Ever since we were children, we were fascinated by how caterpillars could become beautiful butterflies through the process known as metamorphosis. What most people don’t know, however, is that many species of invertebrates go through various stages of metamorphosis, either partially or completely. Although there are still many unanswered questions about how the process evolved and why some species only go through partial metamorphosis (or none at all), this entrancing quality has been thoroughly explored by researchers throughout the years.
Metamorphosis is essentially an abrupt biological change that some animals go through. This, of course, does not have anything to do with the changes and rapid growth that happens before birth or hatching, the process of metamorphosis essentially being accompanied not only by fast growth and nutritional changes, but by an entire transformation of the animal’s body structure through processes such as differentiation and cell growth. Certain species of insects, amphibians, fish, cnidarians and crustaceans are commonly observed to go through the complex process of metamorphosis, and the process itself, as well as the growth, behavior and nutritional changes that animals undergo are normally controlled through hormonal changes occurring in various stages.
Insects are by far the largest family of invertebrates, as well as one of the most diverse. Among them, you can find a large number of species going through both complete and incomplete metamorphosis, as well as those that do not undergo metamorphosis at all during their lifespans. Larval and adult ametabolous insects (insects that don’t go through metamorphosis) show only very few differences between each other, while many of their counterparts – species known to go through one or more stages of metamorphosis – show significant behavioral and morphological differences, some even featuring a pupal stage between the larval and adult stages of their development.
When comparing insects and marine invertebrates, there are a few striking similarities that can be observed in terms of their specific transformations. Most marine invertebrates go through a larval stage, just as insects do, and the process of metamorphosis can change many of the common traits related to their behavior, body and even their habitat. Since the larval forms of many marine species are able to move more easily, they often play a major role when it comes to dispersing the species’ population to far away areas. While many larvae tend to feed on plankton and other small animals, others develop a yolk sac, or carry other forms of nutrients, so that they do not have to actively feed.
Although metamorphosis is recognized as one of the most complex and efficient forms of biological changes, it is still quite uncertain as to how it actually evolved – especially in the case of insects. Ancestral insect species were observed to not undergo metamorphosis at all, while the study of some of the first insect species that have developed metamorphosis has caused many researchers to propose theories on the development and evolution of these changes that would have to be based on specific morphological comparisons and endocrine studies. Similar theories also exist, based on hormonal control and the study of a wide range of different invertebrate species; however, the precise means through which many forms of metamorphosis have evolved is, as of yet, still uncertain.