Thank you very much for your tips, I will try to fix the model, you are right, the detail level of the face it is too low and the brain maybe needs some detail added to it, about the rendered liquid, the inner liquid is green colored glass, I would like to share a previous attempt in Keyshot 5, where the material was liquid water, but when rendered the light could not reach through the different layer material (glass, water, skin) and iluminate the face (it was shown as black while the metal base and the spine rendered with no problems). I tried with Global ilumination (2.5) and number of bounces (32) with no luck.

Only if I turn the face, brain and tentacles as a non translucid material (like clay or plastic) the parts would show, like this:

Thank you for the help!