Do snails turn into slugs?

Answered by Jarrod Smith

Snails and slugs belong to the same class of animals known as gastropods. While they share many similarities, there are some key differences between the two. One notable difference is the presence or absence of a shell. Snails have an external shell, whereas slugs have either no shell or a greatly reduced shell that is internalized.

The evolution from snails to slugs is believed to have occurred over millions of years. It is thought that as snails adapted to different environments and lifestyles, they underwent changes in their body structure, including the reduction of their shells. This reduction in shell size allowed them to move more freely and efficiently through their environment.

The process of shell reduction in slugs is known as internalization. This means that the shell, which was once external and provided protection, became internal and less prominent. The internal shell in slugs is often located near the back of the body and is greatly reduced in size compared to the shells of snails.

The reduction of the shell in slugs has several consequences. Firstly, slugs lose the physical protection that the shell provides. While the internal shell may still offer some degree of protection, it is far less effective than the external shell of snails. This makes slugs more vulnerable to predation and environmental hazards.

Additionally, the internalization of the shell allows slugs to have a more streamlined and flexible body shape. This enables them to navigate narrow crevices and move through tight spaces that would be challenging for snails with larger shells. The reduced shell also allows slugs to extend and retract their bodies more easily, giving them greater mobility.

However, the loss of a prominent shell also means that slugs have lost the ability to retract their bodies fully into a protective enclosure. Snails can retreat into their shells when threatened, providing them with a higher level of defense against predators. Slugs, on the other hand, rely on other mechanisms such as camouflage, slime production, and their ability to quickly move away from danger.

It is important to note that not all slugs have completely lost their shells. Some species of slugs still retain small, vestigial shells that are visible externally. These shells may serve little or no functional purpose but are remnants of their snail ancestry.

The evolution from snails to slugs involved a reduction in the size and prominence of the shell, eventually leading to its internalization. This change in body structure has both advantages and disadvantages for slugs. While they gain increased mobility and flexibility, they lose the protective benefits of a larger external shell. The diversity of gastropods, with both snails and slugs, showcases the fascinating adaptations and variations that have occurred throughout their evolutionary history.