The other kind of land snail

kw: species summaries, natural history, natural science, museums, research, photographs

I spent more than two years, in my work at the Delaware Museum of Natural History, cleaning up/correcting and loading data for their collections of terrestrial gastropods, informally known as land snails. Correction: the past 2+ years I worked with the pulmonate terrestrial snails. They are called "pulmonate" because they have lungs, though really they are modified gills in an internal cavity where they can be kept moist, and muscular contractions pump air in and out, like real lungs.

That is not the only kind of land snail. The other great division is the operculate terrestrial snails. They are called "operculate" because they have an operculum, a kind of door that they can use to seal the shell shut, to keep water in, because they have gills inside the shell, and also to keep predators out. Many marine snail species also have an operculum, used to avoid desiccation when they get stranded above the tide line for a while, and even more to keep predators out.

The pulmonate lifestyle is apparently the easier, because there are many more species of pulmonates than operculates. In the DMNH collection, 95% of the land snail collection is pulmonates, more than 40,000 lots versus about 2,000 lots or operculate land snails.

Thus, my last project is to clean up, and load, all the data for the operculates. The first major family that I encountered is the Annulariidae. Many of these have a flared aperture, as shown in these two images:

This image is roughly life size (the museum label is 3" long). The species Chondropoma bairense Torre & Bartsch 1938 is a little prettier than most of its kin, and larger. Here, "Chondro-" relates to "grain", and many species in this genus are little larger than grains of corn. The flared aperture is characteristic of species in many genera of the Annulariidae.

This one is called "bairense" because it was first found at Baire, Cuba, which is in the south, in the state of Santiago de Cuba, west of Guantanamo. Hoyo de la Reyes can mean "king's pit" or "-hole", but here it probably refers to a steep valley.

From the differences between the older label and the one that C.L. Richardson typed up we can see why it is helpful to have all the labels possible with a specimen. Richardson simply left out the name of the town on his own label!

Here is a closeup of the shells. Sadly, both have their tips knocked off. This is the only lot of this species in the DMNH collection, so we must make do with what we have. I find it fascinating that there is ribbing along the outside of the whorls, but the shell on the right also reveals longitudinal ridges in the omphalos (a synonym of "navel" or belly-button; it refers to the central hole where the whorls come together. Not all snail species have one, including the next one shown).

I picked one other species to show, because of its bristly appearance and because one shell still has the operculum:

In spite of the way the name is spelled on both labels, this species is Blaesospira echinus (Wright, 1864). The parentheses indicate that the genus name has been changed, but I don't know the history. I don't know what the genus name means, but I suspect it means something like "open spiral" because the whorls of the shell are not in contact.

The species name is easier: "echinus" means "spiny", and this little critter is truly spiny. The mogote (isolated hill) named "El Queque" is a well known snail collecting locality in the Viñales area of the state of Pinar del Rio, Cuba. 

This image is about 40% larger than life size; the shells seldom exceed a centimeter in length or diameter. These spiky little critters are even more impressive when magnified:

Here you can see that one of the shells still has an operculum in its aperture. Opercula frequently have a spiral structure like this one. The wavy rim of the apertures hint at the way the spikes are formed. They are hollow with open tips. These lovely little shells are very popular with collectors, which makes me wonder if they are still to be found there. Few specimens from Cuba have found their way into American collections since the Castro regime began in 1959.

I should also mention that some taxonomists place this genus in the family Pomatiidae (once called Pomatiasidae). What with DNA sequencing and other tools of molecular biology, the taxonomy of mollusks in general is being reviewed and revised more than ever. 

The waxy snails

kw: species summaries, natural history, natural science, museums, research, photographs

In the course of time I have come to a cabinet-and-a-half containing a couple of thousand lots of a family of snails (gastropods) named Cerionidae. Though there are four genera in the family, the Delaware Museum of Natural History holds members only of the type genus Cerion. The family was split out from a large family, Urocoptidae, by Henry A. Pilsbry in 1901. "Harry" Pilsbry spent much of his career at the Academy of Natural Sciences in Philadelphia, where he described hundreds (thousands?) of new species.



This first photo is of the type species (of the type genus of the family Urocoptidae), Urocoptis cylindrus (Dillwyn, 1817). Lewis Dillwyn originally named this species Turbo cylindrus, using a genus name created by Carl Linnaeus in 1758, when he single-handedly invented biologic nomenclature. At the time these specimens were collected the species was considered of the genus Cylindrella, then was shifted again to the genus Urocoptis when the family Urocoptidae was set up. The family Urocoptidae contains many genera, and while many of the species are similar to this one, being cigar-shaped with a flaring aperture, they vary a lot around this gestalt.

The genus Cerion, pronounced "kerion" or "Syrian", from the Latin word cerea, meaning "waxy", was named by Peter Röding in 1798, based on his renaming of Turbo uva as Cerion uva (Linnaeus, 1758). The genus has just a handful of fully accepted species, but the DMNH collection contains representatives of more than 200 species, which have varying levels of acceptance among workers carrying on a decades-long reworking of land snail families. This photo shows two characteristics of many Cerion species: the off-white waxy color and the ribbing along the entire shell. The flared aperture is less pronounced than it is in most of the Urocoptidae. The following photos showcase three more Cerion species, chosen to illustrate the range of variation in the genus.



The photo below shows Cerion weinlandi (von Martens, 1860); Edward von Martens originally placed it in the genus Pupa. It does look like a pupa! I chose this species to illustrate the extreme of nearly absent ribbing. Also, while the background color tends to be waxy off-white, this species is one of many with color banding and mottling also.



