Exoskeleton
Exoskeleton is a evolutionary innovation. This is operated by muscles attached to it and acts as an armor. Other than support this is an adaptive mechanism to provide protection against predators. In vertebrates, it is considered as the dermal bone that developed via membranous ossification. Fishes retained their exoskeleton in the form of their scales. However, in some organisms terrestrial evolution allows the loss of exoskeleton and formed a more mobile endoskeleton,
Since the average osmotic pressure of the brain is 300mM and the concentration of the solution is 280mM, that means there is 20mM difference between the brain cells and CSF. This will induce osmosis and cause water to move from the CSF into the brain until the concentration becomes same. Assuming brain volume is 1200ml and the CSF constantly replaced., then the estimation of fluid should be: 20mM/300mM * 1200ml= 80 ml
If it made percent it should be: 80ml / 1200ml= 6.67%
The Moon's mass is lower than that of Earth, thus it's gravity is less dense than Earth's gravity.
Since the strength and gradient of gravity is both mass and density it would be reasonable to think about mads