Type of electroreceptors = mormyromast I or A, ('small receptor'). It is an evagination of epidermal tissue on the lower side of the epidermis, sunk into the corium. The base is enlarged to an ampulla, surrounded by the sensory cells and opens to the outside by a narrow duct, filled with a mucoid substance. As the other mormyromasts the structure is surrounded by an ariole of the electroreceptor epidermis. Their function probably is passive electrolocation: reception of electric signals of other fishes, perhaps also spatial orientation.

Alternative forms for ampullary organ : mormyromast A, mormyromast I.