Are snails born with shells?

Happy new year! I hope everyone is feeling suitably resolute.  I’m a bit weird with dates, so I’m not sure how I like the look of 2011 (2010 is much more pleasing on the eye) but that means I’m just going to have to try a bit harder to make this year excellent.

My next question comes from Jaz, and while I’m not sure I’ll be tackling whether slugs are ‘gutted’ not to be snails, hopefully I can quickly answer her other question.

Land snails build their shells, which are not permanently atttached, from minerals such as calcium from the food they eat. A tiny fraction of the adult snail shell called the protoconch – think of it as a prototype – is already present when the snail is still an embryo. When baby snails hatch from their eggs this shell is available to them and grows with them in a spiral shape – the oldest part of the shell is the centre.

The direction in which a snail’s shell spirals is genetically determined and in most species is clockwise. Scientists in Japan however have discovered that the rarer anticlockwise spiral can be induced experimentally, by manipulating the snail embryo at the stage when it only exists of four cells (the article I read suggested that this was carried out using a ‘glass rod’ however I suspect that the process was a little more complex).

This directionality, called chirality, is a property that features heavily in nature and science. Simply, chirality is the difference between our left and right hands. A chiral molecule lacks an internal plane of symmetry and has a non-superimposable mirror image – go on, hold your hands up and have a look.

So there you go – a small insight into the gastropod world. I’m pleased to say that this post had me worried I’d be looking at very uncomfortable images of shelly snail births but I’m relieved to find out otherwise.

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