The answer is sea stars. Sea stars can then push their stomachs out of the body while inserting it into the prey thus the food is being digested externally. Echinoderms are having 5 or at times multiple of 5 arms. Their shell is made of calcium carbonate.
Oxidation and Reduction, I think? I may be wrong, I don’t really know what I’m talking about.... sorry if I’m wrong....
The ratio between the force of sliding friction and the normal force of an object is called THE DRAG
A theory possibly? Im not entirely sure because a theory needs to be proven over and over and over again.