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

A term that applies to some concentrically undulate Stephanodiscus species. In these taxa, central fultoportulae are present on both the concave and the convex valve of the diatom frustule. From Greek for “same place”.

See also 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).