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.
The Thing About Jellyfish
Suzy postulates that Franny's death was the result of Irukandji syndrome after Suzy learns about jellyfish on a field trip to an unnamed aquarium, which Benjamin states is the New England Aquarium in the end notes. While researching the subject, Suzy identifies the following real-life jellyfish experts she thinks could ask for help: