How Many Animal Phyla are There?
Under the most frequently used classification scheme, there are 38 animal phyla. Certain systematicists claim there are a different number of phyla, although always between 35 and 40. Only three phyla have been discovered in the last century, the most recent in 1993. No known phyla have ever gone completely extinct: at least some of their representatives always survive major extinctions. Most modern animal phyla show up in the fossil record during or shortly after the Cambrian explosion, an episode of adaptive radiation 630-620 million years ago. There remains disagreement as to how many of these phyla existed prior to the Cambrian explosion, during the Ediacaran period, though most scientists agree that at least eight were already established. The vast majority of animals belong to just nine phyla: Mollusca, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Echinodermata, and Chordata. In informal terms, these are the molluscs (112,000 species), sponges (5,000 speci
