Snails Differentiated

How to Tell the Banff Springs Snail from Other Snails

The Banff Springs Snail can easily be distinguished from other freshwater snails by examining its shell and where it lives. The Banff Springs Snail belongs to the Family Physidae. All species within Physidae have shells that coil to the left (sinistrally). All other families of freshwater snails in North America with a cone-shaped shell have shells that coil to the right (dextrally). By holding the shell with the aperture (the hole from which the snail’s body pokes out) towards you and the apex (tip) of the shell upwards, sinistrally coiling shells will have the aperture on the left.

Sinistral (left shell = Banff Springs Snail) and dextral (right shell = Pond Stagnicola) snail shells. The Banff Springs Snail shell is from Lower Middle Spring while the Pond Stagnicola is from the Vermilion Lakes wetland.

Sinistral (left shell = Banff Springs Snail) and dextral (right shell = Pond Stagnicola) snail shells. The Banff Springs Snail shell is from Lower Middle Spring while the Pond Stagnicola is from the Vermilion Lakes wetland.

In the thermal springs where they live, we have seen Banff Spring Snails that are light brown in colour as well as those that are nearly black. Many have a white coating on their shells which could be bacterial and algal growth or minerals deposited from the thermal spring water.

The shell of the Banff Springs Snail is shaped like a lemon seed and is about the same size as a lemon or orange seed or an un-popped kernel of popcorn. When baby snails hatch from their egg, they have a shell 0.8 mm long – about the size of the period at the end of the sentence. Most of the adult snails have shells around 5 mm but large individuals, with shells up to 11 mm long, are commonly found in the Basin Spring pool.

Banff Spring Snails have two long, thin tentacles on their head. At the base of each tentacle is a small black eye. Their foot is shaped like a tear-drop. When they are upside down, suspended on the water’s surface tension, you might be able to see waves of muscle contractions run down the foot – that’s how they move over rocks, sticks, or on the water’s surface – gliding along a path of clear mucus.

Scientists have studied the allozymes and mitochondrial DNA of Banff Spring Snails and have concluded that it is indeed a unique species, separate from all others in the world.

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Close-up of a Banff Springs Snail (Physella johnsoni), through a microscope. The black eyes can be seen at the base of the long, thin tentacles.

Next Page – How did the Banff Springs Snail Evolve?