The spermatozoon of Pecten maximus is of the primitive type usually associated with species having external fertilization or emitting the sperm in the water. The size of the nucleus is reduced. The middle piece is similar to that reported for several Bivalves. It contains glycogen. But the spermatozoon of P. maximus exhibits its own ultrastructural characteristics: the short acrosome differs in size, shape, position and ultrastructure or by a combination of these from that of many bivalves. No axial rods was observed in contrast to several species of Mytilidae, Veneridae and Ostreidae. These originalities could go to the genus level.