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The thorny oyster ("Spondylus sp.) is often so encrusted with sponges, algae, tunicates and other organisms that only when it is agape with its bright mantle showing (as here) can it be seen. Halmahera, Maluku.

Oysters. A number of oysters can be found on the reef, in many cases so well camouflaged with encrusting growths that they are at first invisible. The cock's comb oyster (Lopha cristagalli) has a distinctive sharp, zig-zag opening, and is often covered by encrusting sponges.

The colorful mantle of the thorny oyster (Spondylus spp.) stands out, although its rough shell is usually overgrown with algae, sponges, and small cnidarians.

In many parts of Indonesia, Japanese operators seed pearl oysters (Pinctata) and hang them in the shallows to grow pearls. The oysters are purchased from local collecters, and the "seed" comes from a freshwater mussel found in the Mississippi basin. Security on these "farms" is high, and divers are unwelcome.

Cephalopods

These animals, despite their close relationship to the snails and clams, are active, "intelligent" predators with highly developed eyes and sophisticated behaviors. The octopus has eight suckered arms, while squid and cuttlefish have an additional two grasping tentacles. Both octopi and squids have a hard, chitinous beak. The nautilus—of which only one genus is extant— differs markedly from the other cephalopods. It has 90 arms, without suckers, and a well-developed shell. Unlike other cephalopods, the nautilus has very primitive eyes, lacking a lens and open to the water.