Beetles. An order of the class Insecta.

• The outer pair of wings (elytra) is modified into a protective shell covering the inner pair.
• Biting mouth parts.
• Goes through a complete metamorphosis, egg, larva, pupa, adult.
• genitalia are retracted into abdomen.

They started out about 265 million years ago, in the permian period. At the same time, cockroaches, dragonflies, sharks, and lizards started, but none of them worked as well as beetles. Currently, at least one fourth (300,000+) of all known animal species are of the order coleoptera, making them the most prolific animal order on earth. It is possible that there are over 12 million speices of beetle.

References:
Natural Acts by David Quammen (recomended for anywho interested in nature)
General Zoology by A. Franklin Shull (ed.)
Integrated Principles of Zoology by Cleveland Hickman, Sr.; C.H., Jr.; Frances Hickman.
http://phylogeny.arizona.edu/tree/eukaryotes/animals/arthropoda/hexapoda/coleoptera/coleoptera.html (Very Good site for all insect stuff).

Co`le*op"te*ra (?), n. pl. [NL., fr. Gr. sheath-winged; sheath + wing.] Zool.

An order of insects having the anterior pair of wings (elytra) hard and horny, and serving as coverings for the posterior pair, which are membranous, and folded transversely under the others when not in use. The mouth parts form two pairs of jaws (mandibles and maxillae) adapted for chewing. Most of the Coleoptera are known as beetles and weevils.

© Webster 1913.