Invertebrates comprise 95 to 97 percent of the approximately 2 million species of animals that have thus far been identified. Despite the large number of species of which we are aware, we do not yet have any idea of their total numbers. In terms of diversity of species and lifestyles, invertebrates are unrivaled by any other animal group. Ranging in size from microscopic organisms to 66–foot-long giant squids, invertebrates of one kind or another are to be found in every habitat imaginable.