Pervalvar axis

The axis of the valve which is perpendicular to the center of the valve face. In centric diatoms, the center is the meeting point of the radii. In pennate diatoms, the center is the meeting point of the apical and transapical axes.

Pervalvar
Image Credit: Marina Potapova
The pervalvar axis of Stephanodiscus yellowstonensis is indicated by the black line.