REPRODUCTION AND LIFE HISTORY OF THE RED ALGA GALAXAURA OBLONGATA (NEMALIALES,GALAXAURACEAE)1

Culture and morphological studies showed that Galaxaura oblongata (Ellis et Solander) Lamouroux has a triphasic life history with conspicuous gametophytes and small filamentous tetrasporophytes. Development of male and female reproductive structures is very similar and both begin with the enlargement of a terminal cell of a filament branch occupying a normal vegetative position within the apical pit of a thallus branch. In male thalli this modified branch forms a conceptacle in which spermatangia are produced. In female thalli, this modified branch forms a three-celled carpogonial branch consisting of a carpogonium, hypogynous cell and basal cell. Filament branches from the basal cell form a pericarp and the gonimoblast develops directly from the carpogonium. Carposporangia are produced in conceptacles which resemble the male conceptacles. About the time the first carposporangia are produced, the carpogonium, hypogynous cell and basal cell form a large fusion cell. Released carpospores germinate in a unipolar or bipolar manner and form small filamentous thalli. Under short day conditions, cruciate tetrasporangia are produced in small clusters. Tetraspores germinate similarly to carpospores and also form small filamentous thalli. Under low nutrient conditions, small cylindrical thalli develop on the filaments and these appear similar to gametophytes collected in nature.