Collum

The narrow, hyaline area on the valve mantle in the genus Aulacoseira. A small furrow, or sulcus, separates the collum from the portion of the valve mantle with areolae. See also ringleiste.

A Alpigena Collum
Image Credit: Marina Potapova
In this light micrograph, each arrow shows the collum on two valves of a single frustule in A. alpigena.
A Humilis Collum
Image Credit: Marina Potapova
In this scanning electron micrograph, each arrow shows the collum on two valves within a single frustule in A. humilis.
A Nivalis Collum
Image Credit: Marina Potapova
A scanning electron micrograph of a single valve of A. nivalis, showing the collum.