what is it called when your fingers turn in shape after being under water for a long period
Most people would call that sort of thing wrinkled or maybe pruned, perhaps even corrugated if they were particularly prone to long words.
Wikipedia writes:
The wrinkles that occur in skin after prolonged exposure to water are sometimes referred to as pruney fingers or water aging. This is a temporary skin condition where the skin on the palms of the hand or feet becomes wrinkly. This wrinkling response may have imparted an evolutionary benefit by providing improved traction in wet conditions, and a better grasp of wet objects.
It's called (water immersion) wrinkling.