Hydra freshwater polyps are important model organisms in environmental and conservation science and evolutionary developmental biology. Scientists study the organisms because they evolved ∋600 million years ago, they can fully generate lost body structures, and their development is relatively simple and based on three stem cell lineages that give rise to ectodermal and endodermal epithelial cells, nerve cells, gland cells and nematocytes. These images show the individual motility of GFP-expressing endodermal epithelial cells in an asexually proliferating polyp (left) and the same organism one day later (right). Images reprinted with permission of PNAS. To better study cell movement in this organism, scientists need a transgenic Hydra line, but attempts at achieving a stable one have been unsuccessful. Now researchers from Christian Albrechts University in Kiel and from Max Planck Institute for Developmental Biology in Tübingen, both in Germany, have developed a stable transgenic line of Hydra vulgaris that expresses enhanced GFP. The method they employed may be extendable to other taxa such as Nematostella (sea anemone) and Acropora (coral). The transgenic Hydra on the left shows GFP expression in some of its endodermal epithelial cells, and the one on the right shows GFP expression in all of its endodermal epithelial cells. As published in the April 18 issue of PNAS, the researchers used the transgenic Hydra to study cell movement during budding and during regeneration. They think that the new transgenic line will reveal much about the model organism, and because the cnidaria phylum to which Hydra belongs is at the base of the metazoan phylogenetic tree, some information revealed about this transgenic organism may hold true to all metazoans.