WoRMS taxon details
Pseudo-nitzschia obtusa (Hasle) Hasle & Lundholm, 2005
531455 (urn:lsid:marinespecies.org:taxname:531455)
accepted
Species
marine, terrestrial
recent only
(of Nitzschia seriata f. obtusa Hasle, 1965) Hasle, G.R. (1965). Nitzschia and Fragilariopsis species studied in the light and electron microscope. II. The group Pseudonitzschia. Skrifter utgitt av Det Norske Videnskaps-Akademi i Oslo, Matematisk-naturvidenskapelig klasse, Ny Ser.,, 18: 45 pp., 17 pls
page(s): p. 10; pl. 3, fig. 8, 9, 11, pl. 4, fig. 5-7 [details]
(of Nitzschia seriata f. obtusa Hasle, 1965) Hasle, G.R. (1974). Validation of the names of some marine planktonic species of Nitzschia (Bacillariophyceae). Taxon, 23(2/3): 425-428, available online at https://doi.org/10.2307/1218752
page(s): p. 427 [details]
page(s): p. 10; pl. 3, fig. 8, 9, 11, pl. 4, fig. 5-7 [details]
(of Nitzschia seriata f. obtusa Hasle, 1965) Hasle, G.R. (1974). Validation of the names of some marine planktonic species of Nitzschia (Bacillariophyceae). Taxon, 23(2/3): 425-428, available online at https://doi.org/10.2307/1218752
page(s): p. 427 [details]
Distribution A cold-water species, so far restricted to the Northern hemisphere
Distribution A cold-water species, so far restricted to the Northern hemisphere [details]
Kociolek, J.P.; Blanco, S.; Coste, M.; Ector, L.; Liu, Y.; Karthick, B.; Kulikovskiy, M.; Lundholm, N.; Ludwig, T.; Potapova, M.; Rimet, F.; Sabbe, K.; Sala, S.; Sar, E.; Taylor, J.; Van de Vijver, B.; Wetzel, C.E.; Williams, D.M.; Witkowski, A.; Witkowski, J. (2026). DiatomBase. Pseudo-nitzschia obtusa (Hasle) Hasle & Lundholm, 2005. Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=531455 on 2026-10-06
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Nomenclature
original description
(of Nitzschia seriata f. obtusa Hasle, 1965) Hasle, G.R. (1965). Nitzschia and Fragilariopsis species studied in the light and electron microscope. II. The group Pseudonitzschia. Skrifter utgitt av Det Norske Videnskaps-Akademi i Oslo, Matematisk-naturvidenskapelig klasse, Ny Ser.,, 18: 45 pp., 17 pls
page(s): p. 10; pl. 3, fig. 8, 9, 11, pl. 4, fig. 5-7 [details]
original description (of Nitzschia seriata f. obtusa Hasle, 1965) Hasle, G.R. (1974). Validation of the names of some marine planktonic species of Nitzschia (Bacillariophyceae). Taxon, 23(2/3): 425-428, available online at https://doi.org/10.2307/1218752
page(s): p. 427 [details]
basis of record Fourtanier, E. & Kociolek, J. P. (compilers). (2011). Catalogue of Diatom Names. California Academy of Sciences, On-line Version. Updated 2011-09-19., available online at http://researcharchive.calacademy.org/research/diatoms/names/index.asp [details]
new combination reference Hasle, G. R.; Lundholm, N. (2005). Pseudo-nitzschia seriata f. obtusa (Bacillariophyceae) raised in rank based on morphological, phylogenetic and distributional data. <em>Phycologia.</em> 44(6): 608-619., available online at https://doi.org/10.2216/0031-8884(2005)44[608:psfobr]2.0.co;2
note: P. obtusa raised in rank from P. seriata f. obtusa. The taxon was originally described in Hasle (1965) and Hasle (1993) [details]
page(s): p. 10; pl. 3, fig. 8, 9, 11, pl. 4, fig. 5-7 [details]
original description (of Nitzschia seriata f. obtusa Hasle, 1965) Hasle, G.R. (1974). Validation of the names of some marine planktonic species of Nitzschia (Bacillariophyceae). Taxon, 23(2/3): 425-428, available online at https://doi.org/10.2307/1218752
page(s): p. 427 [details]
basis of record Fourtanier, E. & Kociolek, J. P. (compilers). (2011). Catalogue of Diatom Names. California Academy of Sciences, On-line Version. Updated 2011-09-19., available online at http://researcharchive.calacademy.org/research/diatoms/names/index.asp [details]
new combination reference Hasle, G. R.; Lundholm, N. (2005). Pseudo-nitzschia seriata f. obtusa (Bacillariophyceae) raised in rank based on morphological, phylogenetic and distributional data. <em>Phycologia.</em> 44(6): 608-619., available online at https://doi.org/10.2216/0031-8884(2005)44[608:psfobr]2.0.co;2
note: P. obtusa raised in rank from P. seriata f. obtusa. The taxon was originally described in Hasle (1965) and Hasle (1993) [details]
Present Present in aphia/obis/gbif/idigbio Inaccurate Introduced: alien Containing type locality
From regional or thematic species database
Distribution A cold-water species, so far restricted to the Northern hemisphere [details]Harmful effects and toxins The species has been shown to produce domoic acid (0.167-0.332 pg per cell) in cultures from Greenland. The production was triggered when exposed to grazing copepods, (Hardardottir et al. 2015) [details]
Identification requires electron microscopy.
The main characteristics of P. obtusa are the asymmetric valve and the 2 rows of poroids. P. obtusa is phylogenetically and morphologically closely related to P. seriata and P. australis, two other species with asymmetric valves. The main differences are the number of poroid rows in the striae, poroid density, and valve width.
P. obtusa: 2 rows - 6-8 poroids/µm - 2.9-5.0µm
P. seriata:: (2)-4 rows - 6-9 poroids/µm - 4.6-8.0µm
P. australis:: 2 rows - 4-5 poroids/µm - 6.5-8.0µm
Verified sequences of ITS rDNA (ITS1, 5.8S, ITS2) are:
P. obtusa (DQ062667); P. seriata (DQ062663); P. australis (DQ062661) [details]
Toxicology The species has been shown to produce domoic acid (0.167-0.332 pg per cell) in cultures from Greenland. The production was triggered when exposed to grazing copepods, (Hardardottir et al. 2015) [details]
