If you look inside the planter, there are two more turtles on the back of this "Squishy Turtle" by jakejake. Its bouncy legs and retractable head make it fun to play with. Feel free to copy and tinker with the model on Tinkercad.
Is this planet actually flat? If so, what holds up the Earth?
"Turtles all the way down" is an expression of the infinite regress problem in cosmology posed by the "unmoved mover" paradox. The metaphor in the anecdote represents a popular notion of the model that Earth is actually flat and is supported on the back of a World Turtle, which itself is propped up by a column of turtles. Questioning what the final turtle might be standing on, the anecdote humorously concludes that it is "turtles all the way down". (Wikipedia)
The file "Turtle Planter_Shell_Pot_V3" does away with the two bonus turtles, creating more volume in the planter for more dirt (or pencils or whatever). V3 will require some supports to be added underneath.
Tinkercad model of Turtle Planter
The original model was scaled up 209.4% in Tinkercad.