Surviving the marine environment: two new species of Mallomonas (Synurophyceae)

The genus Mallomonas consists of single-celled flagellates covered with siliceous scales and bristles and is well known in freshwater environments. Two new marine Mallomonas species were collected from Dongho Beach, Jeollabukdo, Korea. To fully understand the taxonomy of the new species, we performed molecular phylogenetic analysis based on a concatenated dataset and observed morphological features using light and electron microscopy. For the phylogenetic analysis, we used a combined dataset from five gene sequences: nuclear small subunit (SSU) and large subunit (LSU) rDNA and plastid LSU rDNA, rbcL and psaA genes. The new species M. cuspis sp. nov. grouped with M. heterospina and M. oviformis in the section Planae. It had scales with a broad shield marked with V-shaped internal ridge that lacked submarginal ribs and a dome. The other new species, M. marina sp. nov., clustered with M. cratis, M. pseudocratis, M. asmundiae and M. striata var. serrata in section Striatae and had scale characters that matched the group, including a well-developed posterior submarginal rib and series of transverse ribs on the shield and dome. In addition, we investigated the effect of salinity on growth rate and cell morphology. The two marine species represented high growth rate between salinities of 10 and 30 psu, suggesting that both species are well adapted in marine environments. When exposed to salinities of 0 and 5 psu, they underwent cell enlargement.