MicroRNAs (miRNAs) are RNAs of ~21-24 nucleotides with pivotal regulatory roles in various developmental and physiological pathways. They inhibit the translation of mRNAs and thus constitute a “tuning” system for controlling post-transcriptional expression. While the understanding of miRNAs function in bilaterians such as flies, nematodes and mammals is expanding rapidly, little is known about miRNAs in other animals. The starlet sea anemone, Nematostella vectensis is a rising model which enables developmental biology studies in the non-bilaterian phylum Cnidaria under lab conditions. Recently, 40 miRNAs were found in N. vectensis but only one of them is a clear homologue of a bilaterian miRNA (miR-100). As the cnidarian miRNA collection seems significantly smaller than the bilaterian one, it is possible that the evolution of translation-control through miRNAs is responsible for the increase in morphological complexity observed between the basal cnidarians and highly diversified bilaterians (e.g. vertebrates and insects). We aim to study the miRNA expression patterns and function in Nematostella. Specifically, we will use in-situ hybridization, morpholino injection and transgenic manipulations to fulfill these aims. Once we have identified a miRNA whose knockdown results in a noticeable phenotype we will use various bioinformatic and experimental approaches to reveal and verify its target mRNAs. Since the last common ancestor of bilaterians and cnidarians has lived approximately 600 million years ago, common features in miRNAs and modulation of translation revealed in this work may be considered ancient. Intriguingly, it is possible that since this ancestor probably had simple body morphology and few cell types, the cnidarian miRNAs and their function resemble those of the common ancestor.