Joe.......About 71% of the Earth's surface is water, of which just over 96% of that water is ocean water. Considering how vast and deep the oceans of the world are, and how little of the ocean we have actually observed, I am not surprised at the size of some of the creatures that exist there. I feel confident we haven't seen the largest.
The giant oceanic manta ray is a species of ray in the family Mobulidae, and the largest type of ray in the world, 3,600 lbs (Adult), and reaches 7 m (23 ft) in width.