30 November 2010

A skull only to be photographed

While searching for Pomatiopsis lapidaria in a wooded park last Saturday, we encountered a more or less intact and articulated deer skeleton. The skull with a pretty impressive set of antlers was still attached to the spine. Even the lower jaw was still in place.

I considered taking the skull home. However, it was not entirely clean. There were skin and dried tissue remnants covering parts of it; the cleaning operation would be quite messy and smelly. Besides, we were in a federal park and the removal of the skull would have been illegal. If I had had a large enough bag with me, I might have...but anyway.

29 November 2010

Some types of unknowable information

Whenever I see an old picture of a street scene or a landmark where some unidentified people are also visible, I usually wonder about them. Who were they? What did they do? What sorts of lives did they live?

Here is a street scene from the Galata district of Istanbul. The picture dates from 1888. Note the Ottoman gentleman walking side by side with a woman carrying an umbrella by the horse carriage.

So who were they? Where were they going? What had they had for breakfast that morning? Can we ever have answers to any of those questions?

It is possible in this case some of that information exists. The photographer or someone else who witnessed the taking of the picture might have known the identity of that couple and recorded it somewhere. And that record may still exist.

The couple by the horse carriage was Mehmet Baha Efendi and his wife Behice Hanim.

But it is much more likely that no such record was ever taken or if it was indeed taken, it has since been lost. Therefore, in all likelihood we will never know who those people were.

Not that it matters to know who they were. Even if I knew the information was available somewhere, say, in a library in Istanbul, I wouldn't bother to look it up. I don't actually need to have answers to any of those questions. What intrigues me is not the identities of the forgotten people of the old pictures, but the fact that the information about them is unattainable; it is lost forever.

We will never know who the people in the horse carriage were either.

28 November 2010

Pomatiopsis lapidaria on a cold and windy day

Pomatiopsis lapidaria is a small, operculated, semi-terrestrial snail. It has been recorded from several locations along the Potomac River near Washington D.C. Last year in December, I found it at Fletcher's Cove where the previous record had been by William B. DeWitt published in 1952 (see this post).

Yesterday we went on a field trip to look for Pomatiopsis lapidaria in Oxon Cove Park near the southwest corner of D.C., which was another one of DeWitt's locations. Although it was a cold and windy day, we had a productive field trip; we did find live Pomatiopsis lapidaria at the shore of Oxon Cove.

Because we didn't have a collection permit, we took only pictures of the snails.

We have no way of knowing if the snails we found were the direct descendants of the colony DeWitt had found in 1952. Nevertheless, our findings show that when a suitable habitat continuously exists at a location, Pomatiopsis lapidaria is likely to be found at the location.

26 November 2010

Mystery experiment goes down the drain

Taking advantage of the long Thanksgiving weekend, I decided to do some cleaning in the lab. Among the numerous dusty containers of snail shells, vials of dried up slugs waiting to be rehydrated and other odds and ends that I should I have put away a long time ago was a sealed plastic container. Upon opening it I saw a large empty vial and a microscope slide with 2 cavities each with a cap over it.

The empty vial must have held water once to prevent whatever was in the cavities of the slide from drying. The caps, now bordered with mold, must have also been placed to protect the contents of the cavities.

I removed the caps and examined the slide under the dissecting scope. The left cavity had a drop of a gelatinous substance covered with a layer of mold. I poked thru the gelatin, but there was nothing else I could see. The right cavity held a black paste-like substance also covered with mold.

There were no labels, sample numbers or dates anywhere on or in the container. That was surprising, for I am usually careful about marking specimens or containers.

I had no choice but to wash the microscope slide clean and discard everything else. This must have been an unfinished study. It will remain so.

25 November 2010

Color morphs of redback salamander sharing a tree

The other night while looking for slugs in the woods, we saw these redback salamanders (Plethodon cinereus) near the roots of a beech tree.

The leadback variant (left) was on one side of the tree, while the redback variant was on the other side.

Unlike most other salamanders that hatch out of eggs in the water and pass their juvenile stages there before leaving for land, the redback salamander spends its entire life cycle on land. Hence, it is referred to as a terrestrial salamander.

Being a very common species around here, this salamander has appeared on this blog several times. The previous post about it was here.

23 November 2010

A couple more big Megapallifera

My ongoing study of the population cycle of the slug Megapallifera mutabilis is still ongoing. The last post on this subject was here. I hadn't collected data since the beginning of August, because it had been difficult to fit slug collection trips into my schedule on days when the weather was suitable. But today's unseasonably warm weather and the light afternoon rain were a perfect combination. So after I came home from work, my wife and I went out to the local park at dusk to search for Megapallifera.

