Nervous system is a defining feature of most metazoans. It consists of billions of neurons that provides sensory and cognitive abilities in animals to perform complex behaviors. Although nervous system has been at the focus of research for many years, the knowledge about its evolutionary origin is still in its infancy. What are the ancestral features of the nervous system and how it has originated and evolved over time to generate neuronal complexity in higher animals?To answer these questions, we are working on cnidarians that are placed in a phylogenetic tree as sister group to all bilaterians and therefore is a key to understand evolution of the bilaterian nervous system. Cnidarian nervous system is often described as “diffused nerve net” without a centralized brain. However, they share many fundamental properties with the bilaterian nervous system. Our single-cell RNA sequencing data suggests that the cnidarian Nematostella vectensis has around 24 distinct and differentiated neural cell types. We are currently validating our sequencing data and reconstructing the neural architecture of Nematostella by generating transgenic reporter lines that will mark different neural cell types. Additionally, we are also expending our genetic toolkit in Nematostella to establish them as the cnidarian model system. We have already established Gal4/UAS binary expression system and Flippase/FRT recombinase system to study neuronal complexity and its connectivity. The depth of this project offers comprehensive understanding of the cnidarian nervous system and will provide significant insights into how neuronal complexity has evolved in animals to perform complex organised behaviors.