09 November 2010

The twisted columella of Cecilioides acicula

Cecilioides acicula is a tiny land snail. It is native to Europe, but has been introduced to other parts of the world, including the U.S. (see this post for a record from Virginia).

I was skimming thru an old paper* about Cecilioides acicula earlier today when I noticed the following photograph of what appears to be a backlit shell.

What attracted my attention was the zig-zag path of the columella, the central axis of the shell. In the righthand copy I highlighted the columella with a yellow broken line.

I was under the impression that in most species the columella was straight. Here is a photo showing the columella of Albinaria anatolica (red arrows).

I may be totally mistaken, of course, and zig-zag columellas similar to that of Cecilioides may be more common.

*Wächtler, W. 1929. Anatomie und Biologie der augenlosen Landlungenschnecke Caecilioides acicula Müll. Z. f. Morphol. u. Ökol. d. Tiere 13:24.


Eric Corwin said...

That's really interesting, is there a reason why shells ought to have a straight columella? Or is it just that straight columella are always/often observed? Also, I wonder if that first photo is actually an x-ray of the shell, judging by the way that the shell appears darker where it would be offering up a thicker profile to the x-rays?


The German caption is: Gehäuse in durchfallendem Licht = shell in transmitted light.
I will attempt to duplicate the photo.

Anonymous said...

From what I have seen over the years, looking at cross sections and at x-ray images, a lot of columellas are pretty much dead straight, whereas others are more sinuous. The Ceciliodes one is particularly curving, thanks for pointing that out, I would not have noticed that otherwise.

I always used to enjoy finding this species when I was mapping the non-marine molluscs of Britain, in fact finding it was one of my specialities. It is a subterranean species, so I never actually found live ones in which the shell is completely transparent; I only found long-dead ones in which the shell had turned white and opaque. I found the shells in chalk or limestone areas, on the loose soil of molehills and anthills, and sometimes in flood debris of rivers. One of my favorite places to search for them was in churchyards. We called it the blind snail. I always thought the shells were quite beautiful.

Susan J. Hewitt

Eric Corwin said...

Wow, how cool that the shell is transparent! I guess there'd be no need for an x-ray in that case.