Common names: Acoel Flatworm, red planaria

Nuisance organisms because they can quickly grow to plague proportions by reproducing asexually. In large populations they can block necessary light from corals. They contain zooxanthellae and will thrive under bright light and are small in size (3-6 mm in length). Dead flatworms emit a toxin that can be deterimental to a system, therefore siphoning is important.

Some methods of control: Heavy skimming, chemicals, strong water flow, manual siphoning, natural predators.