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The origin of animal multicellularity is an enduring question in evolutionary biology - what innovations allowed our unicellular ancestors to evolve into complex creatures composed of thousands of cells? Cell adhesion, amongst other properties, is a fundamental requirement of multicellularity: to build an organism, cells have to be able to stick together. Despite major advances in our understanding of how mammalian cells adhere to one another, we do not know whether early animals used similar mechanisms to hold their cells together. This defense will describe a series of biochemistry and embryology experiments assessing whether the adhesive mechanisms operating in our own cells have a common ancestry with those found in the early-branching animal phylum Cnidaria (corals, anemonies, jellies, etc.), using the sea anemone, Nematostella vectensis.