You know what, I feel like the shell part of the turtle is best represented by the "turt" part of the world turtle. It just looks the way "turt" sounds.
So a turtle without it's shell I think should start to be called a "le" (pronounced like in the world turtle), which represents very well, as a sound, a "turt"-less turtle
I also just noticed that the first "t" could be the legs and the tail of the turtle, while the "l" are the front legs and the "e" is the head and mouth.
Meaning that the shell part would actually be "urt".
More research is going to be needed to figure out this one.