Pseudo-nitzschia cuspidata (Hasle) Hasle emend. Lundholm, Moestrup & Hasle
Pseudo-nitzschia cuspidata is a domoic-acid-producing, pennate diatom (Bill et al. 2005, Trainer et al. 2009) found in tropical and temperate waters. It has been reported as a major bloom-former in the Juan de Fuca eddy (Trainer et al. 2009).
P. cuspidata is part of the P. pseudodelicatissima group. Cells are long and thin and form the step-chains characteristic of the genus. Poroids are round to square and have a hymen with two large perforations, one at the top and one at the bottom.
From Lundholm et al. 2003: Overlapping cells in colonies. Cells lanceolate in valve view, tapering from the middle toward the tips. Transapical axis of valves 1.4-2.0 microns, apical axis 30-72 microns. Eccentric raphe divided by a central nodule. The fibulae regularly spaced, 19-25 in 10 microns, interstriae 35-44 in 10 microns. Striae with one row of oval to square poroids, 4-6 poroids in 1 micron. Hymen of poroids divided into two perforated parts. Valve mantle structured as valve face, one poroid high. Cingulum with open bands, containing one row of 47-53 poroids in 10 microns. Each poroid may be partly split.
Can be difficult to differentiate from P. pseudodelicatissima. Use the valve width, density of striae, density of fibulae, poroid hymen, structure of band striae and density of band striae to identify (Lundholm et al. 2003).
A maximum likelihood tree based on ITS rDNA shows that P. cuspidata is most closely related to P. pseudodelicatissima (Lundholm et al. 2003).
Pseudo-nitzschia cuspidata is found in tropical and temperate coastal waters. It has been documented in the Chesapeake Bay (Marshall et al. 2005). See Lundholm et al. (2003) for a list of P. cuspidata reports.