Is this a sponge?

[Surskit]

I've been looking at quite a few posts on here and I can't tell if this creature that appeared in my tank is a sponge or not. It's a different color than all the other ones I've seen, because it's red with white frills, and it doesn't match the description of location on the common tank hitchhikers thread, being in a fairly low flow, non-shaded area of the tank. Here's a little video I took of it, too, where it can be seen in motion. It's pretty active for how low flow the area of the tank really is.

 

[sixty_reefer]

Most probably a species of nudibranch

 

[Surskit]

Most probably a species of nudibranch

Oh, interesting! I hadn't thought of that. Should I take it out/quarentine it or would it be fine to keep there? At the moment I don't have any coral for it to prey on, as I've been having some real issues with water quality, but I have some fish and inverts.

 

[sixty_reefer]

Oh, interesting! I hadn't thought of that. Should I take it out/quarentine it or would it be fine to keep there? At the moment I don't have any coral for it to prey on, as I've been having some real issues with water quality, but I have some fish and inverts.

Most nudibranch will starve in aquaria, it will be up to you. I had plenty of them in the past as hitchhikers and all end up disappearing

 

[taricha]

I've been looking at quite a few posts on here and I can't tell if this creature that appeared in my tank is a sponge or not.

looks to me like a dead bit of something, or leftover food overgrown by bacteria.