WHAT ARE FLATWORMS?

Small reddish-rust colored creatures that may already be in your tank.  Can can alsome come in as hitchhikers when you buy a new coral or fish. They can be seen on the glass or acrylic, on the substrate, or on live rock. They have extremely thin bodies, thus the name flatworm. They appear almost two-dimensional, barely a flap of skin. They can move through the tank, elongating the front part of their body like a sail filling with wind, latch on to the nearby surface and pull the rest of it's body forward.

They feed on small foods like rotifers, phytoplankton and such, and will grow out of control unchecked. Creating a mat with their bodies, they can smother corals or parts of the substrate. If they get to the point of overpopulating the tank, there is the possibility that they may die suddenly all at once, and the toxin they release at death can cause further deaths and even wipe out a tank entirely. Some predators exist, but results vary. Six Line Wrasses, Leopard Wrasses, Target Mandarins and even Blue Damsels reportedly eat these flatworms, as does one Nudibranch (Chelidonura varians), but there is an easier way to get rid of them.

Flatworms covering a rock