Biologists have discovered a new record-holder for the illustrious title of world's tiniest snail. Members of the diminutive mollusk species Acmella nana are only about half a millimeter wide and between 0.60 and 0.79 millimeters in height.
For your enjoyment, here is an image of the snail's tiny shells displayed on the small print of the paper announcing their existence, published today in the open access journal ZooKeys.
The new species bested the previous record-holder for world's smallest snail, the 0.80-millimeter-long Chinese snail Angustopila dominikae, which was announced only a month ago in another ZooKeys study.
A. nana was discovered by a team of Dutch and Malaysian researchers in the Bornean province of Sabah, and is one of 48 new snail species described in the study. According to study co-author and evolutionary biologist Menno Schilthuizen of the Naturalis Biodiversity Center, the tiny snail species has probably evolved to be smaller and smaller in order to utilize microscale environments that its competitors can't access.
"Different snail species tend to divvy up their environment into niches that differ in their physical and chemical aspects rather than food type, which insects, for example, tend to do," Schilthuizen told me over email.
"For a snail this tiny, that probably means they can squeeze into food-containing crevices that are so small that other species cannot get into them," he said.
But Schilthuizen and his colleagues won't know the finer details for sure without further research. In fact, they only reason they know about the existence of A. nana in the first place is from examining its discarded shells.
"The methods we use to collect them are aimed at empty shells," Schilthuizen explained. "We place sieved soil in buckets of water and scoop off the flotsam, which includes thousands of empty shells, so we have never seen this particular species of Acmella alive."
The team can, however, make assumptions about the diet and behavior of the new species based on its nearest relatives. According to Schilthuizen, live Acmella snails have been observed in underground crevices and limestone caves, where they feed on microbial films that grow on the rock. It's reasonable to presume A. nana has found a similar spelunking niche.
Clearly, the title of most miniscule mollusk has been heating up as of late, so perhaps biologists will end up rooting out snails that are even tinier than A. nana...and thus, even cuter.