MARINE BIOLOGY : *INVISIBILITY CLOAKS*

THE OCEAN is dark and full of terrors, and the black dragonfish is the darkest of them all. Its surface, new measurements reveal, is as black as the blackest material known - the result of an abyssal arms race.

''The trick to being really dark is to control the scattering of light,'' says Sonke Johnsen of Duke University, in North Carolina, who studies the dragonfish. ''You have to let light into a material and let it bounce around a lot.''

Black velvet, for instance, appears darker than other fabrics because photons [the particles of light]  skip between its fine hairs and do not escape.

Similarly, Vantablack, the least reflective artificial material, traps photons in a forest of carbon nanotubes standing on their ends. It absorbs 99.965% of visible light. Objects coated in it seem to disappear, leaving behind an inky silhouette.

Karen Osborn of the Simthsonian National Museum of Natural History, in Washington, D.C, noticed a similar effect when she tried to photograph a deep-sea fish, many of which are coated in a fragile black film that has to be removed before a picture can be taken

Under a scanning electron microscope, she discovered that this film is made of millions of  microscopic melanin granules shaped like the drug capsules, capped by a thin gelatinous layer.

The absorbing effect of the film is so great that instruments caliberated in the usual way cannot detect any light from the fish at all. Dr. Osborn's attempts to measure the light inside an empty pitchblack room yielded the same result.

Eventually, she and her colleagues worked out that the dragonfish reflects just one in every 2,000  photons incident upon it - an absorption of  99.95 %. Similar measurements hold true for a whole range of  fishes brought up from the abyss.

The Honor and Serving of the  latest Operational Research on Marine Biology continues. The World Students Society thanks The Economist.