Bathypecten vulcani recently discovered in the 13 degree N hydrothermal area on the East Pacific Rise, is small in size, like other deep-sea Pectinacea. The genus Bathypecten is not restricted to this midoceanic ridge, but has another representative on sedimentary abyssal and bathyal bottoms of the East and West Atlantic, Bathypecten eucymatus . The main differences between these species concern microstructure and growth patterns. From its paleozoic affinities, Bathypecten may be considered as another "living fossil" in the East Pacific hydrothermal environment, but it clearly belongs to the adaptive radiation of a group of modern Pectinacea in which the separation between two distinct families is not necessarily justified.