The aquatic environment differs from the conditions of the ground-air environment in that water is many times denser in structure than air. For this reason, animals that are in the water all the time have streamlined body contours, and are also better adapted to the increased pressure of water on their bodies. In the water, in contrast to the surface of the land, there are no negative temperatures, and its differences between day and night are not so strong and sharp. The amount of light in the water is much less than on the surface, so the animals also had to adapt to this.
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