The baleenus has grown in size due to its more efficient lifestyle. Its anus is now more baleen-like to capture microbes better. The upper part of its body extends further like a tail so that its back flippers can be flukes now. Its eyes are more complex and now have a lens. It only activates its fusion mechanisms for defense. Budding has been localized to the gills and the babies now start as very tiny plankton. Other than this it is similar to its ancestor.

A look at how the digestive tract of the Baleenus works.