For the first time, morpho-anatomical characters that were congruent with DNA sequence data were used to characterize several genera in Hapalidiaceae —the major eco-engineers of Subarctic carbonate ecosystems. DNA sequencing of three genes (SSU, rbcL, ribulose-1, 5-bisphosphate carboxylase/ oxygenase large subunit gene and psbA, photosystem II D1 protein gene), along with patterns of cell …