Evolution of nervous systems
Jellyfish, comb jellies, and related animals have diffuse nerve nets rather than a central nervous system. In most jellyfish the nerve net is spread more or less evenly across the body; in comb jellies it is concentrated near the mouth. The nerve nets consist of sensory neurons that pick up chemical, tactile, and visual signals, motor neurons that can activate contractions of the body wall, and intermediate neurons that detect patterns of activity in the sensory neurons and send signals to groups of motor neurons as a result. In some cases groups of intermediate neurons are clustered into discrete ganglia.
Irukandji jellyfish
The symptoms of Irukandji syndrome were first documented by Hugo Flecker in 1952. They were named after the Irukandji people, whose country stretches along the coastal strip north of Cairns, Queensland. The first of these jellyfish, "Carukia barnesi", was identified in 1964 by Jack Barnes; to prove it was the cause of Irukandji syndrome, he captured the tiny jelly and allowed it to sting him, while his 9-year-old son and a lifeguard observed the symptoms (and then rushed him to the intensive care unit). Australian toxinologist Jamie Seymour made a documentary about the jellyfish called 'Killer Jellyfish'.