Of what species is the following creature?
I expect it would be a Cephalopod living in not too deep water with a tropical climate (Brazil?). However, I can not find any information about what species it actually is.
While Ilan's answer has already covered the identification, here are a couple of other techniques which can be used to identify such animals in the future (or at least narrow down the scope of possibilities):
1: The upper left hand corner of the image depicts a fin which has multiple bony protrusions. This is an identifying feature of the Actinopterygii, which all possess such fin structures.
2: The image was not taken by you, but found online. In these cases, reverse image searches can be helpful in identifying the animal, since such reposts are often accompanied with identifying information.