Though this lot is labeled Ceriod dalli Maynard—publication date is probably 1889—it was renamed and included in the species Cerion rubicundum (Menke, 1829). I don't know what name Karl Menke originally gave it. The species name means "ruddy", and when the shells are fresh and moist, the brown markings are reddish-brown. I chose this species for its narrow ribbing.



Finally, Cerion marielinum Pilsbry, 1927 (the museum curator attributed the species to Carlos de la Torre, who had edited the journal in which Pilsbry published the description) is so named for its occurrence mainly near Mariel, Cuba. This species shows wider, more robust ribbing, and also has a ruddy background with the waxy white being confined to the tops of the ribs.



I chose the scale for these photos so that they would show the shells close to life-size on a 17-inch monitor. On my 22-inch monitor they are about 25% larger than life. Comparing the four Cerion species with Urocoptis cylindrus, there is certainly a resemblance. It is easy to see why the genus was originally put in the same family. However, details of their morphology, including not only the more pronounced ribbing, but also the smaller aperture and the small teeth inside the aperture, distinguish Cerionidae from Urocoptidae…at least for now! Biological naming is always a tug-of-war between "splitters" and "lumpers". In some mollusk families, large numbers of species have in recent years been combined into a relative handful of species, and this may soon result in the few hundred species of Cerion being lumped into a smaller number of species that are recognized as being rather variable.

Genetic studies and breeding studies are going on in parallel, and revealing more and more about the species and inter-species relationships of many animals, not just snails. But, you know, I just like opening a drawer full of shells once in a while to simply admire them.

The most popular snails

kw: species summaries, natural history, natural science, museums, research, photographs

For the current series of projects at the Delaware Museum of Natural History, I have worked through several families of terrestrial gastropods (land snails and tree snails). Many of these are quite inconspicuous, being small and not colorful, though they are in general a little more various than the little brown "mud snails" (freshwater gastropods) I worked with for most of 2016.

You know, in any group of creatures, most are rather inconspicuous and poorly known. The "typical" mammal is a "little brown furry thing" such as a mouse, vole, shrew or lemming. The "typical" bird is a "little brown feathered thing" such as a wren or sparrow. The "typical" insect is a "little dark beetle" about the size of a grain of rice. The world is full of little brown things and we hardly notice them.

But we really like the colorful "charismatic" ones. Among the land snails, that would be the tree snails of Florida and the Caribbean, of the genus Liguus.

This is part of a drawer of "unidentified" lots of Liguus fasciatus, the poster child for pretty tree snails. Though these have been identified as to species, L. fasciatus has many "forms" or "varieties", which we provisionally catalog as subspecies, but they probably aren't really subspecies. We usually call them color forms.They hybridize freely, but a particular color form is usually physically separated from most others, being endemic to a few "hammocks", as small patches of raised and heavily vegetated ground are known in the area.

These are mostly from an area of the Everglades called Pinecrest, named for a ghost town tucked away in the middle of a couple of hundred hammocks. You can clearly see that most of these lots are in need of splitting into their color forms. Any particular hammock may be inhabited by a few color forms. A collector in a hurry will gather a couple of dozen shells, put them in a box or bag with a label (date, provisional ID, and location, at the least, to be a useful specimen lot), and move on to the next hammock a few minutes' walk away in the dry season, or a short airboat ride away the rest of the year.

Here is the prettiest of the color forms, in my opinion:

On your computer screen this may be a bit larger than life size. The paper label is 3 inches long, so these shells are about 2 inches long, a little bigger than the average for the species. Liguus fasciatus splendidus Frampton, 1932, must have been Henry Frampton's favorite also. These are indeed splendid! This lot was collected by Erwin Winte a few years after Frampton described them, and in the 1980's it wound up at DMNH.

These shells are so sought after that, though they are prolific and widespread, many color forms are getting hard to find. In the southeast U.S. and the Caribbean, a whole subset of shell collectors are called "Liguus collectors". We are loving them to death!

This only serves to introduce these lovely shells. I hope soon to gather pictures of several color forms, and also to compare L. fasciatus with its sister species in the genus.

The referential Clausiliid

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The gathering of biological species into genera (plural of genus), and of genera into families, can be a difficult matter. This is particularly true of animals that are variable in their expression, including mollusks, and gastropods (snails) in particular. The history of discovery proceeds to-and-fro: Species after species will be collected and described, and at first, many similar creatures will all be described under a certain genus. A later researcher may then distinguish a common set of features for certain of those species, and a different set of features for others, leading to setting them aside as a new genus. A similar but more arduous process is needed to discern family membership…usually.

In the case of a unique family of terrestrial snails, the Clausiliidae, one and only one distinguishing feature is needed to determine whether a newly discovered species belongs: the presence of a clausilium. This requires a little explanation.

You may know that many marine snails have a kind of "door" that they can shut behind them when they retreat into their shells. It protects them from many predators and also keeps them from drying out when they are exposed to the air for too long. These two pictures show different species of whelk; the operculum for each is visible. First we see a Lightning Whelk all pulled inside after a wave threw it up onto the beach. Its operculum is the brown oval thing in the aperture.

The second photo shows a different species of whelk crawling on the sand. The animal's foot, at the lower left, is white with dark spots, and the operculum is also brownish, attached atop the end of the foot. Many, many families of marine gastropods have opercula (the plural of operculum). Twenty families of freshwater gastropods also have opercula, as do a small number of non-pulmonate (that is, gilled) land snails. Only one prominent family and two very minor, though related, families of pulmonate land snails have opercula. A pulmonate snail has a lung rather than gills, or in addition to gills, and can thus spend prolonged amounts of time out of the water.