It was indeed a good night for slug hunting. Within about 30 minutes, we collected 14 Megapallifera from the trunks of beech trees. I brought them home and weighed them afterwards. They will be released tomorrow morning.

Here are the 2 biggest ones.

For those of you who must know, the distance from the tip of my finger to the middle of the visible joint is 5 cm.

22 November 2010

A disappointing Orwell collection

There are 14 essays in George Orwell, A Collection of Essays (Harcourt, Inc., 1981) and 6 of them are Orwell's criticisms of various English writers, including Dickens and Kipling, and of publications such as various weekly magazines for kids that were published in England early in the 20th century. As such, they are outdated and, I suspect, would be of little interest to most present readers. Another essay is about what Orwell thought of Gandhi, which, again, may not be relevant any more.

I enjoyed only 2 of the essays, Shooting an elephant and Marrakech. The first one is Orwell's reminiscences of a particular incident from his days as a police officer in Burma (Myanmar), while the other one is about his experiences in North Africa. In the latter piece, Orwell offers some interesting generalizations about the insignificance of the lives of most humans. Those had inspired me to write this post.

I also posted a slightly shorter version of this review on Amazon with only 2 stars for the book.

21 November 2010

Snail dissection in progress

Last night I started dissecting a snail that we had collected in Turkey in 2004. Here is the snail in its shell.

The specimen had, of course, been preserved in alcohol. The next picture shows the dissected snail. Next to it are the lower genitalia that I removed from inside the foot. I am always impressed by the size of the genitalia relative to the overall size of these snails.

Here is a closer look at the genitalia. I have labeled some of the organs. Keep in mind that this is a hermaphrodite: it has both a penis and a vagina.

This snail is in one of those speciose hygromiid genera in which the snails' shells are quite similar to each other and the differentiations of species depend primarily on the relative lengths of various parts of the genitalia, such as the ratio of the length of the penis to that of the epiphallus or the ratio of the length of the flagellum at the tip of the epiphallus to that of some other part.

I still haven't worked out the identity of this specimen. I am thinking of cutting open the penia next.

19 November 2010

Cochlicopa on the garage door—The finale

I started posting about the snails, Cochlicopa lubrica, on my garage door at the end of May (see below for links to the previous posts). The last time I checked on them was on 20 August when there were several of them stuck on the door. I thought they would take advantage of the fall rains and sooner or later descend to the ground. But then I started noticing that there wasn't much activity on the door even on rainy days.

Finally, 6 days ago I decided to investigate. There were 9 snails stuck to the garage door at various heights above the ground. Two of them, I noticed, had faded numbers next to them.

According to my notes, I numbered those snails on 13 August. So these 2 had not moved since then.

I removed all the snails and placed them in wet cups. About 8 hours later 2 had come out of their shells; the rest, shriveled up in their shells, were too far gone beyond recovery. The 2 numbered snails were among the dead.

I was puzzled initially. Why hadn't these snails climbed off the garage door to the greener pastures below where food and water were undoubtedly more abundant? Had they gotten stranded on the garage door during a dry period? But I think the explanation of these snails' demise is simpler: they were going to die anyway and they happened to be dormant on the garage door when they expired.

I am hoping a new generation will climb up the door next spring.

The previous posts:






17 November 2010

Lunch hour snails

I felt like looking for snails today during my after lunch walk. Fortunately the 1st spot I chose, a rotting, moss-covered railroad tie in a hedgerow alongside the railroad, had enough of them to satisfy me.

I found 7 empty Triodopsis shells and 1 juvenile Mesodon thyroidus in the soft, damp soil next to the tie.

These snails, especialy the Triodopsis, are quite common in that area. They are associated with the railroad. The crushed limestone used as railroad ballast is undoubtedly a factor in their proliferation. I suspect railroad activities are also somehow involved in their dispersal.

Although I have been collecting this particular Triodopsis for several years, I haven't yet bothered to figure out which of the many species it is.

16 November 2010

They don't make bookplates like these anymore

Earlier today I downloaded an 1897 monograph* about the land snail genus Pomatias from the Biodiversity Heritage Library. The book from which the pdf copy had been made was at the Mollusk Library of the National Museum of Natural History in DC. The opening pages of the book have 2 bookplates.

The 1st one belonged to William Healey Dall (1845-1927). He was the Curator of Mollusks at the NMNH for several years in the early 20th century. I have seen his bookplates in many books at the Mollusk Library.

Dall's bookplate features a land snail, a chiton, a couple of marine gastropods, a scallop and a squid, covering the major mollusk groups.

On the next page of the book is the bookplate of John Brooks Henderson (1826-1913). Henderson was a senator from Missouri. He also studied mollusks and even published papers on them. Politicians like him are nonexistent these days.

