Final answer:
FoxO is expressed in the nervous system of Hydra, a species within the phylum Cnidaria, known for their primitive nerve net.
Step-by-step explanation:
The FoxO gene is known to be expressed in the nervous system of Hydra, an organism belonging to the phylum Cnidaria. Hydra exhibit a simple nerve net rather than a centralized nervous system, with nerve cells scattered across the body. The nervous system in Cnidarians like Hydra plays a pivotal role in coordinating the behavior and functions of the organism. Although Hydra are simple creatures, they possess a well-organized set of cells for physiological processes. FoxO is a crucial transcription factor involved in the regulation of a number of biological processes including longevity, cell cycle arrest, and resistance to oxidative stress.