These are the simplest worms and probably the first to develop bilateral symmetry. They have 3 basic tissue layers. Cnidarians have only 2 layers and sponges have no layers at all, only specialized cells. Flatworms breathe through the body surface and the mouth functions also as the anus. Their only sensory organs are tiny eyespots on short tentacles. Marine flatworms are often brightly colored and move forward by the beating of cilia in a slime print secreted by the worms' underside. They are hermaphroditic.

Divided Flatworm
(Pseudoceros dimidiatus)

This is a conspicuous diurnal black, yellow and orange flatworm that is surely distasteful. It has a double yellow line down the center of its dorsal side.

Fuchsia Flatworm
(Pseudoceros ferrugineus)

This is surely one of the most colorful animals on the reef. It is brilliant fuchsia, trimmed with scarlet and gold, and dorsally speckled with white spots. Its bright color serves as a warning that it is distasteful or toxic.

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