Looks like flat worm??

Can anyone please id this, i think it's a flat worm just by looking but can anyone tell me what type and is it bad, it's about 5-7inches long w/o stretching, found it under a rock when doing a tank cleaning/water change.

 

i dont know what it is, but nasty!!! im gonna have nightmares now, thanks for that......

 

That there is a HUGE bristleworm. I would remove it and put it in the refugium if you have one.

 

wow, thats a monster bristleworm.

 

thats a baby bristleworm, they can get much bigger. good thing your wearing gloves.on the site the first two critters are flatworms
Pests Invading the Reef Aquarium Hobby: Part 2 - Flatworms, Snails & Limpets

 

baby? yeesh....

I don't want to meet it's mom..

 

some get to 18"
Polychaete Annelid Identification, or “You Can Always Tell A Bristle Worm… by Ronald L. Shimek, Ph.D. - Reefkeeping.com

 

This worm is on my 72bf that is at my ex gf's house, she doesn't have a refugium but i'm inprocess of finally getting to using the large part in my sump as a refugium, so should i just throw it in there or just leave it in her tank and just watch to see if it does any harm, also while we are talking refugium what's the best route a 2-3 in sand bed with what in it???

 

I wouldn't leave it in the main tank. They can get a bit aggressive when they get that large. As for what to put in a refugium, I use a 4" sandbed and a variety of calupra.

 

Until I saw the bristles - that 1st pic made me think of a leach! yek...