A clausilium is not an operculum. This structure is not kept external to the shell, as an operculum is, but is internal, as seen in these semi-transparent shells. Rather than being attached to the animal's foot, it is attached by a muscular structure to the columella, the central column around which the whorls of the shell are wrapped. When a Clausiliid snail retreats into its shell it pulls its body inside, then deploys the clausilium to block the aperture. So the clausilium's purpose is the same as that of the operculum, but is a distinct evolutionary development.

In addition, whereas an operculum is sometimes thin and even translucent, it is usually robust and may be a thick shell in its own right with a spiral structure. By contrast, a clausilium, although always calcareous, is thin and rather fragile. Apparently, members of the Clausiliidae, being small and having a small aperture, do not encounter the determined predators that attack many marine snails.

Today in my work on the current project at the Delaware Museum of Natural History I began to take inventory of a little more than 1,000 lots of the family Clausiliidae. The type genus of the family is Clausilia, described by Jacques P.R. Draparnaud in 1805. He based his description of the genus on the species Clausilia dubia, but a later evaluation by physician and malacologist Louis C.G. Pfeiffer led to a re-description of the genus as referred to Clausilia scalaris Pfeiffer, 1850. Ironically, this species has been renamed and then made synonymous with another species, and is now called Muticaria macrostoma (Cantraine, 1835; Cantraine originally called the species Clausilia macrostoma).

I found that DMNH has just one lot containing shells of this species, which is endemic to the island of Malta. The collector, whose material was obtained by Ralph Jackson in the 1950's and later donated to the museum, notes that this species is "very rare". Yet he somehow obtained six shells.

This photo shows the shells close to natural size. It is hard to see in this image that the shells are well-decorated with ridges or striations. Clicking on the image to see it larger is a little better, so I also took a closeup through a low power microscope.

The species name "macrostoma" means "large mouth". Clausiliids all have small apertures, and the aperture of this species is only "large" by contrast to many other species in the family, and that primarily because of the wide lip around the "mouth".

All the shells in this lot have the first one or two or three whorls broken off. That fact and the ridges indicate that these little animals live in a rather high-energy environment. I became curious about the locality so I looked it up, and found that Mistra is on a protected bay. Malta is not very large, being 17 miles long and 8 miles wide (27x13 km), but it has room for at least five places named "It-Torri", which means "red tower". The nearest to Mistra is about three miles to its northwest. This is a much windier locale than Mistra, so perhaps such environmental stresses shaped the species.

Few clausiliids are so heavily decorated, and, indeed, most are smooth or nearly smooth. So it is ironic for this to be, in effect, the "poster child of the Clausiliidae."

The yellow-tipped little agate snail

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Earlier this year I completed two major projects to prepare about 17,000 data records at the Delaware Museum of Natural History for all the freshwater species of bivalves (clams and mussels) and gastropods, and load them to a new database system from which they can be served up via the internet. The principal portal is iDigBio. A secondary portal, from which it is easier to dig into the records on a museum-by-museum basis, is InvertEBase. Each project took about a year.

That done, I have begun working through the museum's data for terrestrial gastropods (land and tree snails), which total about 38,000 records. We decided to take these a cabinet or two at a time, for the most part. I am basically tackling between 1,500 and 2,000 records per mini-project. A first project took about a month, so I expect the sum of about 20 projects to take a couple more years, maybe three or more.

I am in the midst of inventory for three related families, and the first is Achatinellidae. These snails were so-named because they resemble the large tree snails of the family Achatinidae. The prefix "achat-" means "agate" in Greek, and refers to the striped appearance of the most familiar species, the giant African tree snail, Achatina achatina (Linné, 1758), also called the tiger snail.

The one shown in this image may have a shell as long as 8" (20cm). The suffix "-ell" means "small"; the snails of family Achatinellidae are much smaller than the Achatinidae, but many have a similar striped look.

The type genus (the one the family's description is based upon) is Achatinella, and the type species is Achatinella apexfulva (Dixon, 1789). As I was taking inventory of the specimen lots of this species, I noticed that some had been collected by a major donor to the museum, Munroe L. Walton, when he was quite young, not more than eleven years old. In the three photos below, you can see they were collected in Hawaii in 1901; Walton was born in 1890. First, the photos, which mostly speak for themselves. Commentary continues following.

Around the year 1900 it was common to distinguish the many color variations of variable species by assigning subspecies names. The original labels for the first two lots reflect this. The third lot was originally attributed to a different species because many of the shells in certain parts of Oahu are left-handed, such as the one on the right in the third picture. These are now recognized as part of the species apexfulva. The suffix "-fulva" means "yellow", and shells of this species have a yellow tip. Specimens of this species grow to 1.5-1.9 cm (0.6-0.75 inch).

The second lot shown has an added label, written by Edward W. Thwing, who may have been the actual collector of that lot or part of it. He was 22 years older than Walton. The designations "New." and "Newc." on some of the labels refer to Wesley Newcomb, a physician who became a curator of mollusks at Cornell in the 1870's and until 1888. He described the first specimens of many species in the family Achatinellidae.

Although Achatinella apexfulva does not have a common name, I call it the "yellow-tipped little agate snail" as a direct translation of its scientific name. The Achatinellidae in general are colorful and attractive. Sadly, most, including A. apexfulva, are now extinct.

