08 February 2011

Protoconch of Helix aspersa

The protoconch of a snail shell is the apical portion of the shell that forms while the snail is still an embryo. In many species, the protoconch has a characteristic and species-specific morphology different than that of the teleoconch, the rest of the shell. However, it is not always easy to tell where the protoconch ends and the teleoconch begins.

Until tonight I had examined hundreds of shells of the land snail formerly known as Helix aspersa*, but not noticed how distinct the end of its protoconch was. The realization came to me when I happened to look at the following shell under the microscope.

This shell is an exception in that the demarcation between the protoconch and the teleoconch (arrow) is very distinct. Here is another and probably more typical shell.

Also notice that the surface of the protoconch is much smoother than that of the teleoconch.

*Now called Cornu aspersum, etc.


Cindy said...

I'd always noticed that tiny, whitish "beginning" part of the spiral on the Helix aspersa* snails in my yard, but didn't realize what it was. (Didn't think to look it up, either. Duh.) Thanks for the explanation.

*When and why did they change the name?


It was determined, I think on anatomical grounds, that Helix aspersa and another Helix species did not fit into the genus Helix. Thus it became necessary to move them into another genus. The problem has been picking the correct name for the genus to accommodate them. The name change has been going on for some time now, perhaps for at least 15 years or so.

Anonymous said...

When do snails grow their shells? Continuously, or only at certain times of day or after a particularly fruitful feeding? If it's incremental, is it those surges of growth that produce the ridges, or is it something else?


Shell growth s probably incremental and probably results in some of the finer ridges marking the periods of growth & rest. The more raised ridges probably form while the shell is growing.