The pteropod Clio pyramidata, a common planktonic mollusk (pteropods) with a shell made out of aragonite, a metastable form of calcium carbonate. [Photo: R. W. Gilmer and G. R. Harbison]. This photo appeared on the cover of Science magazine, accompanying the article by Feely et al. (Science 305, 362—366, 16 July 2004)

Clio pyramidata pulling in its food web at night in the Sargasso Sea. [Photo: R. W. Gilmer and G. R. Harbison]