A snail family and a photo experiment

kw: species summaries, natural history, natural science, museums, research, photographs, digital darkroom

A few weeks ago I finished a project to clean up the data for all of the specimen lots of freshwater snails at the Delaware Museum of Natural History. We loaded almost 10,000 data records to the new database product, and linked them to the InvertEBase site (the link opens the Collections page; we are #3). Then I began working my way through the land snails (called terrestrial gastropods in most literature, and they include tree snails). The Curator and I decided to work taxonomic family by family, or in groups of related families, working with about 1,000-2,000 records at a time.

The two great groups of terrestrial gastropods are the Pulmonates (infraclass Pulmonata of class Gastropoda) and the Operculates (in class Caenogastropoda along with many freshwater and marine species). "Pulmonate" means they have a lung; "Operculate" means they have a small, separate shell with which they can block the aperture of their main shell when they pull inside, and this allows them to survive periods of dryness and also blocks most predators.

The majority of land snail families are Pulmonates, so we began with the family Ellobiidae and two related families, Carychiidae and Amphibolidae. Digging into current taxonomic research, I found that the family Carychiidae is now a subfamily of Ellobiidae, and is now named Carychiinae. I also found that, while a few species in family Amphibolidae are terrestrial, most are marine, and our collection contained only marine species. Nonetheless, having extracted the records, I proceeded with both families, dealing with 75 lots of Amphibolidae and 1,236 lots of Ellobiidae.

It is instructive to survey the family Ellobiidae, which tend to have a certain appearance no matter what environment they inhabit. Some genera are all terrestrial, some are all marine, a few genera are estuarine (adapted to brackish water), and others contain species found in various habitats.

We'll first look at Ellobium chinense (Pfeiffer, 1856). Lawrence Pfeiffer originally described the species under the name Auricula chinense, thus the parentheses around his citation, indicating the reclassification of the genus.

These are medium-sized, up to 3 cm long and 1.4 cm wide, and rather ovate or cigar-shaped. In the closeup below notice the small lump on the inner lip of the aperture. The apertures of nearly all species in this family are variously decorated, probably depending on the kinds of predators these snails encounter.

The genus Ellobium is primarily Asian, and this species occurs in Japan.

Here we have another strictly terrestrial species, Pythia pantherina (A. Adams, 1851). Though the genus of this species has been changed to Pythia, I don't have information what its earlier name was. (Scarabus) on the older label indicates a subgenus, now no longer used.

Shells of this genus have the most elaborate dentition in the aperture, which indicates they have more severe predation at the aperture, probably by birds. Such a wiggly aperture allows the soft-bodied snail to emerge and crawl about, but prohibits entry to all but the slenderest of bird beaks. Other predators have other ways in: see the shell at lower left in the closeup, with two tiny pinholes in its lower left area (I didn't notice them until I looked at the closeup). They are from a predatory drilling snail, which uses its abrasive radula (sort of like a tongue with tiny teeth) to scrape a hole through the shell. It then injects a nerve poison. The animal inside relaxes, and enough of it extrudes through the wiggly aperture that the predator can either dismember it in place or pull it out to be consumed.

The genus Pythia is found throughout the Indo-Pacific region, typically on mangrove roots above the high tide line, and a little further inland. These specimens, six of the eleven in this lot, are from the Sulu Archipelago of the Philippines.

The third species of interest is Auriculastra subula (Quoy & Gaimard, 1832); the genus was formerly Auricula. These are quite small, seldom exceeding 1 cm in length.

The closeup below shows a single tooth in the aperture on the inner lip, simlar to the Ellobium specimens above. This is an estuarine species, found on mangroves in tidal marshes. It is not fully marine and cannot tolerate ocean water for any length of time.

The genus Auriculastra occurs throughout the Indo-Pacific and South Pacific. These are from Fiji. They show more wear than the prior two species, indicating that they get roughed up in the sandy lagoons, probably during the frequent storms.

The fourth and final species is Ovatella algerica (Bourguignat, 1864), originally called Alexia algerica. These are very small, just a bit bigger than those called "minute", seldom exceeding 0.6 cm in length. Note, however that like the others they have the ovate/cigar shape characteristic of the family.

The closeup shows that they also have small teeth, in this case two of them, partially blocking the aperture. These are 8 of the 20 in this lot. The original label also shows a better example for future shell collectors than the other three: the town, the beach ("Quarry Beach" in Las Palmas), and the country, plus the month and year of collecting. Is lacks only the collector's name. I am not sure why an earlier version of the database placed these in Argentina, but I am glad it has been corrected ("Argentina" on the oldest label is in someone else's handwriting. The handwritten correction on the older DMNH label is from the 1990's.)

These species are found near-shore Europe and north Africa. Their habitats are fully marine to salt marsh. The Canary Islands are offshore from north-western Africa.

The photographic experiment I mention in the title is a matter of spacing for the sake of good focus. The typical way to photograph museum mollusk specimens is to arrange the specimens on black velvet, velveteen, or (as in 3 of the 4 cases above) on black felt, and then to arrange the labels and the scale indicator around them. But even the small shells of these Ovatella specimens have a significant thickness when being photographed close-up. One may either focus on the upper surface of one of the shells, or on the labels, with the consequence that the other will be a little out of focus. One way around that is to use a lens aperture of f/8 or f/11 for greater depth of field. I tried something different.

I cut a number of small pieces of corrugated cardboard, either 3/4" x 2" (2x5 cm) or 1/2" x 1.5" (1.3x3.5 cm). I put these under the labels to bring them up to a plane close to the tops of the shells. In the case of the Ellobium specimens above, it took three thicknesses of cardboard, and you can see the spacers under the smallest label in that photo and the first photo of the Pythia specimens. It worked very well! Everything I want to see is in good focus, using f/4 to f/5. I was also using a +2 closeup lens on my camera's 18-105 mm zoom lens.

