The Centinger had a weirdly shaped body, with all its vital organs present within its centre, protected underneath its hard shell. As there existed nervous extensions to all vital information-gathering organs leading into the limbs, it resulted in the brain not being in a somewhat rounded shape as in all creatures but was instead elongated like a serpent with wings.
And to protect it existed a skull similar to the vertebrae of a human body. It was this skeletal structure that was treated as a skull counterpart by the Mind Extraction Prime Skill.
Inala transformed a Prana Bomb into a hollow cylindrical drill and began to puncture a way through its underbelly, spending a lot of time since the Centinger's body was ridiculously tough. 'If I fought it traditionally, it would have taken me forever to kill it.'