Interesting subject. Your focusing is right on, the creature's
eyes, but Steven is right also in that the viewer is first
drawn to the shell and then travels up to the eyes. My suggestion is to use a higher f-stop to bring more of the
image into focus (a minimum of f8). Try focusing on the shell
first and then take a second image focusing on the eyes. You
might also try intervals up to f16. Anyway, just a suggestion.