another interesting tidbit:

see how the tips of the manta ray's wings curl up out of the water? well, from a swimmer's perspective, those wings can look like the dorsal fin of a shark, and people often mistake manta rays for sharks.

as far as them being harmless... I have actually seen someone ride a jetski up to the manta ray, slide off the ski and onto the ray, and then hang on and ride until the ray dove down underwater. the ride was only about 50 yards, but it looked like alot of fun!