For those that keep Acropora sp, they've heard of Acropora Eating Flatworms (AEFW) - Amakusaplana acroporae. The best way to identify if your coral has these it to place the coral in a white container with tank water and a few drops of Lugol's Solution. Wait a minute, then use a turkey baster to blast the coral. If you see small oval flat disks flying off the coral, it is infested with AEFW. These are a real threat, and will consume all Acropora sp. in the tank. The above picture points out just how small they are, and that doesn't even include the eggs! Please refer to this page for more information, as this continues to be the biggest threat SPS-keepers fear. NOT reef-safe!
AEFW officially gets its scientific name (April 2011): http://www.reefaddicts.com...flatworm-has-a-name-Amakusaplana-acroporae