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.
Pain in fish
In 2002, Rose published reviews arguing that fish cannot feel pain because they lack a neocortex in the brain. This argument would also rule out pain perception in most mammals, and all birds and reptiles. However, in 2003, a research team led by Lynne Sneddon concluded that the brains of rainbow trout fire neurons in the same way human brains do when experiencing pain. Rose criticized the study, claiming it was flawed, mainly because it did not provide proof that fish possess "conscious awareness, particularly a kind of awareness that is meaningfully like ours".