Atolla jellyfish
The body of "Atolla wyvillei" is a bell shape and it has several moderately long tentacles along the bell. The bell is around 20–174 mm in diameter. It also has a single long tentacle called a hypertrophied tentacle. This hypertrophied tentacle has several purposes, including aid in predation and aid in reproduction. These jellyfish do not have a digestive system, a respiratory system, a circulatory system or a central nervous system. Not having a central nervous system means that it lacks a brain.
Hydra (genus)
The nervous system of "Hydra" is a nerve net, which is structurally simple compared to more derived animal nervous systems. "Hydra" does not have a recognizable brain or true muscles. Nerve nets connect sensory photoreceptors and touch-sensitive nerve cells located in the body wall and tentacles.