Rapheless valve

The valve of a monoraphid pennate diatom lacking a raphe.

Alternative Terms

pseudoraphe valve
The term pseudoraphe is used in much of the literature, including in Patrick and Reimer (1966).
The abbreviation for pseudoraphe valve, PRV, is used by Kingston in Wehr and Sheath (2003).
central sternum
The pseudoraphe is called the "central sternum" by some authors.
P Curtissimum Rapheless
Image Credit: Marina Potapova
Psammothidium curtissimum is a monoraphid diatom. Here, the rapheless valve and raphe valve of a single frustule are shown together.
N Lapidosa
Image Credit: Marina Potapova
Many species of Nupela are monoraphid and are commonly confused with other genera, including Achnanthidium. The rapheless valve of N. lapidosa is shown in LM.