With the camera back fixed at 24" (60 cm) above the table top, I used focal lengths of 36 mm and 105 mm. I used a spot focus just below the top of a central shell in each group for the autofocus to work with, and I am pleased with the results.

Each of the original images was cropped, and the color levels clipped to remove the grayness the camera allowed in the black background, and the gamma and saturation were adjusted so the colors in the image matched the colors of the shells. The images above are all re-sized to 1620x1080 pixels, so you can click on them to get images that fill most screens. I also used just a little bit of Unsharp Masking to emphasize the shell decorations, also to make the images look more "eyeball true". My Nikon camera under-sharpens its images, which I like. I usually prefer its usual, softer look, but when I want to sharpen back to "normal", UM is the most versatile way of doing so.

Finally, although felt is cheaper than velvet, the clean, smooth blackness of genuine velvet makes for much better final images, as can be seen by comparing the first two images with the other six.

The Great Pond Snail

kw: species summaries, natural history, natural science, museums, research, photographs

This tray contains all but four of the lots of Lymnaea stagnalis (Linnaeus, 1758) that are currently in the collection of the Delaware Museum of Natural History. It is called the Great Pond Snail because it is the largest freshwater snail found in Great Britain ("Great" in this case meaning "large"). L. stagnalis is the type species of the genus Lymnaea, which is the type genus of the family Lymnaeidae. You'll notice one box contains only a pink label. That indicates the lot is a Topotype; it was collected in the location where Linnaeus's first-described specimen (the Holotype) was collected. The museum keeps types in a special cabinet. I'll get into more about types on another occasion.

The Latin prefix lymn- is equivalent to limn-, which refers to a lake. As a matter of fact, I am a bit puzzled that the family is not named Limnaeidae and the genus Limnaeus (but see below). The species was first named by Linnaeus as Helix stagnalis. He placed nearly all the spiral-shaped gastropods he knew of in the genus Helix, for obvious reasons. Later workers broke up the genus into quite a number of new genera so as to group the species more appropriately. For a time, subgenera had been created to group the species, and in fact, Lamarck renamed this species Lymnaea (Lymnaea) stagnalis in 1799, while placing several other former Helix species into that subgenus; the subgenus name is in parentheses. Later genus-splitters removed the subgenus designation. In 1875, Sandberg tried to rename the genus Limneus, considering it a justified spelling correction. Nearly everyone else disagreed because of priority rules, and so Lymnaea it remains.

Members of the family Lymnaeidae are lake snails almost exclusively, and some are also found in slow-moving streams, such as in deltas. This species in particular favors very quiet, shallow waters, even stagnant waters if the oxygen content is not too low. Thus the species name stagnalis.

I chose to photograph two of the lots. This first, catalog #60565, was collected in a shallow part of the Niagara River, on the New York side. These are the largest specimens of this species at DMNH. I neglected to put the scale in, but the museum label is 1" x 3", so the largest specimen's height is about 2.3" or 57 mm. The largest recorded specimen just exceeded 60 mm.

These shells, being nearly translucent and very light in weight, practically broadcast their environment: very quiet water and an absence of shell-crunching predators. However, they are hosts to several parasites, and intermediate hosts to at least six different flukes, including one that can severely affect humans. Thus, these are well studied because of their medical and economic impact.

They are "ubiquitously holarctic", meaning they are found throughout the Northern Hemisphere, particularly at higher latitudes, though south of the permafrost line. They apparently hunker into the mud to over-winter in England, Scotland, across northern Europe including Russia, and across the northern U.S. and Canada.

The second lot shown, #119635, contains some of the smallest adult specimens in this collection. The longest is just over 0.8", or 21 mm. Although these were collected in 1926, this indicates that the river where they were found, in or near Detroit, Michigan, must have already been heavily polluted.

Note that both of these lots have subspecies designations on the collectors' labels; one was jugularis and the other, expensa. These are now deprecated; so far as I have determined, no subspecies of L. stagnalis are recognized at present.

The labels of the second lot also show its history, or most of it. Originally collected by L. F. Merrill, it came into the hands of Grace M. Seymour, and then G. M. MacCoy, who donated it to DMNH. Sometimes, collections are accompanied by letters and other documents that tell more of the story. I haven't dug into the library records for the MacCoy collection to see if there is more to the tale.

Shell collectors who are dedicated enough to identify and index and label their specimens are dubbed Shellers. By contrast, the designation Conchologist is reserved for those who also devote time to studying shells, and perhaps living mollusks, and professional Conchologists are called Malacologists. Mollusk enthusiasts and dealers Guido and Philippe Poppe have gathered information about more than 41,000 Shellers in their site Conchology Inc., from which they sell and trade shells, and curate a kind of online museum. It is one of a handful of online resources that I have found very useful to determine the full name of someone. Interestingly, however, none of these three Shellers is included. Neither is Esley Doremus, the donor of the lot from New York.

At least we have the initials for two of them and full names for the other two. In many cases I find a label that says nothing more than a species name, a location, and a surname followed by "leg." or "legit.", the usual Latin designations for a collector. The abbreviation "col." is also sometimes used, but "coll." usually means "from the collection of"; Shellers trade and buy shells so much that for many large collections, only a small percentage of the holdings were actually self-collected by the owner.

The 78 lots of this species held at DMNH allow researchers to study areal extent, presence through time at locations or in areas that were visited more than once, and changes in animal health. I occasionally find a note among the labels that specimens were collected from the bed of a dried-up pond, indicating at least local extinction. Rather poignant, that.

