Morphology of Electroreceptive Sensory Organs

Abstract

Abstract The morphology of electroreceptive organs in lampreys and their larvae, different fishes, water-living amphibians, and in monotreme mammals is described. The sense organs vary from superficial end buds in lampreys, ampullary organs in many cartilaginous fishes, bony fishes, and amphibians, to sophisticated tuberous organs in few groups of bony fishes. The sensory cells are also quite variable. In lampreys and many teleost fishes, electroreceptors are equipped with a bundle of apical microvilli. Cartilaginous and nonteleost fishes have electroreceptors with a single apical cilium, in some species surrounded by few microvilli. Caecilian and urodele amphibians may have both a cilium and microvilli. In all examined electroreceptive organs, only afferent nerve endings have been identified. It is generally believed that the electroreception arose early during the evolution of vertebrates. Apparently, this sensory modality disappeared during the evolution of teleost fishes, but was subsequently reinvented at least twice, most likely derived from mechanosensory lateral line organs.