The octopus has highly developed eyes and a very sophisticated nervous system. It is thus considered "intelligent," and people find it hard to believe that it is a mollusc. The white color of this specimen suggests exhaustion, and perhaps the photographer was a bit overzealous in getting this shot.

      Trochus. Top shells (Trochus spp.) are relatively large (6-8 cm.), and conical. Before the advent of plastics they were widely collected for the manufacture of buttons. Removing the grubby outer layer of shell reveals the lustrous nacre, or mother-of-pearl beneath. Until the invention of Bakelite, and the many plastics that followed, shell nacre for buttons was an important business in Indonesia. Today they are still collected, most to be used in souvenirs and to supply the small market for "real" buttons.

      Clams and Oysters

      The bivalves include such familiar forms as clams, oysters, mussels and scallops. All have two articulated shell halves that can be closed with a large muscle. It is this muscle that makes bivalves so prized as seafood. With a very few exceptions, bivalves cannot move, like gastropods, and thus most have adapted to filter-feeding. They draw water in through one tube or "siphon" and pass it out through another. This stream of water passes through the animal's gills, which serve the dual purpose of respiration and filtering out food particles.

      All bivalves must hold their shell halves at least slightly ajar to maintain water circulation through their bodies. But when danger threatens they are clamped shut. Some Indonesian bivalves gain further protection by boring into corals and reef rock, so that predators cannot reach them. The boring is achieved by a combination of chemical action and rasping with the two shell haves. Eventually, reef bivalves become so encrusted with sponges, coralline algae, bryozoans and cnidarians that they are barely visible.

      Giant clams. The giant reef clams, Tridacna spp., have a different means of feeding. Like reef-building corals, Tridacna clams harbor zooxanthellae in their fleshy mantles, and can thus "manufacture" most—or perhaps all—of their own food. Like corals, they require lots of light, and tend to be found in the shallows. They grow with the hinge of their shells down, and their rippled gape facing the sun.

      There are seven species of Tridacna, of which the giant clam, T. gigas, is the most dramatic. These animals can reach a meter and a half in diameter. An animal that big could be a century old. Although smaller than T gigas, T squamosa has a beautiful ruffled shell. The fleshy mantles of Tridacna clams are beautiful, varying in color from brown to yellow to green to blue, with contrasting spots or mottling.

      Tridacna clams are a great delicacy in Asia, particularly in Taiwan, and their shells are made into terrazzo in factories in Surabaya. Over-harvesting has greatly reduced their numbers throughout Indonesia. Shallow reefs in Eastern Indonesia that used to support literally fields of giant clams have been stripped in just the past few years. There is fear that the population in many areas is no longer at a self-sustaining level.

      Recently, however, researchers at the Micronesian Mariculture Demonstration Center in Palau, headed by Gerald Heslinga, have discovered a method of "farming" giant clams by inoculating the veliger larvae with zooxanthellae. Once the symbiotic algae is in place, the clams need only a good supply of sea-water and plenty of light to thrive. The farming operation requires little room, and the clams reach 10 centimeters across in just two years. Because of the commercial potential for these clams, a number of pilot farms have recently been established in the Pacific region.