I've come up against an interesting challenge recently. I've been modelling a tortoise character in Wings 3D and have arrived at a crossroads - should I settle for giving the character a modeled half shell on his back and then use a texture to suggest the other part of the shell on his belly, or should I model the entire shell on both sides? The latter option would certainly make him look more tortoise-like. However, in looking at real tortoises, I see that the construction of their shells curves very snugly around their legs, which works fine with a quadrupedal creature whose limbs are all for walking on and are all pointing at the ground. When you try and apply the same shell design to a bipedal creature with arms and legs, it doesn't fit - it is too restrictive. Particularly with a 3d character who is to be rigged in a 3d program, and who you want to be as flexible as possible.
In desperation, I've turned to the design of the Teenage Mutant Ninja Turtles, and have realised that, rather than having full turtle shells, they are sandwiches: each one has a shell on his back and a sort of orange breastplate on his front. In between, there is a dark green area that allows free movement of each character's arms and legs. It is a very sensible design, and one that I couldn't appreciate until I tried designing a similar character myself.
