Endosymbiotic diatoms from previously unsampled habitats

New endosymbiotic diatom isolations from previously unsampled field sites are reported. Nitzschia laevis was the most commonly isolated diatom from populations of Amphistegina lobifera collected at both the North Beach in the Gulf of Eilat and at Sifnos, Greece. Nitzschia frustulum var. symbiotica (as emended by Lee et al., 2000) was the second most abundant species of diatoms found in the Amphistegina examined from the North Beach, Gulf of Eilat, (31%) and Sifnos, Greece, (28%) and the most abundant diatom species present in the specimens examined from Coconut Beach, Lizard Island, Great Barrier Reef. New observations are not entirely in consonance with previous observations, but one general conclusion has not changed: a small number of diatom species (~20) are involved in the endosymbiotic phenomenon and certain species are dominant in every population. A rare, yet to be described, nitzschioid diatom was found and figured.