From the article: Mariana Snailfish (found at depths beyond 26,000 feet (~8000m):
> These extremophiles only grow to be around 11 inches long, but despite their small size, they are among the top predators of their realm. They consume tiny crustaceans hidden in seafloor sediment.
Dunno about 'apex', but there are some awesome predators down there for sure! (anglerfish, gulper-eel, etc)
Some whales are very good divers and sharks can live also in deep waters. They use the area to long distance travels also.
Some sharks are even exclusive from deep waters. I remember the first time I had seen one and it was a kind of a shock. Like a seal made of chocolate, eyes like car lights, a black mouth full of tooth and a poisonous sting.
Well, this is the part of the deep sea where animals don't abound :-) There are some really interesting cnidarians here and a few bony fishes that could fill the role.
