The Indo-Pacific acanthopterygian fish family Pegasidae (order Gasterosteiformes) is reviewed and found to contain 5 species in 2 genera, Eurypegasus Bleeker and Pegasus Linnaeus. Eurypegasus contains 2 species: E. draconis (Linnaeus), ranging throughout the Indo-Pacific Ocean from the Natal coast of South Africa and the Red Sea to Tahiti and the Marquesas Islands; and E. papilio (Gilbert), restricted to the Hawaiian Islands. Pegasus contains 3 species: P. laternarius Cuvier, known from Sri Lanka and Indonesia to southern Japan; P. volitans Linnaeus, from South Africa and the Persian Gulf to Japan, the Philippines, and Australia; and P. lancifer Kaup, restricted to temperate Australia and Tasmania. Although, E. papilio has been collected in bottom trawls fished as deep as 152 m, pegasids commonly occupy relatively shallow, coastal waters, where their horny depressed bodies, subterminal mouths, coloration, and large, horizontal pectoral fins make them well adapted to a benthic lifestyle. Larval and juvenile pegasids (up to 30 mm) occur planktonically throughout the geographical range of the adults.
A key to pegasid taxa is provided. Annotated synonymies, including references to all pertinent pre-Linnaean literature, are given for each species, followed by a diagnosis, description, and comments on individual and geographic variation, ontogenetic change, nomenclature, and geographic distribution. All taxa are illustrated and their geographic distributions are plotted on charts.