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This document lists and describes the 9 major phyla of invertebrates: Protozoa are unicellular, Porifera are the first multicellular organisms, Coelenterata are aquatic organisms that have nematocysts, Platyhelminthes are flatworms, Aschelminthes can be parasitic or free-living, Annelida are segmented, Arthropoda have jointed appendages, Mollusca are soft and unsegmented, and Echinodermata are marine organisms with an endoskeleton. It welcomes upcoming scientists to learn about the key characteristics of invertebrate major phyla.Read less