Symbiodinium (Brown veins in giant clam)
•A long time ago (Over a billion years) the only life on earth was bacteria that lived in the ocean. Some of these bacteria swallowed others but instead of digesting them they kept them alive and they became a part of them. Some of these fused bacteria (protists) then became plants, animals, amoebas, and planktonic animals known as dinoflagellates.
•These dinoflagellates had two flagella (tails, we have one attached to our sperm) some became armoured with star-like spikes (star sand), others form those reddish/brown slicks that we drive past on the way to the reef and others were swallowed by much larger animals and lived inside them.
•These symbiotic dinoflagellates have been given the genus name Symbiodinium but are commonly known as zooxanthellae and they have been living inside a variety of prehistoric animals for millions of years (surviving the dinosaur extinction and the even more catastrophic Permian extinction) and now they live in the sea anemones, jellyfish, nudibranchs, flatworms, sponges, giant clams and corals of the reef. They are golden brown in colour and there are hundreds of thousands to millions of them in one square cm of skin.