What does the pattern on the turtle's back represent …

There are different pieces of tortoise shell in different species, but even the tortoise shell is 13 pieces. Of course, the edge may be different, depending on whether there is a neck shield, that is, a small piece at the back of the neck, which some turtles do not have. The function should be: mechanical principle, the pattern is scattered and can't be broken ~ ~ Like cloisonne, some people say it represents the age, which I'm not sure about. But some people say that a turtle will grow another one in a year. I hope you can observe clearly.