An apple-size apple snail

kw: species summaries, natural history, natural science, museums, research, photographs

I am presently checking and correcting geographic information for the freshwater snails in the research collection of the Delaware Museum of Natural History. Though I am not constantly using the lots in the cabinets, it sometimes happens that something I find in the database doesn't make sense, so I go to the lot in question to see what the collector, and perhaps later owners, have recorded. Today I happened to look up some "Apple Snails" of the genus Pila, and they are such nice-looking shells, and so much larger than many of those I've seen of late, that I just had to share a few of them here.

Firstly, here are two views of the largest specimen of Pila in the collection, and it ought to display at about 80% of actual size if your screen resolution is 100 dpi. The shell length, with the spire eroded, is about 5 inches, or 125 mm. The smaller item next to the scale is the operculum. Many snails have these; they are armored "doors" they can use to shut themselves into a shell when a predator threatens, or to avoid drying out during a dry season.

For the second view I turned over both shell and operculum. On this side of the operculum it is a little easier to see that it grew in a spiral pattern as the shell grew.

The original designation of this species was Ampullaria leopoldvillensis Putzeys, 1898. Sylvère Putzeys was a Belgian who collected in the Belgian Congo, as it was then called, and named this species for its type locality, which is now called Kinshasa, the capital of the Democratic Republic of the Congo (which was also called Zaire from 1971-1997).

I tracked down this specimen to be sure of the spelling of Coquilhatville. Then I was able to determine that the town is now named Mbandaka. It is about 550 km upriver from Kinshasa, and while I haven't looked it up, I suspect that snails of this species are found throughout the Congo river system. I understand that just one of these makes a good meal for a child, and two or three are sufficient for a teen or adult.

While I was in that cabinet, from the same tray I picked out two other lots to photograph, to show specimens of a more "average" size for this genus. This next species seldom exceeds 2 inches, or 50 mm, but is of a very similar shape and has a lighter color:

Pila globosa Swainson, 1822 is primarily Asian, and these were collected from the Mekong River system. The abbreviation of Swainson's surname is quite common. The better-known, more prolific naturalists were all abbreviated in field notes and earlier museum labels. L. means Linnaeus (or Linné), Lam. means Lamarck, Pfr. means Pfeiffer, and so forth.

As the name implies, this species is very globular, almost spherical. It is a contender for being the original "Apple Snail", but there are several others. All members of the family Ampullariidae are called Apple Snails, though not all are quite so globular. For example, this final species has a more pronounced spire:

The scratching-out and overwriting on the museum label, printed in about 1990, shows that the species now called Pila polita (Deshayes, 1830) was originally placed (by some authorities) in the genus Ritena, of the family Neritidae. The Nerites are mostly marine snails, but many species in that family inhabit brackish estuaries and quite a number are fully fresh water-dwellers. Sometime since 1990 this species was re-examined and re-named to be among the Apple Snails, to which it bears an even better resemblance when the spire is eroded, as in the third specimen in the top row. It is a pity we don't know just where in Thailand these were found. The Apple Snail website records these from Thailand all across south Asia to the southern part of China.

It is interesting that the original collector identified these shells as Pila, while the curator or collections manager who accessioned them into the collection used a different reference work to identify them as Ritena. Later someone else changed it back. So it goes. When all we have to go on are physical characteristics of a dry shell, convergent evolution can make two species look very similar when they are actually only distantly related, and in other cases a species will look quite different from its closest cousins because of rapid adaptation to changing environments.

Now that DNA sequences are getting almost cheap, museums are beginning to go through their collections to figure out just what species certain specimens belong to. There is usually enough DNA within the shell material to use with modern techniques, though at present one must destroy one or more shells in the process. This will change. Even more exciting times are on the way!

Two semi-related snails

kw: species summaries, natural history, natural science, museums, research, photographs

At the current stage of my inventory of the freshwater snails in the collection of the Delaware Museum of Natural History, I came across two species that  stretch the limits of the genus in which they have been classified. Indeed, as I shall discuss, they stretched those limits to the breaking point.

The first is Melanoides pantherina (von dem Busch, 1859). The genus Melanoides was created when a very large genus Melania was divided into several genera, and the family Melanoidea was broken into Thiara (to which these belong), Pleuroceridae, and several smaller families of genera.

"Melanoides" means "like Melania", and "Melania" means "dark". Snails in this genus are colored dark brown to nearly black.

This species was named "pantherina" because juvenile specimens are spotted. Faint spots in the smaller whorls of the specimen shown at right are still visible. At first, I thought the spots caused by their habit of laying their eggs on themselves were the reason for the name, but that habit is found in several related species.

Also note on the older label from Richardson's collection, that English and American conchologists tended to spell the author's name "Bush" instead of Busch. This arose during about a century of German-English conflict that culminated in two world wars.

The second species is presently named Melanoides Scabra (Müller), at least at Delaware, but many experts have renamed it Thiara scabra (Müller), and we plan to follow suit. The genus Thiara was created to gather the "Thumb snails", many of which really are about the size and shape of someone's thumb.

This species is a little smaller, but its lower spire indicates its affinity with other Thiara species. These species are also lighter in color than the typical specimen of Melania or Melanoides.

Both these species, and indeed, a great many of their relatives also, are river snails. Their shell shape and presence or absence of spines are clues to the energy of the rivers they inhabit, and the kind of predators they face. Larger, thick-shelled ones, for example, live in faster water and have little to fear from snail-eating fish, but are more likely to fall prey to boring predators such as smaller predatory snails.

The family to which they all belong, Thiaridae, is found throughout east Asia and the islands in the western Pacific and the Indian Ocean. They are found mainly in rivers and a few are found in brackish estuaries.

