What is the most advanced phylum animal?

the largest phylum for marine animals is arthropods. arthropods includes shrimp,crabs,prawns etc. these animals have hard shell covering their body called exoskeleton.they have 3 under this phylum. crustaceans, arachnids and insecta.crustaceans include crabs,lobsters,prawns etc. arachnids include spidders that live in marine. and insecta include ocean skater.