Center: Cyclotella cryptica (view from the girdle band) from the Sammlung für Algenkulturen at Göttingen, Germany (SAG, strain 1070-1). Micrograph by Renate Kort, Geomicrobiology, ICBM, Carl von Ossietzky University Oldenburg, Germany. Interference contrast. See article by Janssen et al. this issue pp 27–33. (Magnification, ca. 5,000×; cells 5-10 µm)

Upper left: Transmission electron micrograph of bacteriophage Ø29. Negative staining with uranyl acetate. From Margarita Salas, Center for Molecular Biology "Severo Ochoa", CSIC-UAM, Madrid, Spain. (Magnification, ca. 200,000×)

Upper right: Scanning electron micrograph of square haloarchaea observed in Santa Pola, Alicante, Spain, solar salterns. Micrograph by Silvia González-Acinas and Josefa Antón, University Miguel Hernández, Alicante, Spain. (Magnification, ca. 25,000×)

Lower left: Transmission electron micrograph of Ostreococcus tauri in division. This protist, the smallest known free eukaryotic cell, was identified by C. Courties and M.-J. Chrétiennot-Dinet in Thau Lagoon, France, in 1995. Micrograph by the same authors, from Arago Laboratory, CNRS, Banyuls-sur-Mer, France. Diameter of the dividing cell 1.2 µm (Magnification, ca. 70,000×)

Lower right: Micrograph of several Dematiaceus fungi hyphae from Rio Tinto, Spain. They are acidophilic and resistant to several heavy metals. Micrograph by Ricardo Amils and Anabel López-Archilla, Autonomous University of Madrid, Spain. (Magnification, ca. 400×)