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 amphibians
In 2002, James Rose, from the University of Wyoming, published reviews arguing that fish cannot feel pain because they lack a neocortex in the brain. If the presence of a large, considerably developed neocortex is required for experiencing pain, as Rose suggests, this theory would eliminate birds, amphibians, other non-mammalian animals, and even some mammals from having the capacity to experience pain. Other researchers do not believe that animal consciousness requires a neocortex, but can arise from homologous subcortical brain networks. Animal behaviouralist Temple Grandin argues that fish (and therefore, presumably, amphibians) could still have consciousness without a neocortex because "different species can use different brain structures and systems to handle the same functions."