I don't know where this particular fella fits in the history, but turtles evolved from similar quadruped reptiles. Basically, their ribs evolved flat and wide so that their chests could support them better while burrowing tunnels. That turned into the turtle plastron.

Okay so is this photoshopped or what's going on here

Yeah this looks like a stupid degree of shrink wrapping of the neck.

I don't understand how they used it correctly and then didn't

Turtle shells are already on the inside. The entire surface of their shells is skin!

I can picture it now. An Ice Age movie where Sid, Manny, and Diego are hanging around a bar and this chonky boy shows up out of nowhere and makes an outrageous claim. Queue "It's Always Sunny in Philadelphia" music.

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