Diatoms of North AmericaDiatoms of North America

Glossary

Like the rest of this website, the glossary is a work in progress. If we’ve missed a term, please contact us to let us know the term and references.

Terminal raphe fissure

A terminal raphe fissure is an external extension of the distal the end of the raphe, beyond the helictoglossa. The fissure does not penetrate the valve wall. Instead, the fissure is open externally, but not internally.

The presence and the structure of the terminal raphe fissure is an important taxonomic feature. Many genera possess a terminal raphe fissure, including biraphid genera (Navicula, Cymbella, Encyonema, Fallacia) and monoraphid genera (Planothidium).

Citations

Terminal Raphe Fissure
Image Credit: Marina Potapova
Scanning electron micrograph of external view of the terminal raphe fissure of Planothidium delicatum.
No Terminal Raphe Fissure2
Image Credit: Marina Potapova
External view of Achnanthidium kriegeri, which lacks a terminal raphe fissure.
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