The sea consists of thousands of species of interesting creatures who dwell in the waters with the support of their largely significant gills and fins. Many of these species are unknown, living in either the surface zone, the sunlit zone, the twilight zone, and the midnight zone (four zones making up a sea or ocean).
All the creatures living in the sea have certain peculiarities that are of much use, for any of the zones that they are adapted to.
The Abyss, the darkest and coldest of them all, utterly black and freezing, holds very little species due to its location, and the trenches, deep depressions located at the very bottom of the ocean floor, hold hardly anything at all, for nearly all the creatures in the ocean are unable to cope with this dark, cold habitat.
Many creatures of the midnight zone have a successful and helpful advantage with the hunting of prey, which is a light that attracts fishes passing by, who approach the light and come close enough to be eaten by the predator. Viper-fish are a species known to have this large advantage.