Porifera
More commonly known sponges the porifera date back to the Late Precambrian Period. The porifera group is characterized best by the different cell groups that function during the life cycle. There are around 5,000 species of Poriferans all of which do not have a nervous system. They rely on a constant flow of water through their pores to live. Since they all lack brains they cannot digest or remove wastes without the water. The nervous system is what makes organisms capable of reacting to its environment. Poriferans however lack that ability so most remain motionless except for a few that flow with the water.
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