A white slug from Tanzania

This "six inch long snow-white slug" was photographed recently by Daniel Hamlin on top of the rim of Ngorongoro Crater in Tanzania. The picture is posted here with his permission. I can't identify the slug. It could be an albino individual of a normally colored species. Any leads regarding its taxonomic affiliations will be appreciated.

Once again we apologize for the incidental loss of life

Empty land snail shells collected under the assumption that they are devoid of life forms—other than protists and bacteria, which are unavoidably expendable—upon returning home occasionally bring forth previously hidden occupants, sometimes with tragic results.

This morning, while examining a bag of clausiliid shells that I had collected in Istanbul in May 2007, I noticed a small, about 5 mm long, object covered with stiff hairs. It turned out to be another hapless snail shell dweller that had died in the shell bag while trying to find a way out.

The hairs and the pair of cerci identify it as a larva or a larviform female of the beetle family Drilidae. Here is a closer look at it.


The larvae of drilids are quite common predators of snails in Europe and elsewhere. After a larva consumes a snail, it pupates within the empty shell of its victim, a process that may take several weeks. That's why they appear in containers of otherwise empty shells sometimes many days after the collection.

This post had another example of a drilid from a bag of shells. A recent paper about the drilids of Turkey is Kundrata R., Bocak L. 2007. A revision of Euanoma and Pseudeuanoma (Coleoptera: Drilidae). Annales Zoologici, 57: 427-441 (abstract). This post was about isopods that came out of snail shells.

Just when you thought you didn't have any snails on you

Here is a lesson on snail dispersal:

One day lately I saw a friend of mine looking into a shop window in King-street. "What on earth have you got on your collar?" said I. He put up his hand, felt round his collar, and pulled off a big snail." "Well, I never," said he, "it was only half an hour ago when I was walking up Hunter-street that a friend stopped me and said, 'What is that you have on your waistcoat?' Lo and behold, there was a huge snail! The fact is" he continued, "I went down to see the water-lilies in the Gardens, and I remained there standing on the grass for a considerable time. These rascals must have crawled up my clothes when I was standing there." This is an excellent illustration of the manner in which snails are easily carried about from place to place...

W.S. Campbell. 1898. The Agricultural Gazette of New South Wales, 8:115.

What is the purpose and significance of comparative anatomy?

I am continuing to read F.J. Cole's History of Comparative Anatomy from Aristotle to the Eighteenth Century. While discussing the work of the 16th century anatomist Volcher Coiter, Cole first notes that Coiter compared the human skeleton with that of several other vertebrates and then presents a one-sentence criticism of his philosophy:

[Coiter] emphasizes, however, points of difference rather than homologies, and has therefore not fully grasped the purpose and significance of the comparative method.

From this we can deduce that according to Cole, the purpose and significance of comparative anatomy is to find anatomical homologies between different species.

A homology, or a homologous organ, is an organ that is similar in structure and position (but not necessarily in function) in 2 or more organisms and, which was inherited from a common ancestor.

Earlier in the book, Cole mentions, again in passing, while summarizing the similarities Pierre Belon noted between different bones of birds, an important caveat about the determinations of homologies:

[Belon] had no knowledge of the development of the skeleton, from which alone is it possible to homologize accurately the bones of the wing and the leg in birds.

To summarize, comparative anatomy gives clues about which organs may be homologous between different species (or within the body of one animal), but only by comparative embryology and development can we be sure of their homology.

This is one thing I like about the structure Cole's book: tidbits of significant insight scattered among biographical data or anatomical discourse.

The Assiminea I missed

In this post almost 3 years ago I wrote about how I hadn't noticed 2 tiny snails while photographing a much larger spider near them until later when I was looking at the photograph on the computer monitor. It seems that when we direct our attention to a particular object our brains has a tendency to ignore the nearby objects, especially if the latter are much smaller than the former.

Here is another example of this phenomenon once again involving snails. Last night, I was looking at the pictures of the intertidal snail Batillaria minima that I took last year in Florida. I hadn't examined many of the pictures critically until then. When I first looked at the particular picture below I decided that it wasn't very descriptive of the Batillaria that was the subject and decided to delete it. Then I noticed the blurry, brown thing near the right-hand corner.

That's an Assiminea succinea, another intertidal snail that spends most of its time outside the sea. This post has better pictures of them. The funny thing is at that time I was planning to collect Assiminea at another beach where I knew they were present. When I was photographing Batillaria they were there under my nose all the while, but I wasn't seeing them.

Shell color and shell repair in Batillaria minima

One of my favorite intertidal snails is Batillaria minima, already a subject of several posts, including this one and this one. Back in 2006, I published a short paper on shell repair in Batillaria minima and its relation to the retractibility of the snail into its shell (see this post for details).

