Monterey Bay Aquarium Research Institute
Marine Botany

Pseudo-nitzschia Valve Structure

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Valves in Pseudo-nitzschia

A complete frustule of Pseudo-nitzschia includes an epitheca and hypotheca. The epitheca is the older and larger component of the diatom, including both the epivalve and the epicingulum (Figure 1). The hypotheca, on the other hand, is the younger and smaller portion of the organism, and it includes both the hypovalve and the hypocingulum. The girdle is composed of the epicingulum and hypocingulum.

Valve Markings

Pseudo-nitzschia is a pennate diatom and thus is characterized by valve markings that are separated by a median line. The valves of the frustule are composed of silica ribs formed from the silica deposition vesicles (SDV).These silica ribs grow in an elongated pattern rather than the circular pattern of centric diatoms and are used in order to characterize Pseudo-nitzschia along with other pennate diatoms. Along with the pattern of silica ribs, there are pores that are present within the valves that are also useful for taxonomical purposes.

Don't Forget!

Definitions and more information about valve structure and formation can be found in the General Information and Silicon Use sections of this web page.


Components of the Frustule

Complete frustule:

visualized as both an epitheca (purple) and a hypotheca (pink), in cross-section






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copyright Jennifer Shin 1999.

Last updated: Feb. 05, 2009