The organ is embedded in the skin of mormyrid fishes, which actively electrolocate by generating brief electrical pulses with their electric organ. The returns from the pulses, distorted by any nearby objects such as prey, are detected by the knollenorgans distributed around the fish's body.
A Knollenorgan is an electroreceptor in the skin of weakly electric fish of the family Mormyridae (Elephantfish) from Africa. The structure was first described by Viktor Franz (1921), a German anatomist unaware of its function. They are named after "Knolle", German for "tuberous root" which describes their structure.