Morphology and phylogeny of Scrippsiella trochoidea (Dinophyceae) a potentially harmful bloom forming species isolated from the sediments of Iran’s south coast

Phytoplankton cells and resting cysts of the species Scrippsiella trochoidea 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. trochoidea were isolated from the sediments of southeast coast of Iran. Five strains from the germination of a single cyst belonged to S. trochoidea. 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 S. trochoidea from Iran were clustered with previously described S. trochoidea and Calciodinellum levantinum species, and its closest relationship was with Scrippsiella sp. strain with a 1.2-1.4% sequence divergence. 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