23 October 2011

Ventridens suppressus and its mystery

Most land snail species that have teeth or lamellae in the apertures of their shells develop them as they near sexual maturity. In a handful of species, such apertural formations are present in young snails, but diminish in number and size or disappear completely in adults. The North American snail Ventridens suppressus is in the latter group.

The apertures of the shells of newly hatched Ventridens suppressus are unobstructed. Up to 5 lamellae develop in their apertures as the snails go thru their ontogeny. But as they approach maturity, the lamellae get resorbed one by one and the adults end up with 1 small tooth. Sometimes even that disappears completely.

Here is one individual that I found recently (shell diameter was ~5 mm). It has 2 lamellae in its aperture. This is Pilsbry's 3rd neanic substage (Fig. 235 in Land Mollusca of North America, vol. II:1).

In a paper that came out about a year ago, I hypothesized that in the aperture of the shell of the semi-terrestrial snail Pedipes ovalis, one long lamellae functions to protect the penumostome (breathing hole) from the movements of the foot.

I have long been puzzled by the lack of apertural formations in young shells and, in the case of species like Ventridens suppressus, in old shells. If they have a function, why are they not present at all life stages?

16 October 2011

A soiled Anguispira

The land snails in the genus Anguispira spend the winters buried in soil among the roots of trees. In November 2009, I wrote about 5 dormant Anguispira fergusoni that had become dormant for the winter.

A couple of days ago when we were looking for slugs in the park near our house, my wife discovered several of the same snails among the roots of a tree.

The shells of all the snails were coated with mud. They had probably been awakened from their sleep in the soil by the heavy rain we had had the day before.

I intend to go back to the same tree next weekend. I will search for the snails and if I find them, I will mark their locations in the soil with little flags. Then I will monitor them throughout the winter.

I also need to figure out a way to mark the shells of the snails for later identification.

09 October 2011

A box of plasticine

This tinful of plasticine tops the list of things I have used more or less continuously for the longest time. I bought it in London during a very short visit to England in September 1975. That was 36 years ago*.

I don't think I had a clear purpose in mind when I bought it. And for a long time I didn't do much with it. However, it gradually acquired a unique function in my photographic activities: I now use pieces of it to position snail shells when I'm photographing them.

Originally, each color was a separate stick. After years of handling, the colors are slowly amalgamating. I suspect 35 years from now there will be one mass of indeterminate color.

*The tin is not original; it's an Altoids box.

04 October 2011

Old Discus rotundatus

In the summer of 2008 when I was in Montreal for a few days, I collected some snail shells, which I later identified as Discus catskillensis, a species native to North America. There were, however, objections to my identification and knowledgeable readers proposed that the snails I had found were instead Discus rotundatus, a European species introduced to the U.S. and Canada.

After a long hiatus and with additional specimens collected last summer, I have now decided to pinpoint the identification of the Discus of Montreal for once and all.

I have at hand several lots of Discus species from museums that I will be comparing with the Montreal shells. Here are 2 lots of Discus rotundatus.

This one was collected in Sweden in July 1923 by someone named B. Sundler. Then it passed into the hands of R. Jackson before coming to the DMNH. I am not familiar with either of those names.

The 2nd lot is even older. It was apparently collected by a Mr. Schenk in Switzerland before joining the collection of Victor Sterki. Sterki (1846-1933) was born in Switzerland. So these shells may very well have been taken before Sterki emigrated to the U.S. in 1883.

Old museum shells with associated bits of papers that reveal the collectors names and locality data do have some nostalgic charm. Here is a related post.