of calcium.caroonare pecipiiateu iu nature of coiled shells, gastropods possess a quality known as chirality or "handedness." Over_ 90% of gastropods have a dextral or "righthand shell. Left-hand coiled shells are referred to as sinistral. If the opening (aperture) of a shell is on the right side when the shell is held with spire pointing upwards, the shell is said to be dextral. Occasionally, dextral species will produce sinistral shells, and vice-versa. These oddities are highly sought after by shell collectors. cnGcies of arboreal (treedwelling) land snails that show normally mixed coiling.