en Ecology Ecology پژوهشي Orginal research papers <span style="line-height: 115% font-family: "Times New Roman","serif" font-size: 12pt mso-bidi-language: AR-SA mso-fareast-font-family: Calibri mso-ansi-language: EN-US mso-fareast-language: EN-US">Phytoplankton cells and resting cysts of the species <i style="mso-bidi-font-style: normal">Scrippsiella</i> <i>trochoidea</i> are regular and dominant components of the dinoflagellate flora of coastal marine waters and sediments around the world. This species is a common harmful bloom forming species in coastal waters. In this study, for the first time cyst of S<i>. trochoidea</i> were<i> </i>isolated from the sediments of southeast coast of<font size="3"><font face="Times New Roman"><span style="color: red"> </span>Iran. Five strains from the germination of a single cyst belonged to<i> S. trochoidea</i>. In order to confirm identification of the species an excystment and encystment experiment, cyst and germinated cell morphology and plate pattern by light and electron microscopy (SEM) have been described. The nucleotide sequences of two highly diverse regions, the rDNA-ITS 1,2 and 5.8S-rDNA have been sequenced for all strains. Homologous sequences from GenBank with five Iranian strains were compared to find their phylogenetic relationship. Both NJ and MP phylogenetic and morphological analysis showed five strains of <i>S. trochoidea</i> from Iran were clustered with previously described <i>S. trochoidea</i> and <i>Calciodinellum levantinum</i> species, and its closest relationship was with <i>Scrippsiella </i>sp. strain with a 1.2-1.4% sequence divergence.<span style="mso-spacerun: yes"> </span>Results indicate that molecular studies of rDNA if combined with morphological cyst and vegetative cells could be a valuable approach to identification and taxonomy of calciodinelloideae dinoflagellate.</font></font></span> Cyst, Iran south coast, Molecular analysis, Morphology, Phylogeny, Scrippsiella trochoidea, Sediment, Vegetative cell 252 270 http://jifro.ir/browse.php?a_code=A-10-1-153&slc_lang=en&sid=1 G. Attaran-Fariman G.Attaran@cmu.ac.ir 10031947532846003182 10031947532846003182 Yes C. J. S. Bolch 10031947532846003183 10031947532846003183 No