Trilobites are wonderful ocean-bottom creatures that have been found in several of the geological systems of the Paleozoic, especially the Cambrian - so much so until the trilobite is called the index fossil of Cambrian rocks. Trilobites had extremely well designed eyes; as a matter of fact, the mathematical understanding for the trilobite eye was not even known until about 100 years ago. They are in the same group of creatures as are the dry land insects and could roll up their body like a pill bug(rollie-pollie). It is believed that when their fossils display their body rolled-up, they were attempting to defend themselves from the danger at the time of their death.