The mystery of the “Slitsnails”

Museo Malacologico Malakos

Believed extinct for about 65 million years but were discovered in 1855. To date (January 2018) only 35 species are known, but some are still uncertain. As far as we know, no museum in the world has them all, because some of them know only a few specimens. In the collections of the Malakos Museum there are as many as 23 species with over 60 specimens. 

Commonly known as the "Slitsnails", the members of this family (Pleurotomariidae) are among the oldest known gasteropods

Appearing in the Cambrian seas (about 500 million years ago), for a long time it was considered that this family had died out during the Paleocene (about 65 million years ago).

Today we know more than 1000 fossil species, but in the light of new knowledge, it is very necessary to have an accurate systematic review to eliminate the numerous synonymies.

Many times the bad state of fossil conservation makes some morphological characters, necessary for a correct identification of the species, invisible. The error of interpretation is always lurking.

The Pleurotomarie are characterized by a deep and narrow slot in the middle of the last turn.

As the animal grows fills the bottom of the slot, leaving a scar (selenizone) along the midline of previous whorls.

The slit has the purpose of allowing a rapid outflow of the water expelled through the pallial cavity, in which the anus of the animal opens.

In November of 1855, from the depths of the French Antilles, an animal was fished out an empty, strange shell which, fortunately, was spotted by the captain of the ship.

The Captain Beau, passionate about malacology, at once understood himself to be facing a very unique animal.

Unfortunately for him, however, little was known about fossil species and he had not realized that he had found the first current representative of an ancient family.

The Captain sent the specimen to the museum in Paris, where P. Fischer and A. Bernardi, two famous scientists, immediately understood to have in the hands the first actual specimen of a Pleurotomaria: a true “living fossil”!

The following year, in 1856, the two scientists published the startling discovery, sparking a revolution in the scientific world, showing, however, very little sensitivity ...

... in fact, instead of naming the new species to its discoverer, the two scientists dedicated it to their colleague Jan René Quoy, calling it Pleurotomaria quoyana. Captain Beau was offended and demanded to immediately have his shell returned.

The specimen of Beau had been caught dead and so it was not at all certain that the species was still alive: there was no absolute certainty.

The certainty came only in 1879, when from the depths off Barbados, the malacologist William Dell fished the first living specimen of what is nowknown as Perotrochus quoyanus.

It also turned out that Commander Beau was not the first!
While the Beau shell marked the official rediscovery of the Pleurotomarie for science, it was not the first ever find

In fact, in 1843 the Japanese scientist Sekjiu Musashi, in his monumental volume "Illustration of shells", had already depicted a living specimen of this family.

 The total closure to the West at that time was in force in Japan, meaning that the discovery remained confined to the Celestial Empire.

Musashi did not establish a real scientific name for his Pleurotomaria, but limited himself to dedicating it to the Celestial Emperor with the simple name of "Mikado", a title for the emperor.

In a hundred-year tradition, the Japanese Imperial Family had seen great specialists and shell collectors.

Among these, Emperor Hirohito was undoubtedly the most famous, but under the reign of his father Yoshihito, the Mikado had become the symbol of the imperial shell.

Anyone caught with one of these shells was obliged to give it to the Emperor - otherwise, it was said, he would have risked losing his head.

Despite all this, the adventure is just beginning...

To date (January 2018) we know only 35 living species, for some of which the validity is still uncertain and five of these have been discovered and described only between 2015 and 2017.

All are confined in very deep waters (often over 500 m),
and some of them are known only for very few specimens ...

... but the research of these ancient shells must be considered only at the beginning.

To date there is no evidence that any museum in the world has all known species; in the Museo Malakos collections  23 species can be admired.
Credits: Story

Enrico milanesi Ph

Comune di Città di Castello

Credits: All media
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