If touched by humans, sponges have been known to cause skin irritations. B. Marine Worms Flatworms are one of the littlest known inhabitants of tropical marine S.E.A. reefs. They come in many exotic colors and forms. Octopods and squid move by jet propulsion. This group contains about 35,000 species, many of which are fished for commercially.
Oysters are mollusks that produce pearls, which are, of course, very valuable.
This silt 'chokes' the reefs and eventually kills them. The reefs of S.E.A. are some of the largest reefs in the world and special attention must be taken to preserve these ecosystems. Many fishermen use dynamite and cyanide, the latter being a very toxic poison to collect fish for aquariums. When they inject cyanide into the reef, it anesthetizes and puts the fish to sleep for easy collection. A fisherman will then break apart the reef to get at creatures that hide in the crevices of the reef.