How snails breathe through snorkels on land

Microscope work may have solved the puzzle of Asian snails’ “useless” snorkels.

The small Alycaeidae land snails of Asia grow what looks like a tiny breathing tube curling partway along the outside of their shells. Similar tubes let some other land snails breathe when a little blast-door operculum shuts the main opening of their shells. But in the 350 or so Asian species of Alycaeidae, the supposed breathing tube’s outside end is sealed.

Researchers decades ago wondered if the tube had teensy pores or if it broke open in the wild. The answer is neither, Barna Páll-Gergely of Shinshu University in Matsumoto, Japan, and colleagues report July 12 in Biology Letters. Electron microscope images now reveal tiny feeder channels branching down from the tube to the bottom whorl of the shell, opening in vanishingly small slits to outside air.

The Alycaeus conformis snail’s roughly 50 air channels each squeeze down to about 16 micrometers in diameter, far too small for parasites such as slug mites to invade, Páll-Gergely says. These microchannels with slits might minimize water loss during hot weather. Alycaeidae snails, he says,  have evolved the “most complex gas-exchange system” yet discovered among snail snorkels.