At 2 locations near Tampa, Florida where I've been studying Batillaria minima, most snails have black shells. Occasionally, there are individuals with lighter colored shells, usually with green or brown tints. I suspect the green color is contributed by the microscopic algae growing on the shells.

Usually, ~20% of shells have repaired body whorls and ordinarily, the repaired portion of a shell is black like the rest of the shell. Here are 2 such shells; in the lower shell, the repaired portion is slightly lighter with a greenish tint.

Now here is a shell in which the repaired portion of the body whorl acquired a color much lighter than the original shell.


And here is a shell in which the opposite happened: the original shell had a light brown-green color, while the repaired portion ended up with the usual black color.


Finally, here is a shell displaying a peculiar color change. Something happened while the snail was building its penultimate whorl and the shell color suddenly changed from light green to pitch black. The spire also became slightly crooked, indicating that the snail had probably suffered some injury, but survived it.


I don't know the anatomical basis of how an injury triggers a change in shell color.

Busbecq's yellow balls

The cluster of 9 islands off Istanbul in the Sea of Marmara have long been known to the Europeans as the Prince or Prince's Islands. The Byzantine were in the habit of exiling the unwanted members of their royalty to the monasteries on them. Hence, their collective name. The residents of Istanbul call them Adalar, meaning "Islands" in Turkish. The 5 largest ones are inhabited, while the rest are not, at least not continuously; the smallest being an oversized rock 300 m across. The largest one, Büyükada (Big Island), which used to be called Prinkipo by the Europeans, has been the subject of at least 2 of my posts (here and here).

One of the first Europeans to write about the Prince Islands was Ogier Ghiselin de Busbecq, the Austrian Emperor Ferdinand’s ambassador to the Ottoman Sultan Süleyman the Magnificent in the mid-16th century. During a plague epidemic in Istanbul in 1561, Busbecq spent 3 months on Büyükada. In one his famous Turkish Letters, he wrote about his fishing expeditions off the islands:

Among the rest there is a small island, which is uninhabited*. Close to it I recollect capturing monstrous and extraordinary creatures, such as starfishes, razorshells, clusters of cuttlefish eggs, sea-horses, enormous snails, and some yellow balls like oranges, but no fishes, except one skate or sting-ray, which is capable of inflicting a serious wound with its sting.

Everything on Busbecq's list is identifiable (although I am not sure of the species of the "enormous snails") except the orange-like yellow balls. What were they? I am not familiar with the underwater life around the islands, but I suspect they may have been sponges of some sort.


*Probably Kaşıkadası, the Spoon Island, so called because of its shape. It is the 2nd smallest island. Google Earth shows a couple of buildings on it.

Cepaea nemoralis in Montreal

I was in Montreal last August for my niece's wedding. Besides spending time with friends and family (and even eating a snail), I also did sight seeing along a railroad and loitering in deserted parking lots behind buildings. The quest of my latter activities was the European land snail Cepaea nemoralis.

The results of my vacation research recently got published in the open access journal Check List. You may download a copy of it from here.

Cepaea nemoralis shells in Montreal.

An introduction to the history of science

My blooming interest in the history of biological sciences in general and of malacology specifically has led me to a 1944* book by F.J. Cole, History of Comparative Anatomy from Aristotle to the Eighteenth Century. I have been able to get a cheap used copy of it from Amazon. The 1st chapter has been highly readable and informative. Hopefully, the rest of the book will follow suit.

In the 1st paragraph of the 1st chapter, Cole laments the common lack of interest in the history sciences by the scientists themselves and then introduces a subtle warning (italics mine):

The scientist may admire, but cannot accept, the paradox that the beliefs and knowledge of antiquity have been superseded only by the more rational ignorance of to-day. It is thus the necessity of the man of science, if it is also his misfortune, to focus his efforts on the prospect that lies in front.

Cole goes on to explain why it is nevertheless good study the outdated, incomplete and often grossly mistaken science of our predecessors:

Wherefore let us bear in mind that this ancient knowledge still has its uses, if only as a warning of the dangers of research indifferently planned and weakly followed up. It behoves us therefore to examine the works of the early anatomists, to learn from them what we can, and, above all, to take heed lest we sow as they had sown and reap a similar harvest.

Well, I am for one following his advice.


*My copy is a 1975 republication of the 1949 edition.

No more photosynthesis

Goodbye fishie

Back in the summer of 2008, we got a small goldfish for my son. It lived in a large bowl in one of the bathrooms. It learned to recognize us and if it was hungry when someone was in the bathroom, it would come to the side of the bowl and start wiggling its tail rapidly. Occasionally, it would let me put my finger in the water and touch it.

