Characteristics common to all vertebrates include bilateral symmetry, two pairs of jointed appendages, outer covering of protective cellular skin, metamerism, developed coeloms and internal skeletons, developed brains, vertebrae and sensory organs. Vertebrates also have respiratory systems, closed circulatory systems, genital and excretory systems and digestive tracts.
The 12 features that define vertebrates look different in various species but perform the same basic functions. All vertebrates have bilateral lines of symmetry, although some vertebrates look more symmetrical than others. Vertebrates have two pairs of appendages that facilitate locomotion, although these organs appear as fins in some vertebrates but as forelimbs and hind limbs in others.
Vertebrates have outer protective coverings of cellular skin, which appears as scales in some creatures and as hair and feathers in others. Vertebrates have coeloms, or body cavities, that are lined entirely with epithelium, or cellular tissue. This tissue is then divided into two or four distinct compartments.
These organisms also have structured internal skeletons made of cartilage and bone, which are separated into an axial skeleton and appendicular skeleton. All vertebrates have brains enclosed by skulls and nerve cords surrounded by strong vertebrae, which protect these vulnerable organs from damage. Lastly, vertebrates have genital and excretory systems and digestive tracts with livers and pancreases.