Question

What is the difference between metamorphosis and retrogressive metamorphosis?

Answer 1

Hint: Metamorphosis refers to the transition of an organism from its juvenile to adult stage. A form of metamorphosis seen in herdmania is retrogressive metamorphosis. It entails the transformation of a sedentary and simple adult from an aggressive, free-swimming larva with advanced characteristics.

Complete answer:
Metamorphosis is the series of changes in the organism when it is transformed from the egg to an adult. It is regulated by the thyroid gland. Another type of metamorphosis is shown in case of urocheates. Let us discuss the difference between the two types.

Metamorphosis	Retrogressive metamorphosis
Metamorphosis is a term used in biology to describe a transition in shape, structure, or function. This may be an individual animal’s transition through various stages of growth, such as from hatching to maturity. 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.
A change in shape is often linked to a shift in behaviour or habitat	This form of metamorphosis involves the complete loss of advanced characters that existed during the larval stage.
Insects and amphibians undergo metamorphosis as part of their life cycle. For eg, dragonfly and mayfly larvae (=naiad) are aquatic and breathe through their gills, while flies breathe through their mouths and are airborne.	Some urochordates have avoided this path to retrograde form through neoteny, which means that their larvae do not display any changes associated with metamorphosis and, as a result, paedogenesis (sexual reproduction by mature larval form) occurs.

Note: The significance of retrogressive metamorphosis is that the advanced characters which were present in the immature stage will be lost. The juvenile or the larvae has all of the chordate characters like notochord, gill slits, nerve cord but it loses them when it transforms into an adult.