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Two new marine unicellular red algae are described: Timspurckia oligopyrenoides gen. et sp. nov. isolated from southeastern Australia and Erythrolobus madagascarensis sp. nov. isolated from Madagascar. Timspurckia oligopyrenoides cells are spherical, 7-11 μm in diameter, greyish red to reddish brown and surrounded by a conspicuous fibrillar matrix about 2 μm thick. Cells exhibit positive phototaxis. In the single chloroplast the lobes extend from several pyrenoids to occupy most of the cell. A peripheral thylakoid is absent. The pyrenoid matrices are filled with tubular thylakoids and are usually surrounded by starch sheaths in the adjacent cytoplasm. The nucleus is peripheral with a nucleolus appressed to the nuclear envelope usually closest to the cell center. Golgi bodies are associated with mitochondria usually at the cell periphery. Erythrolobus madagascarensis cells are spherical, 5-8 μm in diameter, greyish red to reddish brown and surrounded by a thin conspicuous fibrillar sheath. Cells exhibit positive phototaxis. Each cell has a single chloroplast with several lobes extending from an eccentric pyrenoid forming a complex parietal layer. A peripheral thylakoid is absent. The pyrenoid matrix is filled with tubular thylakoids, and a starch sheath is visible in the adjacent cytoplasm. The nucleus is eccentric and has a central nucleolus. Golgi bodies are associated with mitochondria usually at the cell periphery. Numerous conspicuous, electron-transparent, fibrous vesicles are always present in the cells. The sequence divergences of psaA and psbA genes and phylogeny support that E. madagascarensis sp. nov. and T. oligopyrenoides gen. et sp. nov. are newly uncovered natural entities within the class Porphyridiophyceae along with Erythrolobus coxiae, Porphyridium spp. and Flintiella sanguinaria. The low-molecular-weight carbohydrates (LMWCs) floridoside, digeneaside and trehalose are present in both taxa. Thus, three independent features - ultrastructural characters, plastid gene sequences and LMWC patterns - support the suggested phylogeny and taxonomy of these red algae. [ABSTRACT FROM AUTHOR]