Starfish
The degree of protection offered by the skeleton differs between species. If the skeleton becomes more rigid, it offers better protection against predators. However, this will tend to limit its feeding alternatives. Great flexibility is required for the process of external digestion used by many species to eat bivalves. The less well armoured species may adopt a life in places where they are not so open to predation. The heavily armoured ones can tough it out in the most competitive habitats: