Usually applied to centric diatoms, the interfasciular area is the unornamented, thicked rib of silica located between fascicles.
Fissure that joins the proximal raphe ends in some cymbelloid taxa. Instead of distinct termination of the proximal raphe ends, they are connected, internally by a fissure.
Valves that are symmetrical to the transapical axis are termed 'isopolar'. The poles of these valves are similar in shape and size.
An isotype is any duplicate of the holotype; it is always a specimen.