HUGE flat slug

[SurfTrack]

Ew what is this huge flat slug thing? I saw it last night, I shone the light on it and it seemed to irritate.

It’s maybe 4 inches long.

 

[Timfish]

Flatworm. Pretty cool. They are rare but some can cause problems. If you haven't added anything in months and haven't had any problems with anything I'd leave it myself.

 

[Naso180!]

I had one looks exactly like that in a 75g about 10yrs ago. Pretty cool. Showed up in the dark, seemingly from no where. Saw it maybe 10 days in a row. Then just disappeared as quickly as it appeared. Never saw it bother any coral or do anything other than speed up to hide in full light.

 

[Soren]

Probably a polyclad flatworm, to be more specific.