What kind of flatworm?

[Meloco14]

Last night I noticed two little white flatworms. They were on the glass, and seemed to be grazing algae. They were milky white, about a cm long and 1/8" wide, and had V shaped tails. No apparent eyes. No markings of any kind, just white, and they moved pretty quickly, faster than a normal snail. Are these bad? Or just algae grazers? TIA

 

[Anonymous]

We realy need a picture, but it does sound like one of a couple species of white Acoel Flatworms.
How long has your tank been set up and how is your sandbed population ?
One of these species preys on copepods and excess food items.

http://www.rshimek.com/odd_critters.htm#Flatworms

Regards,
David Mohr

 

[Meloco14]

thanks for the link. I'm almost positive they are the ones in the bottom right picture in the original group of 5 pictures on that site. The text doesn't mention much about them axcept this, "The lower right image is a composite of three photos of a small white flatworm, which eats some of the brown flatworms found in many reef tanks. It may also eat the red planarian, but this is uncertain, and experiments are being done to confirm this." So from this it seems that this guy is fairly harmless, maybe even beneficial by eating other flatworms. I will try to get a picture if I can. BTW, the tank was just recently set up, the live rock is all new, about 3 weeks post cycle, but the few corals, fish, inverts, and all the sand is from an established tank i've had running for a year. I think the probably came in on the new LR, as I've never seen them in the old tank. Thanks for the help