Examples of common red fluorescent invertebrates on coral reefs. a-d. Stony corals (a. Goniopora, b. Mycedium, c. Fungia, d. Porites). e. Reef scenery, as seen through a Lee Medium Red filter. f. Unidentified alga (white pingpong ball as reflectance reference). g. Calcareous alga Amphiroa. h. Polychaete worm Sabellastarte indica. i. Typical environment of S. indica under reef ledge. Pictures a-d and f-h show object under natural illumination (left) and as seen through a red filter (right). Pictures e and i show fluorescence in the field as seen by a digital camera. Most pictures taken in the field (Dahab, Egypt) under natural illumination between 14 and 17 m depth. Only c was photographed in the laboratory. Other reef invertebrates seen to fluoresce were sponges (e.g. Aaptos, Acanthella, Theonella) and feather stars (e.g. Colobometra, Oligometra).