en Ecology Ecology پژوهشي Orginal research papers <span style="FONT-FAMILY: "Times New Roman","serif" FONT-SIZE: 12pt mso-bidi-font-size: 14.0pt mso-fareast-font-family: 'Times New Roman' mso-bidi-font-family: 'B Zar' mso-bidi-language: AR-SA mso-ansi-language: EN-US mso-fareast-language: EN-US">Resting cyst and motile thecate cell stages of three heterotrophic <i>Protoperidinium oblongum</i>,<b><i> </i></b><i>Protoperidinium<b> </b></i>sp<b><i> </i></b>and <i>Protoperidinium claudicans</i> were assessed. Cysts were isolated from sediment collected from southeast coast of Iran. Individual live cysts were incubated under optimal conditions for germination. Results showed that <i>Protoperidinium oblongum</i> cysts were pentagonal smooth walled and three cysts of this species were identified from Iranian sediment. The germinated cell of <i>P. oblongum</i> was colourless and elongated pentagonal in shape.<font size="3"><font face="Times New Roman"><span style="mso-spacerun: yes">  </span><i>P. claudican</i> theca cell has a pointed antapical horn with a four sided apical plate. <i>Protoperidinium<b> </b></i>sp. had dark brown pentagonal cyst. Its germinated cell differed from other <i>Protoperidinium</i> species. Two divergent distally antapical horns formed 90˚ between the horn and Posterio-lateral of main body edge, thus, comprising a unique species in the <i>Protoperidinium</i> genus. This kind of antapical horn has not been previously reported among <i>Protoperidinium</i> spp.</font></font></span> Phytoplankton, Protoperidinium, Taxonomy, Cyst, Germinated cell, Sediment, Chabahar bay, Iran 1 12 http://jifro.ir/browse.php?a_code=A-10-1-55&slc_lang=en&sid=1 G. Attaran-Fariman gilan.Attaran@gmail.com 10031947532846001060 10031947532846001060 Yes S. Khodami 10031947532846001061 10031947532846001061 No C. J. S. Bolch 10031947532846001062 10031947532846001062 No