Metamorphosis is a biological process in which certain species of living organisms undergo havoc change in their physical appearance. e.g. mosquitoes lay eggs, it hatches & become larvae, which changes into pupa& then finally becomes an adult. Example of retrogressive metamorphosis is frog.

‘Retrogressive metamorphosis’ means degenerative changes wherein an active larva transforms into a sedentary adult. For example, in Urochordata, the larva bears all advanced characters of Chordata but after metamorphosis, the adult loses its chordate characters.

Retrogressive metamorphosis is the characteristics of Ascidians (Urochordates or tunicata). When an organism changes from a very advanced form to its primitive form then it is called retrogressive metamorphosis. In Ascidians, a progressive and active larva metamorphoses into a primitive sedentary adult.

Retrogressive metamorphosis is an attribute of urochordata in which an aquatic, free swimming larva with notochord transforms into an adult sessile, non chordate. Ascidia, Salpa and Doliolum are typical examples of Urochordata. The branchiostoma is a Cephalochordate, and the hemichordate animal is Balanoglossus.

During metamorphosis the larva will loose all the chordate characters and attains an invertebrate like form. This type of metamorphosis, where highly advanced larval form ends in a lowly organised adult is called retrogressive metamorphosis.

Metamorphosis is a term used in biology to describe a transition in shape, structure, or function. Even the transformation of spermatid into motile sperm is a type of metamorphosis. Retrogressive metamorphosis occurs when an aquatic, free-swimming larva with notochord transforms into a sessile, non chordate adult.

All the larval of echinoderms have a bilateral symmetry. Hence it is believed that the ancestor of echinoderms was a bilaterally symmetrical animal. Hence during Metamorphosis the advanced larva becomes a primitive adult. Hence the Metamorphosis is Retrogressive.

Retrogressive metamorphosis is a type of metamorphosis seen in Herdmania (and other urochordates). It involves transformation of an active, free swimming larva with advanced characters into sedentary and simple adult. So in retrogressive metamorphosis, retrogression or degeneration is shown by larva to form adult.

Retrogressive metamorphosis is characteristic of ascidians (Urochordata or Tuncicata). It is given this name because here a progressive, active and alert larva metamorphoses into a retrograde and sedentary adult.

Retrogressive metamorphosis is characteristic of ascidians (Urochordata or Tuncicata). It is given this name because here a progressive, active and alert larva metamorphoses into a retrograde and sedentary adult. Most of these characters are lost or become degenerate as the active larva metamorphosis’s.

Retrogressive Metamorphosis Metamorphosis is a change from the juvenile to adult stage in which larval stage is quite different from the adult stage. In retrogressive metamorphosis the larva possesses advanced characters which are lost during the development and the adult is either sedentary or degenerated with primitive characters.

It is probably due to the sedentary mode of life of the adult. Retrogressive Metamorphosis in herdmania or Ascidian follows disappearing of certain advanced characters of well developed larva towards the simplification of its organization.

Parasitic crustaceans, like Sacculina and copepod parasites and stylopids and scale insects (Insecta) also show retrogressive metamorphosis. The tadpole larva of Herdmania is only 1-2 mm long when it hatches out of the egg.

During metamorphosis besides retrogressive changes, certain progressive changes also take place. The neural gland is formed by the ciliated diverticula which have its origin from the anterior part of the pharynx. The pharynx enlarges and the number of gill slits is also increased. The stomach and intestine also grow in size.