Dolphins have a streamlined fusiform body which has been adapted by evolution to swim fast in the ocean. There is a diversity of sizes which range from 1.7 meters up to 8 meters in length, but they have characteristics that differentiate them from porpoises and other cetaceans.
Dolphins are an informal subset of the order Cetacea. Therefore they share some characteristics, but they also have some significant differences.
Most species have gray skin tones ranging from light to dark gray, but most have whitish bellies. There are some other with black, blue, brown colors with stripes, spots or even huge parts of their bodies. Some river dolphins have pinkish skin combined with different shades of gray or white.
The patterns of these colors in their bodies and the lines and stripes in their skins are also assorted.
Most dolphins have a fin at the top of their back which helps them to balance and direct their body and a horizontal caudal fin that moves from top to bottom that creates the movement. However, to add more variety to dolphin anatomy, not all dolphins have this dorsal fin as a couple of species lack of it. Notice that the caudal fin does not move from side to side as can be observed in fish.
Finally, all Dolphins have a pair of flippers that help to give direction to the movement when swimming.