To characterize the newly isolated microalga, we investigated its cell ultrastructure. It should be noted that ultrastructural studies of H. pluvialis are generally more difficult in comparison to most of green microalgae, mainly due to the presence of tough cell walls complicating the chemical fixation, embedding and preparation of ultrathin sections [18]. Indeed, we found that the thick cell wall of BM1 was, like that of H. pluvialis aplanospores, extremely resistant to mechanical disruption and chemical agents and presented difficulties for electron microscopy. Nevertheless, both transmission (Figure 3a,c,d) and scanning (Figure 3b) electron micrographs of ―green‖ and ―red‖ BM1 cells were obtained.