Coolia Meunier is an important component of benthic dinoflagellate assemblages in tropical and subtropical seas. In this study, detailed morphological observation of Coolia species from Malaysian waters was carried out using light and electron microscopy in parallel with molecular characterization of nuclearencoded partial LSU rDNA, and internal transcribed spacer (ITS) regions. Live specimens were collected from seaweed samples and established into clonal cultures. There are significant morphological variations between the Malaysian isolates in comparison to the type species, C. monotis Meunier. The feature that differentiates the new species is the third postcingular plate (3¢¢¢), which is the largest hypothecal plate in the Malaysian isolates, whereas in C. monotis, the 3¢¢¢ and 4¢¢¢ plates are almost equal in size. Detailed observations of the thecal pores also revealed the presence of fine perforations within the pores of the Malaysian isolates, but these perforations are absent in C. monotis. Comparisons between Malaysian isolates and C. monotis nucleotide sequence of the ITS region showed high genetic divergence at 28%, in contrast to the 0.3%-3% divergence observed among populations of the same species. Structural comparison of the second internal transcribed spacer (ITS2) rRNA transcript between the two species showed compensatory base changes (CBCs) in the three helices of ITS2 rRNA. Based on morphological and molecular data, the Malaysian isolates are considered to represent a new species, for which the name Coolia malayensis is proposed.

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Field sampling was undertaken to investigate the occurrence of Pseudo-nitzschia Peragallo species in eight locations along the coast of Malaysian Borneo. A total of 108 strains of Pseudo-nitzschia species were isolated, and their morphology examined with SEM and TEM. Additionally, molecular data from nuclear-encoded partial LSU rDNA, and ITS regions, were characterized. A total of five species were confidently identified based on a combination of distinct morphological characteristics and supporting molecular evidence: P. brasiliana Lundholm, Hasle & Fryxell, P. cuspidata (Hasle) Hasle, P. dolorosa Lundholm & Moestrup, P. micropora Priisholm, Moestrup & Lundholm, and P. pungens (Grunow) Hasle var. pungens. However, one morphotype from Sarawak, while somewhat similar to P. caciantha, showed significant morphological distinction from this and any other of the currently described species. Most notably this morphotype possessed a characteristic pore arrangement in the poroids, with the fine pores in each perforation sector arranged in circles. Pair-wise sequence comparison of the LSU rDNA between this unidentified morphotype and P. caciantha Lundholm, Moestrup & Hasle, revealed 2.7% genetic divergence. Phylogenetic analyses strongly supported the monophyly of the morphotype. Based upon these supporting data it is here described as a new species, Pseudo-nitzschia circumpora sp. nov. A key to the six species of Pseudo-nitzschia from Malaysian Borneo is presented. Molecular signatures for all species were established based on structural comparisons of ITS2 rRNA transcripts.

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