Approximately 1.5 million different species of plants, animals, and microorganisms have been described and formally named. Some biologists believe this is only a fraction of species that exist; estimating there are more than 10 million species are waiting to be discovered, classified, and named. It is estimated that 15 percent of all species are marine organisms. Most scientists agree that only five percent of bacteria, fungi, nematode, and mite species have been discovered.