If an animal of euphotic zone has to survive in abyssal zone, what adaptations are required to survive there?

The deepest depth of the ocean is known as the Abyssal zone. The environment is harsh and dark here.
The water is too cold and the organisms here face more pressure than the organisms at the surface.
Organisms to survive here need to have special adaptations to withstand the harsh environment. The Abyssal organisms are small with large flexible stomach and big mouths.
They also show bioluminescence. They live in a dark environment so need light for catching their prey.