Snails and Slugs Why do snails have shells and slugs Do not?

They look identical except one has a shell and one does not.

How does this happen? ANY science freaks out there or does anyone know this. Just curious

Snails and Slugs Why do snails have shells and slugs Do not?
Snails are just like crustaceans, they have their skeletons outside and their soft bodies inside.

Slugs are like amoebas.
Reply:They r similar looking species from the same family but are not same and are different from one another. We c many creatures sharing the similar characteristics but come from the same generic family. Both come from the family Gastropoda.



U'll find more info here and maybe u'd now understand the difference between these two species.

Slug is a common non-scientific word which is most often applied to any gastropod mollusk which has a very reduced shell, a small internal shell, or no shell at all.

http://en.wikipedia.org/wiki/Slug



The word snail is loosely applied to almost all members of the molluscan class Gastropoda which have coiled shells in the adult stage.

http://en.wikipedia.org/wiki/Snail
Reply:Interesting question! Actually, did you know that some slugs _do_ have a shell? It's very tiny and not visible externally, but if you look at such species, you'll notice a kind of "saddle" on their backs.

For example, this is a species of genus Limax, it has a tiny shell within its mantle cavity (internal):

http://www.dpo.uab.edu/~acnnnghm/BY255L/...



This is genus Veronicella, another common slug (shell-less):

http://floridana.typepad.com/weblog/imag...



The whole evolution of shells among mollusks is quite interesting. There are examples of shell-less forms (or with very reduced shells) in almost all the classes of mollusks, and the most remarkable are of course the cephalopods (cuttlefish and nautilus have shells, squids have a very reduced internal skeleton, octopi don't), but also the gasteropods. As you have noticed, snails have shells, slugs do not, and there are other, more spectacular examples of shell-less gasteropods: the nudibranchs or sea-slugs:

http://www.coastal.ca.gov/publiced/photo...



When studying evolution, one does not ask "why" something happened, what we try to do is understand "how" it happened. This is because we know that random variations arise all the time, what is more important is what were the selective pressures that made a given variation permanent.



It's obvious that both having a shell and lacking one give the animals different adaptive advantages, but also limitations. For example, if you have a shell, you're probably more protected, but you're also heavier. You need to "invest" more of your energy budget in building, maintaining and carrying your 'house'.

Now, in the case of slugs and snails, which are terrestrial animals, the problem of shell weight becomes especially serious (because gravity affects them more than their aquatic counterparts), so it seems logical that animals with small shells would have at least a locomotory advantage. If they could find other means of protection, then the stage for the evolution of shell-lessness was set (no, I didn't make up the word, I'm reading my copy of Brusca%26amp;Brusca "Invertebrates"). The reduction or loss of the shell seems to have occurred multiple times among snails.



Sorry for the long answer! But I hope it helps :-)
Reply:slugs are hobos ;(
Reply:First of all, Slug is a small slow moving creature with long slimy body. Snail is also a small slow-moving creature with slim body and a spiral-shaped shell on its back. They need this shell to protect themselves and at the same time it is their shelter.