Cover photograph (Copyright © 2005, American Society for Microbiology. All Rights Reserved.): Scanning electron micrograph of a coccosphere of Emiliania huxleyi, composed of plate-shaped calcium carbonate coccoliths. This photosynthetic marine alga synthesizes these elaborate calcite structures internally and extrudes them onto the cell surface. E. huxleyi is thought to play an important role in the ocean's global carbon cycling today and over the past 200,000 years. Interdisciplinary efforts focusing on understanding the mechanisms with which E. huxleyi controls the design and synthesis of these biomineralized structures may lead novel materials science and biomedical devices. (Photo taken by Jeremy Young; magnification, ×12,000.) (See related article on page 2564.)