0 - 200m
The epipelagic zone is home to all sorts of iconic animals, like whales and dolphins, tunas, jellyfishes, sharks, and many other groups. Sunlight can penetrate the surface and there is enough light to see easily down to 200 meters.
200 - 1000m
The mesopelagic zone, or middle open ocean stretches from the bottom of the epipelagic down to the point where sunlight cannot reach. The mesopelagic zone is much larger than the epipelagic, and the most numerous vertebrates on Earth live in this zone.
Many of the species of fishes and invertebrates that live here migrate up into shallower, epipelagic depths to feed, but only under the cover of night.
1000 - 4000m
The next deepest zone is called the bathypelagic zone, or lower open ocean. It is the largest ecosystem on earth. The upper bound of this zone is defined by a complete lack of sunlight.
Organisms in the bathypelagic live in complete darkness, 24 hours per day. The darkness can be interrupted, however, by some light caused by the organisms themselves. This so called bioluminescence can be used to attract prey or to find a mate. Some species have lost their ability to see anything at all.
4000 - 6000m
Deeper still is the abyssopelagic zone, which stretches from the bottom of the bathypelagic to the seafloor, which is at around 6000 meters deep on average. This zone is characterized by a relative lack of life. The pressure is incredibly high, it truly is the abyss.
6000 - 11000m
A special zone that only exists in certain places around the world is called the hadopelagic zone. Where deep, wide trenches occur in the otherwise flat seafloor, the open water that fills them is the hadopelagic zone. By this definition, all of the deepest parts of the ocean conclude in the hadopelagic. The deepest known ocean depth is nearly 11000 meters.