor-made attacks against them;    
- an endocrine system with glands that secrete chemical messenger molecules called hormones.

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