Answer :
Nematodes
Nematodes (phylum Aschelminthes) have a high degree of centralization, with three-quarters of all nerve cells concentrated in a group of anteriorly placed ganglia and no peripheral plexuses or nets.
Nematodes (phylum Aschelminthes) have a high degree of centralization, with three-quarters of all nerve cells concentrated in a group of anteriorly placed ganglia and no peripheral plexuses or nets.