Complex sentence: The shell is smaller than "Muricopsis octogonus", without spines, but boldly sculptured with broadly rounded axial folds, overridden by prominent sharply raised spiral cords.
Split into simpler sentences: The shell is smaller than "Muricopsis octogonus", and has no spines. It is however boldly sculptured with broadly-rounded axial folds, overridden by prominent sharply raised spiral cords.