The deepest part of the Ocean is the Mariana Trench which has been recently explored in 2016. At the bottom of the ocean the ecosystem is very different from any other part of the world, aquatic or not, as species need to thrive in an environment with little to no light and a high amount of water pressure at all times. As such, many lifeforms have specializes photocells that generate light to draw in prey or scare away predators.
Along with animals, there are entire coral reefs at the bottom of the ocean with rare coral and flower like creatures and plants that all have evolved and adapted to life in the dark. Along with this, there are even grape sizes amoebas that are attached to the sandy bottom and coral that can be seen without the need for a microscope.