General Introduction -- Oxygenic Photosynthetic Microorganisms in Extreme Environments -- Phototrophs at High and Low Light -- Effects of Ultraviolet Radiation on Cyanobacteria and their Protective Mechanisms -- The Hidden Life of Algae Underground -- Meromictic Lakes as Habitats for Protists -- Marine Phototrophs in the Twilight Zone -- Phototrophs in the Marine Environment -- Biology of the Chlorophyll D-Containing Cyanobacterium Acaryochloris Marina -- Phylogenetics, Molecular Biology and Ecological Impacts of a Group of Highly Unusual Protists -- Diatoms -- The Margin of the Sea -- Seaweeds on the Abrasion Platforms of the Intertidal Zone of Eastern Mediterranean Shores -- Status of Mangrove Ecosystem -- Intertidal Sandy Beaches as a Habitat Where Plastid Acquisition Processes are Ongoing -- Hydrochemical Key to the Genesis of Calcareous Nonlaminated and Laminated Cyanobacterial Microbialites -- Soil and Freshwater Micro-Algae as a Food Source for Invertebrates in Extreme Environments -- Phototrophs in Cold Environments -- Cold Tolerance in Cyanobacteria and Life in the Cryosphere -- Cyanobacteria in Antarctic Lake Environments -- Green Cryosestic Algae -- Psychrophilic Diatoms -- Algae at Extreme Low Temperatures -- Phototrophs in Hot Alkaline and Acidic Environments and Non-Thermal Acidic Habitats -- Cyanidiophyceae -- Diversity of the Cosmopolitan Thermophile Mastigocladus laminosus at Global, Regional and Local Scales -- The Thermophilic Cyanobacteria of the Zerka Ma'in Thermal Springs in Jordan -- Iron-Tolerant Cyanobacteria -- Extreme Acidophiles -- Eukaryotic Community Structure from Río Tinto (SW, Spain), a Highly Acidic River -- Species Composition of Cyanidiales Assemblages in Pisciarelli (Campi Flegrei, Italy) and Description of Galdieria Phlegrea SP. NOV -- A Genomics Approach to Understanding the Biology of Thermo-Acidophilic Red Algae -- Enigmatic Archaeal and Eukaryotic Life at Hydrothermal Vents and in Marine Subsurface Sediments -- Phototrophs Under Water Stress: Dry and Hypersaline Environments -- North American Desert Microbiotic Soil Crust Communities -- Chroococcidiopsis from Desert to Mars -- Chlorophyta on Land -- Aeroterrestrial Algae Growing on Man-Made Surfaces -- The Systematics of Subaerial Algae -- Diversity, Distribution and Ecology of Green Algae and Cyanobacteria in Urban Habitats -- Diversity of Organic Osmotic Compounds and Osmotic Adaptation in Cyanobacteria and Algae -- Adaptation of Algae to Changing Environments -- Cyanobacteria -- Life in a Hypervariable Environment -- Other Microorganisms and Extreme Habitats -- The Fate of Biological Materials in Acidic Environments of the Río Tinto, Southwestern Spain -- Deep-Sea Microbial Eukaryotes in Anoxic, Microoxic, and Sulfidic Environments -- Fungal Associations at the Cold Edge of Life -- The Early Earth's Record of Supposed Extremophilic Bacteria and Cyanobacteria, at 3.8 to 2.5 GA -- Outlook-Summary -- Algae and Cyanobacteria Under Environmental Extremes.