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The small and colorful boxer crab, Lybia tesselata, grasps a pair of tiny sea anemones in its claws which it then uses for both defense, and to collect food.

Porcelain crabs. The porcelain crabs (Neopetrolisthes), so-named for their smooth, colorful shells, are sometimes called "half-crabs," for they are structurally similar to prawns and lobsters. They are commensals on the giant anemones where, protected from predators, they strain plankton from the water with mouthparts that have been modified for filter-feeding.

Echinoderms

Everyone is familiar with the common starfish or sea star. But starfishes are only one of five groups that together form the Echinodermata, "hedgehog-skinned" animals. The others are the sea urchins, the brittle stars, the feather stars and the sea cucumbers. Most echinoderms have a skeleton of spiny plates— most developed in the sea urchins, and least developed in the sea cucumbers—and five-sided symmetry.

Starfish. The five-sided symmetry of the echinoderms is clearly displayed in the starfishes. Most Indonesian species have five arms, although some individuals may have one arm more or less. The common cobalt-blue starfish Linckia laevigata is particularly variable in this regard. Some of the larger starfishes may have a great number of arms.