Henderson's bookplate is founded on several marine shells, including what seem to be scallops and cowries. Above them Poseidon, the god of the sea, and yes, with curvaceous hips, is rising out of the waters wearing his crown. His trident is in his right hand, while in his left he is lifting up what undoubtedly is a Tridacna gigas shell.

This was apparently the book #247 in Henderson's library. Dall probably inherited it from Henderson. After his death, it went to the Mollusk Library.

*Wagner, A. J. 1897. Monographie der Gattung Pomatias Studer.

15 November 2010

Shell shape changes in snails

The shapes of the shells of most snail species change during growth. Probably all snails when they hatch out of their eggs have a near-spherical shape, because their eggs are near-spherical (but here is an exception). As the snail grows, either the shell diameter or the height grows faster than the other dimension, giving the shell its final, adult shape. On top of the overall change in shape, the body whorl may descend as the snail nears adulthood further changing the shell shape.

In some species, however, the overall shell shape stays more or less the same during growth. Here is an example.

This is a Helix species. The shell on the left is, obviously, a juvenile, while the one on the right is an adult.

In the next photo I equalized the shell heights of the juvenile and adult shells and then overlapped their images. I also made the color of the juvenile shell reddish to make it easier to distinguish it from the adult.

The most outstanding difference between the juvenile and the adult is the area of the aperture, which is wider in the former. That is probably a universal characteristic of juvenile snail shells; shell aperture almost always gets narrower during growth. I don't know why.

14 November 2010

Marissa and the cricket

Soon after we moved into our house in the early 1990s, crickets followed suit and took up residence in the basement. They were probably house crickets (Acheta domesticus). I actually enjoyed sharing my house with them, because I found their incessant chirps during their courtship season, whenever it was, rather enjoyable; it felt like the wild outdoors was right there with us in the house. Moreover, they did no apparent damage, but provided entertainment to the cats who would go after them, although I don't remember if they normally ate them.

Then about 10 years ago, and for reasons unknown to us, those crickets disappeared and another species took over the house.

The newcomers are a species of camel cricket (family Rhaphidophoridae). I couldn't care less about the species turnover if the newcomers also provided musical entertainment. But they don't. That may be because they do their mating outdoors and come indoors only to take advantage of the the milder climate and the free food offered on the floors. Still, we tolerate them and don't normally bother them.

Occasionally, they do provide a diversion for Marissa Cat.

This particular encounter took place a couple of nights ago. For a long time, Marissa watched the cricket move about in front of her. Finally, she made her move, but the cricket went behind the curtain. Marissa chased, but the cricket went under a bookcase and that was the end of it.

Chalk one up for the crickets.

12 November 2010

A whole lotta Donax—Part 2

In the previous post I wrote about the 436 Donax shells I had once collected in Puerto Rico. In her comment, our regular reader Susan Hewitt asked if any of the shells had been drilled by the predatory naticid snails. As opposed to the irregular holes drilled by octopuses in the shells of their molluscan prey, the naticids (family Naticidae, moon snails) eat up their victims thru almost perfectly round holes.

A few of the Donax shells in my sample indeed have what appear to be naticid holes.

The following figure from British Prosobranch Molluscs by Fretter & Graham shows holes drilled in bivalve shells by the snails Natica (B) and Nucella (D). The former is a naticid, while the latter is in the family Muricidae.

Many more shells in the sample have chips at their edges. Here is an example.

I suspect those clams were preyed on by crabs.

10 November 2010

A whole lotta Donax

436, to be exact. I collected these bivalve shells at a beach in Puerto Rico in 1994. I believe they are Donax variabilis.

224 of the shells are right valves and 212 are left valves. I did a chi-square test and the difference was not significant (P=0.565).

What else can I do with them? Some have drill holes or chipped edges, providing evidence for predation. There are a few very small, presumably juvenile, shells. Perhaps, I can measure them all and look at the distribution of shell sizes. Or, maybe I can measure the volumes of a subsample and look at the change in shell volume during growth. What else?

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.

08 November 2010

3 leaves 3 trees

These are the leaves I picked up during today's after lunch walk. Their outlines may be superficially similar, but each is a different species. Nevertheless, the 1st 2 are closely related; both are maple leaves. The 1st one may be sugar maple (Acer saccharum), while the 2nd one is silver maple (Acer saccharinum). The last leaf is sweetgum (Liquidambar styraciflua). Its fruit, visible below the leaf, is covered with soft spines with openings between them.

There are about 6 Acer species in this area. Here are 4 maple leaves.

