Mysteries of decollation

Here is a Euxina circumdata before...

and after it was decollated experimentally.


I wanted to know if the loss of a few whorls from the apex would let the snail lift its shell up during crawling. But, no, the decollated snail still dragged its shell.

There must be some other reason why some species decollate their shells.

Archaeo+Malacology Group Newsletter No. 20

The AMG Newsletter No. 20 is available here.

This issue starts off with yet another report on the land snail Papillifera papillaris. This time, Anette Rosenbauer is reporting it for the 1st time from Germany. The species, a native of Italy, was found in some stone-working yards.

There are also several articles by Henk Mienis about various mollusk finds at archaeological sites in Israel. In one of them, Mienis reports a mysterious accumulation of the shells of the marine snail Columbella rustica at a ruin.

In addition, there are the usual book reviews, lists of recently published relevant articles and the announcements of upcoming meetings.

Sleeping Cepaea nemoralis

Yesterday I returned to my Cepaea nemoralis survey grounds near Frederick, MD to check up on the snails after an almost 2-year break.

I encountered several dormant snails partially buried in the damp soil. Obviously, neither the dampness nor the unseasonably warm weather (air temperatures were well above 10°C) were enough to wake them up.

Two previous posts about dormant Cepaea nemoralis were here and here.

When barnacles were mollusks

This brightly colored picture of the gooseneck barnacle (Lepas anatifera) is from Edward Donovan's The Natural History of British Shells published in 1799.

Back then, and until the 1830s, barnacles were grouped together with mollusks, simply because they had shells as do most frequently encountered mollusks. Barnacles are actually arthropods, because they have jointed appendages like insects and their relatives. This post was about a barnacle on a snail shell.

Here is the title page of Donovan's book. It is available on Google Books.

Old Discus ruderatus

As part of an ongoing study, which is almost finished, I've been measuring shells of several species of Discus. Among the species included in the study is the European Discus ruderatus. Here are the labels of 2 old lots from the Carnegie Museum of Natural History in Pittsburgh.

The oldest date I can make out on the labels is 7/30/01; undoubtedly, that was 1901. And the stated location "Klausenberg, Transylvania, Hungary" was presumably the city of Cluj in Romania.

The 2nd lot was collected in Grisons, a canton in Switzerland, in August 1852.


The previous post in this series was about Discus rotundatus.

When taxonomy was much simpler

An excerpt from the entry for "Limax" in the 3rd edition of the Encyclopaedia Britannica published in 1797:

LIMAX, the Slug, or Naked Snail; a genus of insects belonging to the order of vermes mollusca...There are eight species, distinguished entirely by their colour; as the black slug, the white slug, the reddish slug, the ash-coloured slug, &c.

Observations of Deroceras laeve

One highlight of tonight's malacology-related activities at home was the filming of 3 individuals of the slug Deroceras laeve while they were having their meals.

The slugs, who had been starving for several days, were on a glass plate that I had coated with corn starch. They seemed to really enjoy the starchy meal. Here is a frame from a film footage of one of the slugs taken thru the glass and the starch layer.


The arrow #1 is pointing to the jaw, while the arrow #2 is, I believe, to the tip of the radula that the slug was using to scrape the starch off the glass.

Morphological scaling in snails

Here is the relation between shell volume, foot sole area and shell length for an intertidal snail.

In juveniles the foot is already shorter than the shell. During ontogeny the shell grows faster than the foot and so in adult snails the foot ends up being even shorter relative to the shell.

Note how much the rate of growth of the sole area lags behind the rate of growth of the shell volume. This is because volume is proportional to the cube of one or more linear dimensions, while area is proportional to the square of linear dimensions.

The interplay of volume and surface area and the resulting scaling effects underlie many evolutionary processes. For example, one reason why the smallest animals are all aquatic is that they lose their water content very quickly outside of the water, because their surface areas are very large relative to their volumes. At the opposite end of the range, the inner surfaces of the lungs of the largest animals always have convoluted morphologies, because the area of a flat surface would not be enough to satisfy the gas exchange requirements of the relatively much larger volume of the animal itself.

In the case of the subject snail, the consequence of this scaling effect is somewhat more mundane. When its shell gets too large relative to the foot, the snail can't lift the shell up anymore; it simply drags it behind its tail. In an earlier post, I discussed how this happens in the land snail Euxina circumdata.

This subject has had me preoccupied during most of my waking hours for the last month or so. In fact, I even lost sleep thinking over it one night. But finally, I am beginning to fit all the available pieces of the puzzle together.