You need to have pretty good eyesight to see the tiny snails from the genus Plectostoma. These almost impossibly small gastropods from Malaysia and Thailand only reach a millimeter or two in width, but they make up for their lack of size with their stunning beauty. The 31 Plectostoma species described in a new paper published this week in ZooKeys all feature shells that twist and whorl into amazing, complex shapes. Their shells are also so thin that they practically glow in the sunlight. The snails—10 of which are new to science and many of which are endangered—have been called "microjewels" by Dutch Ph.D. student Thor-Seng Liew for their ornate coils and ornamentations.
Unfortunately, these tiny snails live in very small microhabitats which are quickly disappearing. As Liew and his co-authors describe in the paper, the snails live only on limestone hills, which are not only relatively rare in Southeast Asia but have also been actively mined as a source of raw materials for concrete. Most of these species have habitats limited to individual limestone hills, making them particularly vulnerable to habitat loss and extinction.
In fact, the paper reports that one species, P. sciaphilum, which was first discovered in 1952, is now extinct. Its only habitat was quarried away in 2003. The authors warn that another species, P. tenggekensis, described by science for this first time in this paper, also faces the threat of ongoing quarrying and might not last until the end of this year.
All told, six of the 31 species described in the paper are critically endangered. One is endangered, while the authors warn that three more should be considered vulnerable to extinction. (These assessments have not yet been added to the IUCN Red List of Threatened Species.)
The 107-page paper describing these snails is itself pretty amazing. It elevates the previously known snails from what had earlier been described as a subgenus, Opisthostoma, to the full genus of Plectostoma. The taxonomies of the 21 species that had previously been described have all been revised and the 10 new species have full descriptions, complete with 3D models of their shells developed through computerized X-ray tomography (better known as CT scans) and DNA barcodes for each species.
By the way, this is the first of two papers on these microjewels. A second, as yet unscheduled, will describe another batch of Plectostoma species living in Sumatra. I guess it takes a massive amount of research to describe even the tiniest of species.
Photographs by Thor-Seng Liew. Used under Creative Commons license