A new, large species of Gomphonema Ehrenberg from ancient Lake Matano, Indonesia

A large species of the diatom genus Gomphonema Ehrenberg, G. matanensis sp. nov., is described as new to science from ancient Lake Matano, Indonesia. Light and scanning electron microscopic observations of the valve morphology of this species are presented. The morphology of this species is similar to other large species that have ovoid areolar openings without external flaps or occlusions, such as G. gomphopleuroides Amosse ex Kociolek, Glushchenko & Kulikovskiy and members of the G. kaznakowi species complex, both known from Southeast Asia. This species has the special features of bi- and triradiate siliceous growths at the valve mantle junction, continuing onto the mantle. Though an analysis of the phylogenetic relationships of the diatom genus Gomphonema is currently wanting, it would appear that gigantism occurred several times within the genus.