4. Conclusions
In both species, the mineral content increased from the carapace to the claw to the finger. This is explained by the different requirements for hardness. The finger is the movable part of the cutting device of the animal and must therefore be very hard. The claw is the fixed counterpart which must be more elastic, i.e. less mineralized. The carapace is the shell of the main body, i.e. it should be even more elastic to allow the movement and some bending of the animal. For comparable parts, the exoskeleton of the crab had a higher mineral content than that of the lobster. This is explained by the different escape behaviour. The lobster escapes rapidly and hides between rocks [17] and therefore should have a lighter, more elastic cuticle. In contrast, the edible crab clings to the ground or hides in the sand upon attack [18], and therefore needs a hard, highly mineralized shell. The fact that the lobster can swim whereas the crab can only walk supports that interpretation.