Center: Lyngbya aestuarii LIEBM., a benthic filamentous cyanobacterium that lives in the intertidal ponds of the shrimp production operation at Ensenada de Aripez, Baja California Sur, Mexico. Trichomes 8–16 µm in diameter, sheath firm, yellowish. Micrograph obtained with a Nikon Labophot phase-contrast microscope with Kodak Gold 100 film by Alejandro López-Cortés The Center for Biological Research of the Northwest (CIBNOR), BSC, Mexico. See article by López-Cortés, A. et al. this issue pp. 227–236. (Magnification, ca. 1170×)

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×)