Glossary terms starting with "i"

Interfascicle - costa

An unornamented, thicked rib of silica located between fascicles. Usually applied to centric diatoms.


A valve with poles, or apices, of the apical axis having the same size and shape. Isopolar valves are symmetrical to the transapical axis.

Isotopic position

Applies to some concentrically undulate species of Stephanodiscus (e.g., S. niagarae) where fultoportulae on the valve face are in the central area of both the concave and the convex valves. From Greek for “same place”.

See contrasting term, heterotopic position.



A specimen from the original collection of the holotype and of the same taxon. A type material recognized by the International Code of Nomenclature for algae, fungi and plants (ICN).