From Lundholm et al. 2012
The cells are lanceolate in girdle view, and in valve view they are lanceolate in longer specimens, tending towards being more rhomboid in smaller specimens. The valve ends are broadly pointed. They are 40–54 μm long and 2.1–2.5 μm wide. The fibulae are not always regularly spaced. The two central fibulae have a larger interspace and the raphe is here interrupted by a central nodule. The densities of fibulae and interstriae are 18–25 and 34–40 in 10 μm, respectively. The striae contain one row of rounded to squared poroids that are more or less confluent, 5–6 (sometimes 7) poroids in 1 μm. Each poroid most often contains 1–3 sectors, but sometimes 4 sectors are seen. In addition, some striae are simply composed of more lightly silicified areas without any perforations. The exact number of sectors may often be difficult to discern as the striae are lightly silicified. The sections are often of varying size and the perforations within them are arranged in a hexagonal pattern. The mantle is often 1–2 poroids high and has composition similar to the valve. The girdle comprises 3–4 bands. The valvocopula contains one longitudinal row of 41–50 band striae in 10 μm. The structure of the striae on the valvocopula is variable, even within the same band, varying from being 2 poroids wide and 1–3 poroids high to being irregularly divided into two or more parts. In the second and the third band, the band striae are split in a decreasing number of parts and both bands have an abvalvar part that is either without perforations or contains few transverse slit perforations. The fourth band is not perforated and has a more silicified line in the middle. The bands are of decreasing width in abvalvar direction.
Pseudo-nitzschia fryxelliana has been reported from Kalaloch Beach and Teawhit Head, Washington State, USA (Lundholm et al. 2012).
Pseudo-nitzschia fryxelliana is a pennate diatom found in marine waters. It has not been tested for domoic acid production.
Pseudo-nitzschia fryzelliana is a part of the P. pseudodelicatissima complex. It looks most like P. calliantha, P. mannii and P. caciantha, but differes from them in having a lower fibula density (Lundholm et al. 2012).
From Lundholm et al. 2012
Synapomorphy in helix IV of ITS2 of the nuclear rDNA: 5′-CTAAGTCTGGCTTGCAGTGGTGAACATTAGTTTATCACCTGCTCG-3′ (45 bp). This sequence includes CBCs and HCBCs, differentiating it from the morphologically most similar species P. mannii, P. calliantha, and P. hasleana. A test for the uniqueness of the diagnostic signature of P. fryxelliana is, was confirmatory. In GenBank, the next closest hits had E-values of 2.9 and were all mammals.
