National Geographic : 1957 Jan
On Australia's Coral Ramparts more in length and hundreds of pounds in weight; such giants are not found in the Barrier's southern waters. Clams of the genus Tridacna seen on the Heron reef range up to the size of an American football and are so abundant that if one were to count all he saw during the course of an hour's fossicking, the figure might run into hundreds. Clams Blaze in Brilliant Hues But what the tridacnids here lacked in size, they made up for in color. With "mouth" and mantle facing upwards and with the hinge and base of jagged valves half or wholly em bedded in the coral, each clam sits on the reef in a fixed position. At low tide many protrude above water, their valves shut and all their tissues with drawn into the locked interior. Thus closed they display no color whatever. But when observed through several inches of the reef's window-clear water, valves gap ing and mantle tissues exposed, they are one of nature's loveliest sights and a dye mixer's dream. No two are the same. The mantle of one will be electric blue, another just as intensely green, or yellow, mauve, or orange, with these colors in infinite combination, and mottled, striped, and speckled in every con ceivable design (page 15). Although clams have no eyes like those of the vertebrates, they do have light-sensitive organs that can detect the moving shadow of Page 12 - Stonefish's Arsenal of Terror: Loathsome Face and Lethal Sting Amid the delicate loveliness of the reef lurk sev eral of the world's most fearsome hazards. As venom ous as a cobra is the stonefish (page 16). Rarely does the visitor see a stonefish, for it lies motionless in the sand, a perfect counterpart of a piece of weathered coral. If prodded, it moves slug gishly. But should an unwary wader step on the fish, thirteen needle-sharp spines bristle erect to inject virulent poison. The victim suffers immediate and unspeakable agony; he may become demented from pain. Death can easily follow. Warty skin, which sheaths the bluish spines even when erect, has been pushed back in this view. The eyes, hard to spot among the many folds and excres cences, are dark dots beneath the pearl-like knobs (magnified 2/2 times). -The author saw two stonefish during five months on the reef; other scientists on longer stays have never spotted one. Dr. Zahl displays one of his finds still alive. Mounted, it now glowers from a shelf in his New York home. © National Geographic Society a man. As we made our way across the reef we frequently heard the sound of alarmed clams snapping shut, their action so rapid that water from their siphons often shot several feet into the air. If we stood very still for a few seconds after such a demonstration, we were rewarded by seeing the clam slowly opening again, its gorgeous mantle creeping out over the toothed edges of the valves. Adding to the scene set by the brilliant clam mantles were colors of a different order-those of the coral, perhaps more subdued but cover ing as wide a range as the flowers and vege tables in a spring garden. There are numerous species of reef-building coral, and each one may assume a variety of hues and forms-from a forest of bristling staghorns acres in extent to a bed of sprout ing asparagus.