27 February 2012

First butterfly of 2012

I saw the 1st butterfly of the year today during my after lunch walk. Here is the only picture of it I could take with my iPhone.

It was probably a cabbage white (Pieris rapae). According to Glassberg's Butterflies Through Binoculars, this species appears in New York in the beginning of April, in North Carolina in mid-March. Thus, seeing it in Maryland near the end of February is arguably a sign of the coming times.

May it find enough flowers to feed on and a mate to propagate its good genes.

18 February 2012

Suspended malacology

Suspending snail shells from pieces of string while sipping wine is a good way to spend a quiet Saturday evening at home. Only a few would disagree, I'm sure.

There is a deeper motive behind this activity, of course. I am trying to figure out where the centers of gravity of the shells are located.

Here is a marine gastropod shell hanging from a string with the columella (central axis) of the shell approximately horizontal (I don't know what the species is).

Here is another unidentified marine gastropod in suspension.

Finally, a land snail, a Cerion sp.

From the photographs, I've estimated the relative location of the center of gravity for each shell. The numbers from the base of the aperture and expressed as a fraction of the total shell length were as follows: 1st species, 0.37; 2nd species, 0.46; Cerion, 0.52.

Keep in mind that these numbers are from a single specimen for each species. There will undoubtedly be some within species variation.

I don't yet know what these number mean in terms of the shape of each shell. Various decorations present on some shells, for example, the spines along the lip of the 2nd shell, must also influence the location of the center of gravity. Also, the location of the center of gravity will probably be different when a shell is occupied by a snail.

06 February 2012

What does the inside of a snail shell look like?

Here is a shell of Batillaria minima with its inside exposed. It took me a while to remove the ventral side of the shell carefully with a small file.

The apexes of the shells of adult and most juvenile B. minima are normally eroded. Notice that the uppermost 3 whorls of this specimen are filled with shell material. The snail probably did that to strengthen the apex against further damage and also to prevent its body from getting exposed in case of additional breakage.

02 February 2012

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.