I know that you must be chomping at the bit for more information on snails, and I am here to deliver. However, I should let you know that this is going to focus more on snails in general, rather than focus on the European garden snail from my last post.
While the notion of of a snail carrying it's home on it's back is often depicted as helpful or wise, popular culture seems to miss out on a very important drawback of the snail's shell. That is to say that a snail's butt it located right next to it's head. The drawbacks to such engineering are obvious. And though you might be thinking of a land snail right now, this system is seems especially ill designed for any marine or freshwater snails who live in habitats where everything can just sort of, float around...
Why then, you might ask, would such a creature ever evolve? Well as it turns out, pooping next to your head doesn't much matter if you aren't alive, and shells are especially good at keeping you alive. Evolution favored a shell that was small and compact, yet could be drawn over the entire body in case of emergency. The spiral shell of a snail achieved exactly that. It is small, yet because of it's stacked spiral loops, the snail is able to fit a surprising amount of body mass into it. This design, however, came with a side effect. The snails entire internal body was essentially rotated 180 degrees in a process known as torsion, putting it's anus in that unfortunate position. The exact reason for this torsion has been the topic of some debate by scientists. It was hypothesized that the rotation helped to place body parts so that they would be easier to draw into the shell when needed. This hypothesis, however, has recently been challenged by the "asymmetry hypothesis" which says that the current gastropod (that's snails and slugs) body plan developed from a single side of what was once a bilateral body.
Still, despite their drawbacks, the snails body obviously works. They have become so numerous that entire sates have taken action to try to stop them. Even if you don't seem them directly, the marks they leave on household plants, or national-bound crops, are obvious. Yet, they lack a jaw, or even teeth with which to chew, so how do they cause so much destruction?
Gastropods, and molluscs in general, have (as they so often do) developed a unique structure specifically for this purpose. Located just withing the mouth, the radula consists of rows of chitinous "teeth" (yes, I know I said they didn't have teeth. What I meant is that they don't have proper teeth made of calcium. Theirs are made of chitin). Pulled in and out of the mouth by the muscular odontophore , the radula is feeding organ for the snail. Its teeth can scratch, scrape and cut away at its food, allowing it to become the insatiable "pest" that it is today.
Lots of words that you don't recognize? Well, welcome to the world of Biology.
If you have any more questions about snails or suggestions for future posts please let me know in the comments.
Almost all the information in this post came from: Invertebrate Zoology: A Functional Evolutionary Approach by Edward E. Ruppert and Robert D. Barnes
Additional sources:
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html
Modern Insights on Gastropod Development: Reevaluation of the Evolution of a Novel Body Plan
Integrative and Comparative Biology , Vol. 46, No. 2 (Apr., 2006), pp. 134-143
Published by: Oxford University Press
Article Stable URL: http://www.jstor.org/stable/3884787
good read keep it up!
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