Complex sentence: The spirally coiled shells (and spirally coiled visceral mass) of most shelled gastropods clearly show either right-handedness or left-handedness, although there are a few confusing exceptions that can be hard to interpret.
Split into simpler sentences: The spirally coiled shells (and spirally coiled visceral mass) of most shelled gastropods clearly show either right-handedness or left-handedness. There are however a few confusing exceptions that can be hard to interpret.