Dolphins though appear like fish are actually classified under Aquatic Mammals category. By this we mean, they live in water [aquatic] and the females of the species feed the young ones milk through their Mammary glands.
There are several varieties of the Dolphins family including the Ocean Dolphins, the River Dolphins, even the Killer Whale is a Dolphin category and the Dolphin Whale.
Dolphins have slender bodies that are shaped like the fish. They can vary in sizes ranging from five to thirty feet long. Dolphins have a snout, they can swim quite fast and have sharp teeth to help them catch other fast-moving fish. They have a very acute sense of hearing. They make various sounds like clicks, whistles, etc.
Body structure and parts: More specifically the Dolphin body is shaped like a torpedo, conical with a tapering front end, ending in a snout. And a tapering backend ending a bifid tail fin. Dolphins have a small neck but it is not mobile and so the head appears to be attached to the body. The limbs of the Dolphin are modified into flippers that help in swimming, along with the tail fin. Another special characteristic of the Dolphin anatomy is the presence of the blowhole for breathing. There is a hole at the top of its head that connects with the respiratory system of the Dolphin. It is a modified nostril that through evolution has moved on the top of its head, to give easy of breathing while underwater. It blows air out, and sometimes with a waterjet through the blowhole and breathes air in through the same.
Intelligent animals: Many biology researchers consider Dolphins to be the most intelligent animals on the Planet Earth. It is not easy to conduct detailed experiments on Dolphins and other animals, but through the accumulated evidence over time, Dolphins seem to have quite advanced intelligence and creativity characteristics as compared to other animals. Social group behaviours, complex problem solving, creativity, etc. are some of the patterns studied and observed so far. Dolphins move arounds in groups of ten or sometimes even a lot larger, called a pods. Pod behaviours of Dolphins have also been extensively studied.
Dolphins are aquatic mammals and are considered the most intelligent animals on Earth.