sentences:  The head is roughened and flat, and the skin of the head is fused to the skull forming a casque; these features are often associated with phragmotic behaviour, in which an animal defends itself in a burrow by using its own body as a barrier.It has adapted its life cycle and method of reproduction to suit its environment.It also has a tough, impermeable skin which helps limit water loss, and a low basal metabolic rate which limits evaporation through its lungs.