This required stronger bones, muscles, hearts, and ligaments. These animals evolved from small ancestors, gradually developing bodies that could deal with gravitational stress. Exoskeletons protect the body. They are light and very strong, and provide attachment places for the muscles inside. They protect the body from dehydration, predators, and excessive sunlight.
Exoskeletons lead to some difficulties, too.
The shell does not grow, so it has to be shed periodically. It is a struggle to get out of an exoskeleton, and the animal is vulnerable while the soft new shell hardens, which may take several hours. Exoskeletons are also difficult to repair if they have been damaged, although crabs and many insects can regrow a leg if they lose one. Exoskeletons are used by crabs, lobsters, insects and spiders. These animals are small.