The 1st and 3rd are, once again, probably sugar maple and the 2nd one is silver maple. But I am not sure about the identity of the 4th one. Is it black maple (Acer nigrum)?

07 November 2010

An expired skink in my way

This dead lizard was on the path where I was taking my after lunch walk one day last week in College Park, Maryland. It was stiff and dry, surrounded by crusts of red stuff, probably its blood. It had been dead for many hours. This was a path frequented by bikes and one of them had apparently done it in.

If I am not mistaken, it is a five-lined skink (Eumeces fasciatus). Let my shoe be the scale.

The previous entry in this series of hiking path casualties was a northern brown snake.

04 November 2010

Ouch! Is that a snail shell stuck in her intestine?

A recent Google search on snails found a medical case report* about a 74-year old Spanish woman who had a snail shell stuck in her ileum, the terminal portion of the small intestine. The woman had swallowed the shell accidentally while apparently eating a Spanish dish called paella that contains snails. The woman was suffering from abdominal pain and vomitting when she was admitted to a hospital. Various scans revealed a foreign object in her abdomen, which was removed surgically and turned out to be a snail shell.

Here is a radiograph showing the shell in situ and a photo of it after removal.

Fig. 3 from Lerma et al., 2002.

I am not familiar with edible snail species of Spain, but this one may be an Otala sp. or perhaps, Eobania vermiculata. It's amazing that the woman swallowed the more than 3-cm long shell intact. She was lucky it didn't get stuck in her windpipe.

*Lerma, Marcos Agramunt; Mariscal, José María Errando; Cordón, Fructuoso Delgado; Abril, Segundo Gómez; Orón, Eva Montalvá; Pérez, María Jesús Martínez. 2002. Small Bowel Obstruction Caused by Snail's Shell: Radiographic and CT Findings. Journal of Computer Assisted Tomography 26:529-531. Abstract

03 November 2010

Volume of a snail shell

A subject high in my list of current interests is the measurement and the biological applications of the volumes of snail shells. Recent relevant posts are here and here.

The volume of a shell is a direct indicator of the amount of space the occupant snail requires. For that reason, I consider it a biologically significant property. However, shell volume is rarely used in research, probably because there is no easy way to measure it. One method that immediately comes to mind is to fill a shell with water and then to determine the volume of the water, preferably by weighing the shell before and after. However, this is easier said than done, because air tends to get trapped in the apexes of shells, which makes it very difficult to fill them completely with water. That's why empty snail shells float in water. Moreover, many field-collected shells have debris trapped in them, which also prevents them from getting filled completely. And because most adult shells are opaque, one can't see if a shell is clean or filled completely.

Here is a rare example of the use of shell volumes from the literature (Kemp and Bertnes, 1984).

This graph shows the relationship between shell volumes and shell lengths in 2 morphs of the intertidal snail Littorina littorea. The authors state that shell volumes were determined by "measuring the water holding volume" without additional details.

From general geometric considerations, volumes of snail shells (V) are expected to follow a power law in the form, V=cL3, where c is a constant and L is a linear shell dimension (for a relevant discussion see, Schmidt-Nielsen, 1984). If you take the logarithm of both sides of that equation, you'll get, logV=logc+3logL. In the graph above, the equation for line C was logV=-4.04+3.09logL. The equation for line E was similar.

Schmidt-Nielsen, K. 1984. Scaling: Why is animal size so important? Cambridge University Press.
Paul Kemp & Mark D. Bertnes. 1984. Snail shape and growth rates: Evidence for plastic shell allometry in
Littorina littorea. Proc. Natl. Acad. Sci. USA. 81:811–813.

02 November 2010

Variable leaves of tulip poplar

Autumn walks in wooded parks bring tree leaves in focus. Even though the leaves are dead, they can still present questions and answers about the evolutionary processes that brought them forth. Consider, for example, the shapes of these tulip poplar (Liriodendron tulipifera) leaves I picked up during a walk near my house the other evening.

I had never noticed before that the shapes of tulip poplar leaves were so variable. I am sure there are other shapes that I missed. These are the ones I noticed and picked up while trying to carry on a conversation on unrelated subjects with my wife. If I had paid any more attention to the leaves, she would have kicked me in the butt.

Can all or some of these variants be found on one tree or does each tree produce only one type of leaf? Does the shape of a leaf change during its growth? What is the functional significance of the leaf shape? Obviously, a leaf with fewer or smaller lobes would have a larger surface area for catching sun light than an equally long and wide leaf with more or larger lobes. These leaves were along a circuitous path no longer than about 2 miles, but the actual distances between the trees the leaves came from were much shorter than that. So the general environment of all the trees was the same. But, perhaps, the microhabitat of a tulip poplar determines the shapes of its leaves.