Before we move on, it’s probably important to see exactly what these two creatures even are before we do anything else!
What is a snail?
“Snail” is a loose term for a gastropod with a shell. There are land snails, freshwater snails, and saltwater snails, with at least some type of shelled gastropod in nearly every ecosystem in the world. Most of the time, the term snail is referencing land snails, but their aquatic counterparts can also be included, especially since snail isn’t a scientific term, but a popular one. Simply put, if a gastropod has a shell, most people will refer to it as a snail. Some snails can retract fully into their shells (many aquatic snails do this), but land snails generally can’t do this.
What is a slug?
Slugs are a member of the same taxonomical class as snails (gastropods). There are two groups of slugs, sea slugs, and land slugs. Sea slugs have minimal or internal shells and live exclusively in the ocean. The slugs that most people are familiar with, however, are land-based. They are totally soft-bodied and have no shells, internal or external. Slugs have all evolved differently, with many of them not sharing a common evolutionary ancestor. This form of convergent evolution (when two species evolve similar features without a shared common ancestor) produced different soft-bodied gastropods we call “slugs,” even though many don’t share evolutionary relationships with one another. Sea slugs and land slugs are great examples of this as they share a name but not an ancestor.
Are snails and slugs the same?
With all that information, we can finally answer the question: is a snail a slug with a shell? Well, sort of. A gastropod without a shell is known as a slug. A gastropod WITH a shell is known as a snail. What is clear, however, is that snails and slugs aren’t the same animals. Snails and slugs evolved differently; snails are born with a shell while slugs aren’t. Taking the shell off of a snail wouldn’t make it a slug; it would make it a dead snail.
Do snails need to replace their shells as they grow?
A common misconception is that snails find shells as they grow. While this may be true for hermit crabs, it isn’t true for snails. Snails are born with a small shell that slowly grows as they do. When it’s time for a snail shell to grow, they have a flexible material that expands the shell and hardens on the inside, adding layers over time. Taking a snail out of its shell will kill it, not turn it into a slug. Additionally, slugs won’t utilize shells, even if given the opportunity.
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