The invertebrate family which includes mollusks, worms and insects up 95 percent of all living animals.
Invertebrates have no vertebrae or backbone.
The invertebrates are considered to be more simple, or not as far along the evolutionary ladder than animals with backbones. Their simplicity has led them to be recognized by some as a lower form of life. Through simplicity their existence has allowed some invertebrates to survive unchanged for millions of years.