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.
Catostylidae
These jellyfish swim in jerks by contracting their circular and radial muscles, which decreases the volume of water enclosed under the bell, before relaxing them again and repeating the sequence. They have no control over the direction of locomotion and drift with the currents and tides.