Maybe a nudibranch?

James Fox · Jun 26, 2018

I got my live rock from Tampa Bay Saltwater, so it's just packed with hitchhikers, which I kinda like. Had a few aptasia, but then also lots of starfish, crabs, sponges, corals and other cool things - including lots of things that are bioluminescent at night like fireflies, but I can't figure out what they are.
Anyway, I am about 3 weeks in and just saw this fellow on the glass briefly. Should I remove him if I see him again? Maybe 1.5cm long.

Crabs McJones · Jun 26, 2018

Definitely a nudibranch. Not sure the exact type. @KJ may know

corey01 · Jun 26, 2018

definitely a nudi. quick and dirty way to check if he is dangerous is turn your actinic bulbs on when he is out, if he fluoresces its due to the zooxanthelle he is likely eating from your coral.
very likely the color he shines if he does will match up to the color of what coral he is eating/ if he is eating it at all.
if not chances are he eats something like sponges or a multitude of other possibilities. I have never heard of them being dangerous to fish.
I have had some very cool ones in the past. my favorite was a charcoal black nudi that ate black sponge growing in a crevice in my rock.

Crabs McJones · Jun 26, 2018

corey01 said:
definitely a nudi. quick and dirty way to check if he is dangerous is turn your actinic bulbs on when he is out, if he fluoresces its due to the zooxanthelle he is likely eating from your coral.
very likely the color he shines if he does will match up to the color of what coral he is eating/ if he is eating it at all.
if not chances are he eats something like sponges or a multitude of other possibilities. I have never heard of them being dangerous to fish.
I have had some very cool ones in the past. my favorite was a charcoal black nudi that ate black sponge growing in a crevice in my rock.

Good tip! I never knew that