This study describes the microscopic anatomy of the reproductive systems of the keyhole limpets Fissurella latimarginata and Fissurella cumingi to test the existence of a possible isolating reproductive mechanism of morphophysiological type between species, and consequently to determine if the findings provide a valid taxonomic characteristic to distinguish these sympatric species. The results show that in both species the reproductive system is intimately associated with the excretory system. The gonad has a septa organization, and is connected with the distal portion of the right kidney by means of a renopericardial duct which functions as a genital duct. The gametes are evacuated to the mantle cavity through the right kidney opening. Besides transport of the gametes, the genital duct, which connects with the pericardium through the nephrostome, bears a gland attached to its inner wall both in males and females. No marked anatomical differences were noted between the reproductive systems of the two limpets which would allow their unequivocal taxonomic differentiation at the species level