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 papers published in 2017 and 2018 Michael Woodruff summarized a significant number of research articles that, in contradiction to the conclusions of Rose and Key, strongly support the hypothesis that the neuroanatomical organization of the fish pallium and its connections with subpallial structures, especially those with the preglomerular nucleus and the tectum, are complex enough to be analogous to the circuitry of the cortex and thalamus assumed to underlie sentience in mammals. He added neurophysiological and behavioral data to these anatomical observations that also support the hypothesis that the pallium is an important part of the hierarchical network proposed by Feinberg and Mallatt to underlie consciousness in fishes.