Tiphobia horei and photo testing

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This post is only incidentally about Tiphobia horei E.A. Smith, 1880, and more about the process of getting good photographs and making images that are both attractive and useful. T. horei is a freshwater snail that is endemic to Lake Tanganyika, which forms a major portion of the boundary between the Democratic Republic of the Congo (called Zaire for a couple of decades) and Tanzania; it also extends to the DRC's boundaries with Zambia and Burundi. The Delaware Museum of Natural History has two lots of this species, both collected in the mid-Twentieth Century. The lot shown below consists of two shells; the other lot has but one.

This image shows six presentations, obtained thus:

• The background for the column on the left is a black t-shirt I happen to have, though it has a giant Dupont company logo on the front.
• The background for the column on the right is a piece of commercial black felt. Closely looking at all the original images, I decided the felt is the better choice.
• The top pair of exposures is the normal exposure the camera's light meter indicated.
• The second pair was taken with a -1EV setting, and the third pair with -2EV. This was to be sure I obtained exposures that didn't have washed-out highlights on the shell. I needn't have worried.

I use Gimp (GNU Image Manipulation Program; GNU is a freeware consortium), a free alternative to Photoshop. The first priority here is to stretch the contrast to get the most out of the subtle hues of the shells, and push the background to black and the white on the scale card to fully white.

Here we have a lot of stuff in one image. On the left is the Adjust Color Levels dialog for one of the normal-exposure pictures. On the right is a crop of just its histogram, plus crops of histograms for the other two exposures. We can see how reducing the exposure just shifts all the tones toward black.

Three regions of interest appear in all three histograms. The peak on the left shows the range of dark grays from the background and the black part of the scale card. The peak at far right shows the near-white hues from the scale card. The bumpy peak near it shows the hues from the shells. The very low peak just left of center in the top histogram is from the penny. The clear separations make it easy to push the contrast as I desire. In the Levels dialog one just moves the little triangles at the bottom of the histogram to set the limits and adjust the gamma curve (which initially is 1.0). The following image is the upper right one from the montage above, just cropped to a tight square but otherwise unprocessed.

Here we can see, in addition to the shells and labels, the texture of the felt background. I used a stack of pennies to hold the tip of one shell up so the aperture is in the right orientation. By the way, the lower label indicates "40 m depth", but in the log book it says "40 mm depth". I suspect 40 meters is correct; this species is found anywhere from the surface to 100 m depth but is not common in shallow water. To obtain the next photo I set the contrast limits to 64 and 240 on the Adjust Color Levels dialog. I left the gamma at 1.0.

Now the entire background is solid black, the white of the ruler is at full brightness, and the color variations on the shells are much more distinct. Had I used a lower limit of 128 instead of 64, the pennies would also have become almost entirely black and the range of shell tones would be very strong, but it would look overdone. There is a lot to be said for working with the discriminatory powers of the human eye and brain, and not seeking to overwhelm them. For most purposes this image is a fine illustration of the shells and their labels. At times, such as for identifying shells that are more subtly similar to others, it is useful to increase the visible detail, thus I used one more processing step to emphasize the decorations and markings on the shells:

For this image I used a little bit of Unsharp Masking. It would usually not be a good idea to use this for a published illustration. The masking, a type of sharpening, emphasizes the fine details while lowering overall contrast. Unsharp Masking is one type of High Dynamic Range processing, and works even better when used with a Raw image. But a JPG image has 8 bits of color dynamic range, which comes to a 256:1 range, much greater than the typical 25:1 of a color print or magazine illustration or the 50:1 (at best) of a well made color slide. Thus we can often "pull out" details that would be lost if we just lowered the contrast overall.

Unsharp masking was developed decades ago for film processing, by astronomers who wanted to bring out details in photos of nebulas and galaxies, which have a very high contrast range. It consisted of making an out-of-focus copy of the negative, of the size you are going to make your print. That is the Mask. Then by printing through the mask, much of the large-scale dynamic range is suppressed, and the finer details are emphasized. It takes some experimentation to figure out how far out-of-focus you need to go to make the mask, and which level of contrast in the mask will appropriately render the image you want (when I was doing darkroom work I had five levels of contrast available in the printing and large-format negative films). It is time-consuming and expensive. The Unsharp Masking filter in Gimp and Photoshop and similar software emulates this process using computer code. One may tweak the controls on a dialog and see instant feedback.

As the label above also shows, these two shells were used to illustrate this species in the book "Best of Nautilus". It was a bit of an honor to handle them.

The Noble Hornsnail

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The image above shows all the specimens held by the Delaware Museum of Natural History for the species Pleurocera nobilis (I. Lea, 1845). From the lot-by-lot pictures below, you can see that two lots were originally identified as P. moniliferum (Lea, 1862). That species is now considered a synonym of P. nobilis. This species is found throughout the Tennessee River watershed, but particularly in and near that stretch of the Tennessee River running a hundred miles on both sides of the Tennessee-Alabama border, and into its tributaries.

When Isaac Lea named the species moniliferum, he was referring to a necklace, monile in Latin. With a length of at most 3 cm, this is hardly an impressive river snail. But compared to the rest of the genus Pleurocera it is larger and a little prettier.

Pleurocera means "ribbed horn", referring to the rib or ribs running along the whorls. In this species the rib is rather subtle. This lot of two shells was collected in or near the Holston River in Tennessee north of Knoxville, possibly quite far north, as that river is 160 miles long.

