ABSTRACT
The Cnidaria are a group of animals that branched early in the eukaryotic tree of life, and they can be divided into five classes: Scyphozoa, Cubozoa, Hydrozoa, Anthozoa, and Staurozoa. The prevailing view of the nervous system in the freshwater polyp Hydra is that the neuronal network is simple and diffused throughout the animal’s body. Cnidaria such as Hydra is composed of multiple cell types that represent the fundamental architecture of multicellular organisms. Hydra exhibits a simple body plan with a single body axis. GLWamides have characteristic structural features in their N- and C-terminal regions. The presence of FLP-expressing sensory neurons in the planula larvae indicate that planula migration and metamorphosis may be regulated by the release of endogenous neuropeptides in response to environmental cues. Sexual reproduction in reef-building corals also involves motile planula larvae, which undergo complex metamorphosis after location of an appropriate substrate, resulting in the founding of a juvenile coral colony.
