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Spiders evolved different types of eyes, a pair of primary eyes that are usually forward pointing, and three pairs of secondary eyes that are typically situated more posterior and lateral on the spider's head. The best understanding of arthropod eye development comes from the vinegar fly Drosophila melanogaster, the main arthropod model organism that also evolved different types of eyes, the larval eyes and the ocelli and facet eyes of the imago. The gene regulatory networks (GRNs) that underlay eye development in this species are well investigated revealing a conserved core network, but also show a number of differences between the different types of eyes. Recent candidate gene approaches identified a number of conserved genes in arthropod eye development, but also revealed crucial differences including the apparent lack of some key factors in some groups of arthropods, including spiders. Here we use single cell sequencing (SCS) to overcome the bias of candidate gene approaches with the aim to identifying new genes involved in spider eye development, and thus to gain deeper insight into spider eye development, and arthropod eye development in general. Our main finding is that Hedgehog (Hh)-signalling is involved in eye development in the spider Parasteatoda tepidariorum, and by investigating embryonic gene expression in representatives of all main groups of spiders, we demonstrate that this involvement is conserved in spiders as a whole.