Sensory organs, situated in the skin: cutaneous sensory organs, innervated by branches of the lateral line nerves. In Mormyridae there are three types: Mormyromasts type I or A or ampullary organ, type II or B and type C or knollenorgan or tuberous organ. They are surrounded by a particular kind of epidermis (electroreceptor epidermis), but restricted to the head, along the back and along the belly, up to the ends of the unpaired fins, but usually not on the flanks and never on the caudal peduncle. Gymnarchus has organs of similar function, also designated as type A to C, but of very different structure, also innervated by lateral line nerves. They are distributed all over the body, with exception of the tail, and also lying in a particularly structured epidermis.