As opposed to what arthropods have, vertebrates have this internal framework
.... 
a group of small arthropods that have six legs, three body .... Echinoderms have 
an internal skeleton-like framework made of calcium ... bilateral vs. radial 
symmetry. . [DOC] [TLE] Exoskeleton - New World Encyclopedia [PAR] Sep 15, 2008 ... A typical arthropod exoskeleton is a multi-layered structure with four ... in 
terrestrial arthropods, acts as a barrier against dessication.