A shell may be spiraled clockwise or spiraled counter clockwise. Most are spiraled clockwise with a few spiraled counter clockwise. Shells displaced an infinite variety of colors, patterns and shapes. Torsion, which is a twisting of the body, is thought to be a separate evolutionary process from the spiraling of the shell. There is not a widely accepted reason for torsion to have taken place.
Some scientist believes it occurred in the larval stage.
Other think torsion is an adult adaptation. It is thought the changes in torsion may have to do with head protections and the utilization of the anterior water stream. This design would allow for the withdrawal of the developed head when the organism retracts.