Nice question :)
The most important feature of the skeleton of turtles is a large part of your spine is soldered to the back of the shell. The skeleton makes breathing impossible by moving the rib cage is done primarily by the contraction of the abdominal muscles so modified that function similar to the mammalian diaphragm and pumping movements faringe.
The skull shows characteristics of a great primitivism. Though it lacks teeth, have a horny beak covering his jaw, like the beak.
Like all reptiles, turtles are ectothermic, which means that their metabolic activity depends on external or environmental temperature.
Turtles shed their skin, but unlike lizards and snakes, they do little by little. Also move or off the shields of the carapace, individually and apparently no particular order.
Organization of the shields of the carapace of a turtle.
The shell consists of two regions:
Back: the top or dorsal (also called "shell"), and consists of five rows of plates, the central or neural, middle position, flanked on either side by rows sacks, which in turn are flanked by marginal rows.
Plastron, is the bottom or ventral (also called "dungarees").
The turtle shells are made of thick bony plates inside, which is ossification of the dermis that are welded to the vertebrae and ribs are an exception species Trionychidae family, in which the plates are reduced or are cartilaginous ( rich in calcium). On these bony plates, is one of the following covers:
Skin especially consistent, almost coriaceous (leather-like).
Horny plates of keratin, comparable to the scales of other reptiles.
Bone shields covered with a thin horny layer slightly calcified (only in the case of tortoises that is, the family Testudinae).
Turtles have skin lining are soft-shelled turtles (family Trionychidae) and pig-nosed turtle (Carettochelys insculpata). Also, the leatherback turtle (Dermochelys coriacea) is coated skin but strengthened with numerous small bony plates.
The rest of the turtles have a shell made of bony plates coated keratinous shields. These plates do not match in number, position or size with shields, and this is what provides rigidity and strength to this type of shell.
Turtles can not remove the shell, as shown in some cartoons, because the vertebral column and ribs are welded to it. The structure, shape and color of the carapace of turtles vary from one species to another.