Re: dose a sea snail have to hold its breath under water?

Hello,

Marine and freshwater snails don't have to hold their breath under water because they don't breathe air the way that we mammals do. Instead, aquatic snails extract oxygen from water using gills, in a way that is similar to what fishes do. If you have ever seen a fish that has been taken out of the water, you'll have noticed that it opens and closes its mouth repeatedly, as though it's gasping. And, in fact, that's what it IS doing -- gasping in an attempt to draw water over its gills so that it can breathe.

Isn't it strange, that we suffocate (i.e., drown) if forced to breathe under water, while aquatic snails (and fishes) suffocate if forced to breathe out of water? That's because lungs have evolved to extract oxygen from air, gills have evolved to extract oxygen from water, and neither works in the other's environment.

If you're interested in learning more about marine snails, check out this site from the Monterey Bay Aquarium. Click on the tab that says "Inhabitants," then click on "Invertebrates," and you'll find a long list of critters (including several snails). Each of the names in the list is a link to pictures and information on that species.

Another good source of information is The Marine Biology Coloring Book by Thomas M. Niesen. It's a lot of fun coloring the different exercises, and learning about marine biology while you're at it.

I hope this helps!

Allison J. Gong
Mad Scientist