An estimated 71% of planet Earth is ocean, home to more than 230,000 species of fauna and flora. This photo gallery includes impressive pics of over 75 marine invertebrates, including cephalopods, crustaceans, mollusks, echinoderms, and more cool animals. Octopuses, crabs, jellyfish, and starfish may be the main attractions at public aquariums, but there is much, much more to the deep blue sea. For example, there are more than 3,000 unique species of nudibranch (NOO-dee-brank) sea slugs, many in impossibly bright colors that warn predators that they are poisonous. On the other end of the spectrum, the predatory flamboyant cuttlefish and peacock mantis shrimp boast bold colors to distract prey while they use unique tactics to stun and kill them. It's all very ghastly. Enjoy these fascinating photos of sea creatures you never knew existed, and never forget that the ocean is a dangerous place!