In bilaterally symmetrical organisms (Bilateria), the transcription factor FoxO impacts stress response, lifespan, and increase in stem cells. If this transcription factor is knocked down in bilaterian model organisms, such as fruit flies and nematodes, their lifespan is significantly decreased. In experiments on "H. vulgaris" (a radially symmetrical member of phylum Cnidaria), when FoxO levels were decreased, there was a negative impact of many key features of the "Hydra", but no death was observed, thus it is believed other factors may contribute to the apparent lack of aging in these creatures.