Transparent Animals; February 2000; Scientific American Magazine; by Johnsen; 10 Page(s)

Flamelike, iridescent colors appeared on a hydromedusa of the genus Arctapodema (large image at left) when the light from the photographer's strobe shone on fine muscle striations on the animal's body. The transparent snail Pterosoma (lower left corner) has an elongated retina that takes in images line by line, like a television camera.The photograph next to it shows a creature so recently discovered that it has not yet been named. It is a comb jelly, of the phylum Ctenophora, which paddles through the water by moving the comb plates along the edges of its body. The amphipod below, known as Cystosoma, resembles a five-centimeter-long crystalline roach. Its exterior shell encloses mostly water, as well as a tiny, needlelike vertical gut that is not visible in this image. This transparent octopus, Vitreledonella richardi (right), is also rarely captured and little known.

Some transparent animals use their invisibility for more than passive camouflage. Siphonophores are peculiar relatives of jellyfish-half-individual, half-colony. The best-known example is the Portuguese man-of-war. Most are transparent, but some have colorful stinging organs that mimic the appearance of baby fish, small shrimp and other alluring prey. Animals pursue these organs, unaware of the much larger transparent animal they are attached to, and are quickly killed. Above, a creature of the taxonomic group prayid is shown in a compressed state, only about 10 or 12 centimeters long. The light-colored objects inside it are stinging cells. In hunting mode the animal transforms itself, stretching out to a meter in length, with the stinging cells dangling, netlike, off buoyant organs. Another siphonophore, Forskalea (right), is a close relative of the Portuguese man-of-war; it hunts in much the same way as the prayid does.