ABSTRACT
To escape from predators, the development and maintenance of strong skeleton/shell(s) in slowly motile/sessile invertebrates became inevitable during the checkered history of evolution. The skeleton/shells provide structural protection and are often essential components of morphological defense in the ever-escalating evolutionary ‘arm-race’ between prey and predator (Nienhaus et al., 2010). Not surprisingly, most aquatic invertebrates have developed an array of calcified ‘dermis’ (e.g. corals, crustaceans, echinoderms), calcareous tubes (e.g. polychaetes) or shells (molluscs). These defensive external skeleton/shells are further strengthened by the development of armor, spikes, spines and the like at a cost of energy, which otherwise would be used for growth and/or reproduction (Dodson, 1984). Even the relatively fast moving vertebrates like the coffer fishes, chelonians and crocodiles do have external skeleton.
