Answer:
Transparency - Creatures such as jellyfish and squid have adapted into a transparent jelly form to stay hidden from predators and prey
“Piezolytes” - Keeps many sea creatures from being crushed by underwater pressure and being turned into biomolecules
Reproduction Patterns w/light - One such example, the angler fish, would use the light attached to it's head to signal a certain light pattern to attract mates and reproduce