Hox genes are highly conserved group of transcription factors that are responsible for patterning along a primary axis during development and are found in all bilaterians, an expansive clade representing over 99% of metazoan life. Cnidarians, such as anemones and corals, represent the only phylum outside of the Bilateria to have Hox genes, making them an important sister group for studying Hox gene evolution. Using embryos of the sea anemone, N. vectensis, we show using qPCR that Anthox6a is maternally expressed, suggesting that it may have a role in early development. Furthermore, Anthox6a is shown to be asymmetrically expressed along the future site of gastrulation when visualized with in situ hybridization. When Anthox6a is prevented from being expressed through the injection of eggs with an antisense morpholino, the treated embryo fails to gastrulate and endomesodermal markers are not expressed. This suggests that Anthox 6a has a fundamental role in allowing gastrulation to occur in cnidarians. Furthermore, when Anthox6a mRNA is injected ectopically into random blastomeres at the 8-32 cell stage, a second site of gastrulation including endomesodermal marker expression, is formed at the site of injection. This is the first case when ectopic expression of a Hox gene is able to establish a new body axis. This suggests that anterior Hox genes may have had fundamental roles in establishing the primary body axis in the ancestor of cnidarians and bilaterians.