excellent capture, dito what jeff23. For the extra points - more DOF, slightly more light on the rhs, a little less of the dark underside more of the shell, I don't see no environment, you did this in a studio ;-)
nicely done. for my own taste (or a 10), I would have removed the line that runs from the centre of the head up and left on his shell - it is a small distraction. Also maybe a bit of reflected light into the area on the right of his head - but that is idyllic speaking - still a great shot.