Craticula
Craticula is a term applied to internal valves that are formed by species in the genus Craticula. Frustules that are normal in morphology produce the craticular stage under conditions of high solute concentration. The craticular valves consist of a raphe-sternum and robust transverse bars. These internal valves are formed within normal valves and, unlike normal valves, their formation is not linked to mitosis.
Image Credit: Sarah Spaulding
High level of focus showing parallel striae of the normal valve.
Image Credit: Sarah Spaulding
Mid level of focus showing the robust transverse bars of the internal craticula stage.
Image Credit: Sarah Spaulding
Deep level of focus showing both the craticula and the radiate striae of the heribaudii stage.