Flatworms are some of the most colorful marine creatures. Their spectacular colors and patterns can be eye popping. Scuba divers and tide-poolers love to take pictures of them for good reason; they are dazzling.
These ferocious predators are found in all habitats, feeding on tunicates, small crustaceans, worms, and molluscs. Some species have coloration that mimics other animals or acts like camouflage. But most are very colorful and easy to see. This is an example of warning coloration (called aposematism), advertising that the flatworms are poisonous to eat. Some species contain tetrodotoxin: the same poison found in a number of other poisonous creatures, including puffer fish, some species of frogs and the blue-ringed octopus.