Nematoda
About 80,000 species fall under the phylum Nematoda. Some scientists speculate that there could be many more species of Nematoda, numbering in the millions. The phylum Nematoda is the most diverse of the psuedocoelomates, and one of the most diverse of the entire animal kingdom. The round worm, perhaps the most commonly known species of the Nematoda phylum, have very developed nervous systems. The nervous system of the round worm is made up of a nerve ring that is made of four ganglia. From the ganglia, there are six nerves that run through their body. They are connected to different parts of the gut and some reproductive organs. There are an additional six more nerves that run through the body connected to the mouth.