Retrogressive metamorphosis is a type of metamorphosis where an active larva transforms into a sedentary adult, and the adult loses its advanced characteristics that were present in the larval stage. This process is the opposite of progressive metamorphosis, where an organism increases in complexity and develops more advanced characteristics over the course of time. Retrogressive metamorphosis is observed in some urochordates, such as Herdmania, where the larva bears all advanced characters of Chordata, but after metamorphosis, the adult loses its chordate characters. The process involves the destruction and disappearance of some of the larval structures, such as the long tail of the larva with caudal fin, which shortens and finally disappears. The anterior region between the point of attachment and mouth shows rapid growth, while the original dorsal side with atrio pore stops growth, causing the shifting of the mouth through 90° . The final branchial and atrial apertures in the adult represent the original anterior and dorsal sides of the larva.