He was likely hallucinating if he wasn’t making it up for fun but the coolest and scariest marine cryptid claim is definitely the giant freezing cold carnivorous flesh blob allegedly encountered by a diver in 1953, who said he watched it eat a shark:
“ Suddenly the water became distinctly colder. While the temperature continued to drop with surprising rapidity, I saw a black mass rising from the darkness of the chasm. It floated upwards very slowly. As at last light reached it I could see that it was of dull brown colour and tremendous size, a flat ragged edged thing about one acre in extent. It pulsated sluggishly and I knew that it was alive despite its lack of visible limbs or eyes. Still pulsating, this frightful vision floated past my level, by which time the coldness had become most intense. The shark now hung completely motionless, paralyzed either by cold or fear. While I watched fascinated, the enormous brown thing reached the shark, contacted him with its upper surface. The shark gave a convulsive shiver and was drawn unresisting into the substance of the monster. “