What are Trilobites?

        Trilobites were marine arthropods -- invertebrates (without a back bone). Trilobites thrived in an ocean environment and they were among the first arthropods -- existing before crustaceans, spiders, and
insects. Highly mobile, these creatures were among the first to develop a hardened exoskeleton.

    Many trilobites had large eyes. They are, in fact, the first organisms on earth known to have eyes. The trilobites had compound eyes, composed of many individual lenses, like those of insects. Trilobites possess the most ancient visual system known to scientists and thus they provided some of the best direct evidence of eye evolution.  Trilobites could see their environment and were always alert for the creatures that preyed on them.

       Trilobites are divided into three main parts: --

1.  Cephalon or head - Contains the bulk of the internal organs.
2.   Thorax - Contains the intestines and gill structures.
3.   Pygidium - contains the anus.

        Some trilobites developed extensive spines to ward off predators. Most typical were simple spines occurring as modifications of the head or tail regions. Some developed spines on the back of, or lateral projections from, the thoracic segments.