Help me identify this black sponge thing?

[Nickjwes]

I've had this in my tank for a while but not sure what it is, thought it may be a type of sponge and I realized another rock that has Zoanthids on it has a tiny one that looks identical- help me identify it? Also I don't believe it is harmful to my reef but would like to be sure:

Also they both have two openings (and kinda resemble a barnacle) but their outside is spongy like and they open and close their openings. The one originated on a piece of rock that had mushrooms on it and it stuck on a the rock like an anemone would be but it has yet to move besides opening and closing (seems to fill and expand or contract). Thanks in advance.

 

[Nickjwes]

Possibly some type of sea squirt/tunicate?

 

[bashment]

i had something similar to this on the side of my favia. interested in knowing also what it is

 

[cloak]

Possibly some type of sea squirt/tunicate?

+1

http://www.saltcorner.com/AquariumLibrary/browsesectiongroups.php?SectionID=36

 

[Nickjwes]

Thanks for the link! I have yet to find one that looks like a definite match, but I presume it's a solitary-living tunica based on its solitary status.

The closest match I could find seems to be Ascidia sp. 3:
http://www.saltcorner.com/AquariumLibrary/browsegroupspecies.php?GroupID=225


Here's another pic of the same one covered in some algae the lettuce nudi is feasting on:

And here is one of the little one I noticed recently:

Anyone who has a further idea of specific species I would love to know.

As far as I can tell it's not harmful and I assume as a filter feeder it will just a help with biological filtration.

Not sure if it helps determine the region it came from, but it came on a rock piece that had a hairy green mushroom on it (the real reason I bought it) and maybe another mushroom or so.