Morphological observation of two species of Pseudo-nitzschia (Bacillariophyceae)

About one third of the species in the genus Pseudo-nitzschia has been known to produce domoic acid, which is responsible for amnesic shellfish poisoning, resulting in human intoxication and the death of marine fauna. Precise identification to species level was done based on ultrastructure of frustules marking, which includes fibulae, striae, poroids and central interspace, as well as the cell dimensions. In this study, detail morphological observation of field samples and clonal cultures of Pseudo-nitzschia from estuarine waters in Kuching, Samariang Batu, Santubong and Muara Tebas was carried out using electron microscopy (SEM and TEM). Diatom cells were treated with acid to remove organic cellular contents before observation under SEM and TEM. Two morphotypes were observed from these three locations. One morphotype possesses a rectangular valve shape, the apical and transapical axis of 31.9-36.8μm and 2.6-3.0μm, respectively, with 21-25 fibulae and 21-24 striae in 10μm. The other morphotype shows linear to lanceolate cell shape with the apical axis of 67.2-79.9μm and the transapical axis of 3.0-3.5μm. Numbers of fibulae and striae in 10μm are 12-13 and 11-14, respectively. Central interspace is absent in both morphotypes. Based on the ultrastructure, the two morphotypes of Pseudo-nitzschia is designated as P. brasiliana and P. pungens, respectively.Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalga