“…The large, circular, centrally located nucleus observed in P. tandanus is characteristic of ampullary receptor cells (Zakon, 1986). The low number of receptor cells (10 -15) in P. tandanus resembles that of other freshwater siluroids (Herrick, 1901;Sato, 1956;Szabo, 1974;Gelinek, 1978;Srivastava and Seal, 1981;Zakon, 1986;Jakubowski, 1987), but is different from the hundreds of receptor cells per ampulla in P. anguillaris (Obara, 1976;Zakon, 1986).…”