29 March 2006

Is it a Helix? Is it a Lymnaea? Or is it both?


The shell on the left belongs to the freshwater snail Lymnaea stagnalis, while the one on the right is that of Helix aspersa, a land snail. And here is what you would get if you could put the two together.


I found this specimen in the land snail collection of the Smithsonian's Museum of Natural History. Tim Pearce and I examined it briefly. We came up with 3 explanations as to how it may have been created.

1. It is a fake. If it is a fake, it is a very cleverly made one. As you can see in the picture below, the body whorl of Helix grew over the body whorl of Lymnaea. To be able to do that one would have to remove the body whorl of a Helix shell by cutting along the suture of the body whorl, put the rest of the shell inside a larger Lymnaea shell, place the body whorl of Helix on the outside and, finally, glue everything together without leaving any traces of the cuts and breaks.


2. Tim suggested that a juvenile H. aspersa in its shell was purposely lodged, or glued, inside an empty L. stagnalis shell. The Helix couldn't get out, so it grew out of the Lymnaea shell.

3. I thought that a H. aspersa was removed from its shell and placed inside an empty L. stagnalis shell. Somehow, it survived, reattached its columellar muscle and continued to grow, building its own shell. In Tucker Abbott's Compendium of Landshells (p. 193) there is a picture a similar chimera of H. aspersa. According to Abbott, in that case "an aspersa animal was placed in an empty Ennea shell and became atttached."

X-raying the shell would help pick between the alternatives 2 and 3. An X-ray photograph could even reveal hidden cracks and expose the specimen as a fake. All I could do at the museum was hold the shell against a light, but that wasn't helpful.

Note that the bands on the Helix shell are visible thru the translucent Lymnaea shell near the lip of the latter. This is explained (if the whole thing is not a fake) by the fact that when a snail resumes growth after a break, the new shell starts growing below the old shell and slightly behind the break. I have discussed this with examples in 2 previous posts (here and here).

I am not familiar with the name, Cailliaud, on the label. The only Cailliaud in 2,400 Years of Malacology is Frédéric de Nantes Cailliaud (1787-1869). If this specimen indeed belonged to him, then it is from before 1870. Cailliaud might have written about this specimen or others like it. I will appreciate any further information, including literature citations, that anyone might have on Cailliaud's work with chimeras.

8 comments:

pascal said...

Looking at this, I've been thinking: wouldn't the Helix regrow shell on top of the transition at the callous? I'd love to see this in person - but I bet an x-ray would really help show the structure.

AYDIN ÖRSTAN said...

I see what you mean. I have to think about that.

Chandrashekhar Phadke said...

I do not think that the specimen is fake. It is not possible to make specimen like this by any artisan. I have in my collection, an interesting specimen showing similar combination of Lightening Whelk and of Turbinella pyrum. The specimen is 28 cms long. and one can examine structure of large three pilae inside the whelk shell. I have not yet X-rayed the shell. I am from India.

Chandrashekhar
chphadke@yahoo.co.in

AYDIN ÖRSTAN said...

I don't think it's a fake either, but it is good to keep in mind the possibility that such unusual specimens could be fakes especially when they are found in unnatural places, such as museum cabinets.

firstmonsoon said...

Lovely blog, and vairy beautiful pictures. I haven't had the time to go through the entire thing yet, so bear with me - would what you learn of shells that you sea on land apply to seashell spirals too? I've been trying to look for info on the Nautilus shell spiral and what might prompt it to grow its shell in that way, so.

AYDIN ÖRSTAN said...

Although the same general principles apply to both sea & land shells, there are also some siginificant differences between them. For example, the shells of marine snails tend to be thicker than those of the shells of land snails.

Snails are gastropods, but Nautilus is a cephalopod, the class to which octopuses & squids belong.

Archana said...

I just realised I'd typed '..sea on land' instead of 'see..' heh.
Yes, and I think Nautiloids are supposed to be the only cephalopods with external shells, r something.

I'd like to know - does a snail's shell remain the same shape throughout its life? It looks that way to me, but I'm not very sure if I'm right or not about that. Does a snail's body always grow proportionately to its shell?

AYDIN ÖRSTAN said...

In most cases, the shape of a shell is more or less constant throughout a snail's life. But there are some well-known exceptions. Now that you mentioned it, I will prepare a post about that.

Your 2nd question is something that I have been asking myself.