After about a week of declining activity and appetite, yesterday evening it started lying on its side. A symptom of fishy homeostasis in distress. The only thing we could do was move it to a small container with fresh water. It survived with labored breathing for several more hours; in fact, righted itself up for a while. But when the morning came, it was a floating ex-fish.

And then it took the 1st flush to the waste water treatment plant.

Punctum and Cassis

The news of a YouTube video of a live Punctum minutissimum, one of the smallest land snails in the world—but not the smallest—have been circulating lately in e-mails as well as various facebook and blog posts. Here is a shell of of Punctum minutissimum. This particular specimen was 1.3 mm in diameter.

I took this picture last November when I was visiting the Carnegie Museum of Natural History in Pittsburgh for the 3rd annual meeting of the Ohio (River) Valley Unified Malacologists. When I was getting ready to photograph this tiny shell I needed something to place it on. So I used this huge shell of the marine gastropod Cassis madagascariensis. Let my hand be the scale.


Yes, the Punctum shell was sitting at the apex of the Cassis shell.


The contrast between the sizes of these 2 distant relatives is striking, isn't it? Cassis started out from a protonch, an embryonic shell, that was perhaps only slightly larger than the adult Punctum, but grew to be about 200 times larger than the latter. There are snail species that are even larger than Cassis madagascariensis and others that are even slightly smaller than Punctum minutissimum.

Are equally drastic size differences observed between the largest and smallest members of other animal groups? I will write about that in another post.

Here is a post comparing Punctum minutissimum to Neohelix albolabris, the largest native land snail in eastern North America.

Chemists do it with clamps - Part 2

After the toilet paper holder in one of the bathrooms at home fell apart the other day, I resorted to a quick and easy repair job with a couple of clamps.

In case you didn't take me seriously when I declared in this post that chemists can achieve a lot with a few clamps, maybe this example will drive the point home.

Simulation of snail dispersal - Part 2

I still have snail dispersal in my mind. In Part 1 of this series, I had assumed that the net dispersal distances* were normally distributed. Today, in a paper by Baur & Baur (1993), I saw a plot of the frequency distributions of distances moved per day by the land snail Arianta arbustorum in 2 different habitats.

Fig. 1 from Baur & Baur (1993). Left plot was for dispersal in a forest clearing and the right plot was for dispersal in a 1-m wide grassy strip.
The distributions were not normal at all. Baur & Baur fitted an exponential curve to their data. To simulate this distribution with my data from Part 1, which were normally distributed, I converted each dispersal distance to its inverse logarithm, thus creating a lognormal distribution.

Here are the lognormally distributed dispersal distances and their random dispersal angles in the form of a polar plot as in Part 1.


When dispersal distances are lognormally distributed, most will be near the origin, while a few will be far away from the origin. In comparison, in normal dispersal as in Part 1, most dispersal distances will be away from the origin and there will be more of them far away from the origin.

Do all or most snail species disperse lognormally?


*The net dispersal distance for each snail is the distance between the origin (the release point) and the snail's location at the end of the dispersal period.

Baur, A. and B. Baur. 1993. Daily movement patterns and dispersal in the land snail Arianta arbustorum. Malacologia 35:89–98.

The impression left by a pair of wings in the snow

While snowshoeing in the deep snow covering the soccer field near my house late yesterday afternoon, I saw these long, looping tracks ahead of me.

They were unconnected to any other nearby tracks. It was as if they had been left by a being that had descended from the sky and then ascended back into it. What could it have been?

A clue was present at one end of the tracks.


A winged descendant of dinosaurs!

Simulation of snail dispersal

I have snail dispersal in my mind. So I have done a simple simulation of the dispersal of a group of snails released at one spot using the following assumptions:

1. Every snail survives and disperses during the dispersal period.
2. The net dispersal distance for each snail is the distance between the origin (the release point) and the snail's location at the end of the dispersal period. The net dispersal distances are normally distributed. I have created the distribution data at www.wessa.net/rwasp_rngnorm.wasp.
3. The dispersal angles are randomly selected non-unique integers between 1 and 360 degrees. I have created the dispersal angles at www.randomizer.org/form.htm.

The plot below shows one simulation—the only one I have done so far—where I set the number of snails=100, mean dispersal distance=10, standard deviation=3.

Each data point could represent either one snail or one colony. The maximum dispersal rate of these snails during a given period, say a year, would be represented in this plot by those points that are furthest from the origin. In this simulation, the snail that was the furthest from the origin was 2.76 standard deviation units away from it.

The individual colonies are likely to have variable survival rates and those that are the furthest from the origin may be less likely to survive than the rest. (You think of some reasons why that may be so.) As a result, the boundaries of a snail's range at a given instance—represented by the outlying colonies—will fluctuate over time. Therefore, there may be an "effective" dispersal rate that is slightly less that the maximum dispersal rate. Perhaps we could equate the effective dispersal rate to the average dispersal distance of the points lying between a couple of arbitrary standard deviation units, say, 2 and 2.5.

