MORPHOLOGY AND MOLECULAR CHARACTERIZATION OF PSEUDO-NITZSCHIA (BACILLARIOPHYCEAE) FROM MALAYSIAN BORNEO, INCLUDING THE NEW SPECIES PSEUDO-NITZSCHIA CIRCUMPORA SP. NOV 1 Hong-Chang Lim Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, 94300, Malaysia Chui-Pin Leaw Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, 94300, Malaysia Suriyanti Nyun-Pau Su Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, 94300, Malaysia Sing-Tung Teng Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, 94300, Malaysia Gires Usup Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, 43600, Malaysia Normawaty Mohammad-Noor Kulliyyah of Science, International Islamic University Malaysia, Bandar Indera Mahkota, Kuantan, Pahang, 25200, Malaysia Nina Lundholm Natural History Museum of Denmark, University of Copenhagen, Sølvgade 83S, Copenhagen, 1307, Denmark Yuichi Kotaki School of Marine Biosciences, Kitasato University, Kitasato 1-15-1, Minami-ku, Sagamihara, Kanagawa, 252-0373, Japan and Po-Teen Lim 2 Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan, Sarawak, 94300, Malaysia 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 molec- ular 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. Key index words: Malaysia; molecular signature; mor- phology; Pseudo-nitzschia circumpora; Pseudo-nitzschia In Malaysia, the most prominent HAB- related human toxic syndrome is paralytic shellfish poisoning (PSP), which has resulted in several fatali- ties (Usup et al. 2002, Lim et al. 2004). Intensive monitoring of PSP toxin-producing dinoflagellates 1 Received 20 July 2011. Accepted 30 April 2012. 2 Author for correspondence: e-mails ptlim@frst.unimas.my, poteenlim@gmail.com. J. Phycol. 48, 1232–1247 (2012) © 2012 Phycological Society of America DOI: 10.1111/j.1529-8817.2012.01213.x 1232