it is not easy to see the nucleus of a Spirogyra. In most cases it is hidden by the chloroplast, especially when it is narrow screwed. In the one shown here the chloroplast made wide windings and thus in the middle of the cell the nucleus is visible, even in this normal bright-field shot.
Yes the nucleus is well hidden in this algae. I have attempted many times to locate and photograph the nucleus of Spirogyra but have only succeeded once. 