About Physella johnsoni (Clench, 1926)
Physella johnsoni is an aquatic pulmonate gastropod mollusk, commonly called the Banff Springs snail. Individuals are roughly the size of unpopped corn kernels; the largest specimens reach only about one centimeter in length. Like all members of the Physidae family, this species has sinistral, or left-handed coiled, shells. The snail feeds on periphyton. It was first formally identified in 1926 from the nine sulphurous hot springs located on Sulphur Mountain in Banff National Park, Alberta, Canada, and is found nowhere else in the world. This snail is highly unusual for its adaptation to life in thermal springs, where the water has low oxygen levels and high hydrogen sulfide content — an environment too harsh for most animals to survive. Since its initial discovery, the species' range has contracted, and it now only occurs in five of the original nine hot springs.
