Cnidarians represent the first animal phylum with an organized nervous system and a
complex active behavior. The hydra nervous system is formed of sensory-motoneurons,
ganglia neurons and mechanoreceptor cells named nematocytes, which all differentiate
from a common stem cell. The neurons are organized as a nerve net and a subset of
neurons participate in a more complex structure, the nerve ring that was identified in most
cnidarian species at the base of the tentacles. In order to better understand the genetic …