Polar bar

A hyaline thickening of silica at the valve apices in some pennate species. The genus Sellaphora possesses variable development of polar bars.

Alternative Terms

transapical thickening
Some authors use "transapical thickening", rather than polar bar.
Polar Bar1 Copy
Image Credit: Marina Potapova
Scanning electron micrograph of Sellaphora wallacei showing the polar bar at the apex.
Holo2B Rexii
Image Credit: Marina Potapova
Light micrograph of Sellaphora rexii, with the thickening of the polar bar appearing lighter than other parts of the valve.