Slug right?

[FreakinReefin]

Slug and something....

I am pretty sure this is a nudibranch of some sort, however my bigger question is if it is bad or good. This is a macro shot and the slug was maybe 1-1.5mm in length. I have found several of these in my refugium/frag tank and I am worried they may cause some damage...help!

 

[FreakinReefin]

Also this one...

I think this might be a sponge of some sort...but I have these growing all over my refugium and I am not sure if they are sort of egg sack for some lethal invasion squadron just waiting to kill everything. Okay, a bit dramatic, but you get my point.

 

[ashton]

I think this might be a sponge of some sort...but I have these growing all over my refugium and I am not sure if they are sort of egg sack for some lethal invasion squadron just waiting to kill everything. Okay, a bit dramatic, but you get my point.

The 2nd pic looks like a Pineapple sponge. I would get them growing in low light areas of my tank.

 

[returnofsid]

Second pic is a pineapple sponge. Completely harmless.

First picture is a nudibranch or slug, which most of are harmful...however, it looks an awful lot like a berghia nudibranch, which will only eat aiptasia and will starve and die without it. They're a light gray/brown color when well fed, but as they start to starve, they lighten up in color, eventually turning almost pure white before dying.