I took pictures for earlier posts on various backgrounds. Someone had said perhaps a standard gray would work, but I found that anything other than black or white tends to make the specimens harder to see. Today I used an enameled black surface, a background for one of the inspection microscopes. It worked pretty well but is rather reflective, so I guess it is time to spring for some black velveteen. I put paperclips under the specimens so I could orient them appropriately.
This lot and the next show how we occasionally run across misspellings and other errors on labels from collectors. "Bridgepark" actually refers to Bridgeport, a small Alabama city on the Tennessee River just south of the state border.

These were collected in 1877, as handwritten on the museum label, which was learned from Richardson's notes. He did not put collector or collecting information on his own labels, but fortunately had notes about many of the specimens he sold to the museum.

Being from a quieter part of the river system than the first lot, or the one that follows, these shells are a little larger and cleaner, not quite so banged up near the tip of the spire. If you'd spent a few weeks looking at other species in this genus, as I have, you would realize that when Isaac Lea named this species nobilis, he really meant it. Most of the pleurocerids are horn-shaped, but are usually rather small, and seldom undamaged. These seem "noble" by comparison.

This lot of three is also from the Holston River, though the original collector misspelled the river name. John D Parker, who gave these to the museum, didn't add his own label, so the volunteer on duty the day this was cataloged just used the spelling from the collector's label.


I included this fourth lot because when I saw it I thought, "It looks just like P. nobilis." These were found near Knoxville, probably at or near the confluence of the Holston and Tennessee rivers. Here is where habitat notes, so rarely made by a collector, might have helped us distinguish what species it really is.

Also, I could find no reference to a Pleurocera species named nodulatum, nor any variation such as nodatum, authored by Say or anyone else, and I don't know who identified it for Richardson or the person he might have obtained it from. There is nothing about that in Richardson's notes. But rather than re-classify it just now, I've put a note in the database that it may be P. nobilis, and to ask the next specialist in pleurocerids who visits to take a look at it.

A Genus at a glance

kw: species summaries, natural history, natural science, museums, research, photographs

In my work for the Delaware Museum of Natural History I have finished a side project that I began in April and returned to the inventory of the freshwater snails. I came across a genus that has very few species, and our holdings include just one lot each of the three most populous, a total of seven shells.

The genus Paramelania was originally named as a subgenus of Tiphobia by Edgar A. Smith in 1881. Although Paramelania has since been elevated to be a genus, Smith is the acknowledged author of the genus description, based on his work with the type species, Paramelania damoni (E.A. Smith, 1881). For this species the author reference is in parentheses because the genus name was changed by the elevation. Smith's original designation was Tiphobia (Paramelania) damoni. Our lot is shown on the left here, and in the following photo in a bit more detail.

A word about assigning scientific names. At the time Smith was working on African freshwater snails, the genus Tiphobia was considered a large genus with several subgenera. Smith had become familiar with exemplars of many of them. When he described the species damoni in 1881 he considered it distinct enough that he created a new subgenus for it within the genus Tiphobia. In 1898 John E. S. Moore described iridescens, and assigned it to the same subgenus. I have not determined which of two Boettger men (Caesar R. or his uncle Oskar) named Paramelania paucicostata, nor whether the elevation of Paramelania had already occurred. The author was probably C. R. Boettger, who spent time in Africa in 1914. Oskar was primarily a herpetologist, though he did describe several mollusk species.

The genus Paramelania, the genus Tiphobia from which it was extracted, and at least fifteen other genera are endemic to Lake Tanganyika in Africa. Lake Tanganyika is the largest of the African Great Lakes, being the second, by volume, in the world (Lake Baikal in Russia is the largest). At 676 km (420 mi) long and on average 50 km (31 mi) wide, and an average 570 m (1,870 ft) in depth, it is a huge lake, spanning more than five degrees of latitude. Imagine a long, very deep, skinny lake spanning the entire eastern boundary of Nevada! Lake Superior is three times as wide, only 80% as long, and not nearly as deep; its volume is less than 2/3 that of Lake Tanganyika, which hosts numerous habitats for numerous species.

This lot and the next were purchased by the museum from New Jersey shell collector Clarence L. Richardson in 1973, during the early days of the museum.

Here we can see that P. damoni has a rather heavy shell with modest ornamentation. Lake Tanganyika abounds with cichlids and other small- to medium-sized fish, and some of them eat snails. Snails that live in shallow water among the vegetation there need to be heavy-shelled to resist the bite of the fish. These two shells give only a hint of the variation found in this species. The aperture, in particular, frequently has a bit of a "wing" at the top, which we see in the next species.

P. iridescens is shinier and has a higher spire, but is otherwise nearly as heavily built as P. damoni. I have not read any ecology studies of these snails, so I can only speculate that this species inhabits slightly deeper water. The ornamentation is less, but the closely-spaced ribs add strength without adding excessive weight. Even for a small snail living in water, the weight of the shell is an important matter.

These two species are the only ones considered "approved" by the author(s) of the Wikipedia article Paramelania. However, the aggregating site Discover Life lists seven species in the genus, including our third exemplar:

P. paucicostata was named by Boettger for having "small ribs". These snails are very similar to P. damoni, although about 2/3 the length and 1/3 the weight. They probably inhabit either shallower waters, or a region more southerly than P. damoni, and the two species may never come into contact.

This lot was a gift of John H. Alexander, a few years before the Richardson purchase. These two men are among the big names on the earliest collections that laid the foundation for the 240,000-lot research collection at the museum.

We have few examples of an entire genus that fits in a shoe box, though a number of genera do contain but a single species. If we were to obtain specimens of the other four species that the contributors to Discover Life list in the genus Paramelania, our holdings would still fit in a shoe box!