This ray hunts in the sand and moves by waving its wings.
It has a dart along its tail, which can be dangerous in case of bites on the man, but the blue spotted stingray don't attack, just be careful and don't hurt it.
This ray breathes through the top of the head and exhales from the bottom, allowing it to not suck sand.
Parrotfish create a protective envelope around them when they are sleeping.
So, don't put the light on them during night dive to don't to wake them up and break this envelope.
Mammals have a horizontal tail.
Fishes have a vertical fin.
Some sharks can stay motionless on the sand (white tips reef sharks, nurse sharks, etc.).
These sharks don't have to swim to bring oxygen to their gills like other sharks (grey, hammerheads tc.)