Really weird looking hitchiker
 

I have had some live rock in my tank since the begining of January and it has been cycling without a light until the last couple of weeks. Today when looking at my tank I noticed this large white thing move in my peripheral vision from the surface of the rock back in. I looked in the hole it went into and could not find anything. So..... I thought it might be a worm and started looking at all kinds of worms common to the hobby and since I didn't get a great glimpse of it I came up empty. Then after the lights had been off for a bit I went and turned the lights on and this thing was sticking out of the rock that had a white head about a centimeter across with what looked like two antenna (that were independantly moving over the rock) and the body that was going into the rock was brownish. As soon as I turned the light it quickly went back into the rock.

What is this thing?! I have heard of snails without shells but are they this big and do they quickly move in and out of rock? Could it be a worm?

I will try and get a pic but I do not have a great camera and this thing is really skittish.

Palmer

Hmmmm...now you've made me curious, did you get a pic of it yet?

could be some kind of mantis shrimp.try some krill in front of the hole dont use your bare hand use a rod or something.if it attacks its a predator and you may want to remove it

Haven't been able to get a picture of it yet because it is so reclusive but I am going to try tonight and I am even considering setting up a video camera on a tripod to see if I can record it when I am not there.

I realized after reading what I wrote that it will be hard to suggest what this is without a picture. I dont think it is a mantis because I got a good look at it last night and it doesn't look like a mantis at all. I don't have any experience with sea slugs/snails and nudibranches but my best guess is it is one of these by the appearance. Although because I have no experience with them I do not know how common it is for them to burrow in LR. Another coincidence is I have a Diatom explosion that just happened because it is a new tank and I recently put my lighting in. Perhaps it is coming out of the rock to sample the diatoms....?

Palmer

Likely a Polyclad Flatworm, they are predatory and snack on snails and clams......:sad:

Geez... hopefully not, since I haven't seen the whole thing come out of the rock yet I can't confirm. I looked at Ronald Shimek's inverts book and he say's polyclad's are hard to keep alive in the aquarium so will likely perish? I have digitate hydroids on the same rock so if I find out it is a polyclad worm I may just get rid of the rock. I was planning on waiting out the hydroids because I read they do not last forever and usually cannot live in an established tank for long.

Palmer

Well it isn't as shy as it was I got about 14 minutes of footage on my camera. I uploaded it at the link below. I put about 6 minutes up and the closest and best footage starts at about 2.5 minutes. Since seeing it out of the rock it isn't as long as I thought it would be. It's less than an inch long with two big antenna's and it is feeding on something on the rock with a mouth between the antenna. Still seems like some kind of snail without a shell to me but I am interested in what more knowledgable folks think!

Palmer

http://www.youtube.com/watch?v=vMn-y39-tao

Stomatella varia - beneficial hitchiker. 99% positive. :)

+1, 100% positive (I'll add 1% :) )

+1 positive it a Stomatella, see the hole on the back of the snail towards the rear.

Bill