Part 2

Temperature under the snow — Part 3

When life gives you lemons, make lemonade, when life gives you lotsa snow, go out and collect data. And that's exactly what I did last night following the massive snow storm we had. Once again, I measured the temperature under the snow, specifically repeating the measurements reported in this post.

Here was the set-up:

The yellow thermometer was a waterproof thermistor the probe of which was pushed to a depth of 60 cm below the surface of the snow to a point right above the top of the soil. The other one was also a thermistor for the measurement of air temperature right above the snow surface. Because the latter is not waterproof, I had to protect it by placing it into a plastic bag, leaving only the probe out. The Lean Cuisine pepperoni pizza box was functioning as a snow shield (it was still snowing when I started the experiment), while the cardboard tube covered with aluminum foil around the probe was functioning as a radiation shield (or so I hoped).

And here are the results:


Even though the air temperature dropped more than 10 °C, the temperature 60 cm below the surface of the snow was stable throughout the night. Once again, these data show how well an insulator snow is.

The observed insulation is probably due to the tiny air pockets trapped between the snow crystals. Since the soil temperature is normally higher that the air temperature, the measured temperature right above the soil surface remains higher than the air temperature above the snow.

Part 2 in this series presented temperature data as a function of depth below the snow.

Snow hanging down from roofs

The snow storm that started yesterday morning is continuing, although the best (or the worst, depending on your outlook) of it is over. The amount of snow that has accumulated will keep us busy tomorrow, despite the fact that my restless neighbors have already spent most of the day shoveling and blowing snow, while it was still snowing heavily. They even shoveled my driveway as I took pictures of them. Such nice neighbors.

Meanwhile, the snow along the edges of roofs have been hanging down in peculiar formations.

Here is another example.


And one more.


These hanging snow skirts have been quite stable during the last several hours. I suspect the snow must be rather sticky for it to be able to hang on like that.

Face to face with Pedipes ovalis

This is the 2nd post about Pedipes ovalis, a tiny (~3 mm long) semi-terrestrial snail that lives at the edge of the sea. The 1st post was here.

Here is a close-up of the front of the head of Pedipes.

It almost looks like the snail has a face, doesn't it? The black eyes at the bases of the tentacles are indeed eyes; but the "nose", the vertical, grayish patch, I believe, is the radula and the "mouth" below it is the jaw. Both the radula and the jaw are within the head, but they are visible because the tissues are transparent.

More will follow.

Invertebrate Rearing: a journal for rearing invertebrates

My facebook friend and fellow invertebrate enthusiast Ed Baker has recently started publishing his own open access, peer-reviewed journal, Invertebrate Rearing. Invertebrate Rearing publishes articles about the rearing and breeding in captivity of marine, freshwater and terrestrial invertebrates.

The 1st issue has 3 articles: the 1st one is about Australian jumping spiders; the 2nd one is about a British stag beetle and the 3rd one is about a parthenogenetic strain of crayfishes called marmorkrebs.

If you have raised invertebrates and collected enough data about their captive maintenance, consider submitting a manuscript to Invertebrate Rearing. Instructions for authors are available here. I may submit a manuscript in the future.

Ed also writes the blog Invertebrate Diaries.

Tentacle #18 is out

Issue No. 18 of Tentacle, the annual newsletter of the IUCN/Species Survival Commission, Mollusc Specialist Group, edited by Rob Cowie of the University of Hawaii, was released last Friday. It is available here, where all the previous issues can also be accessed.

This is the 4th Tentacle issue in which I have a piece that I first hashed out in one or more posts on this blog. This year's article (starting on p. 13), coauthored with Megan Paustian, is about the land planarian Bipalium adventitium and its interactions with slugs. The posts feturing that planarian are here, here, here and here and here.

There are many other good articles in Tentacle #18. Download a copy and read it now!

Sutures' futures

While cleaning the deer bones the other night, I noticed the intricate patterns of sutures on top of the skull. Here is the point, the bregma, where the 2 sutures join each other:

I believe in this picture the coronal suture is the vertical one and the sagittal suture is the horizontal one. My first thought upon seeing these sutures was that anything with their labyrinthine complexity can't possibly be reproducible and so their patterns must be specific to each individual deer, like the finger print patterns of humans.

Here is the sutures around the bregma of deer skull #2:


Deer skull #3:


Deer skull #4:


The patterns do change from skull to skull, at least in these 4 examples.

As soon as I figure out a technique of divination based on the reading of the deer skull suture, I will reveal it here for all in the future.