Clam encrusted with Zoanthids

[labernathy]

So, I went to Creation yesterday to purchase my first piece of coral. I wanted to get something low maintenance to get my feet wet with the coral keeping side of the hobby. They had some very pretty pieces labeled as Vietnamese Zoanthids. They were reasonably priced for the size of the pieces compared to what I had seen elsewhere so I decided to get one.

I get home and get it acclimated and placed in the tank. After that, much to my satisfaction it began opening up immediately. So, of course I am sitting here watching it open up and I noticed that a portion moved. Upon closer inspection, it has a small(~1" visible opening) clam! (see picture with the red circle)

My question is, based on the pictures can anyone tell me if they know what type of this clam might be and what I need to do to care for it? I was not at all prepared for caring for this so any information anyone can provide would be greatly appreciated.

Tank information:
26 bowfront and the piece of live rock everything is attached to sits about 6 inches under the water with moderate flow.
Lights are http://www.amazon.com/Current-USA-Marine-Aquarium-36-Inch/dp/B00GFTNG3S/ref=sr_1_2?s=pet-supplies&ie=UTF8&qid=1394832022&sr=1-2&keywords=Current+USA+Orbit+Marine+Aquarium+LED">Amazon.com: Current USA Orbit Marine Aquarium LED Light, 24 to 36-Inch: Pet Supplies@@AMEPARAM@@http://ecx.images-amazon.com/images/I/418hTJlAfbL.@@AMEPARAM@@418hTJlAfbL</a>
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[y-not]

Seeing as how we can not see it, I've no idea.
Sounds like a pretty cool "WIN!!!" to me.

 

[kstyle13]

I bought a large colony of Vietnamese zoanthids that came in today at my lfs. I mean 200 plus polyps. And viola there is a clam on mine as well!!!!! He's about 1.5 inches. Very exciting

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[dawgface]

I don't see a mantle, could be just the shell.

 

[labernathy]

It is possible that it was water movement but i don't believe so because it is very unpredictable in its movement.

 

[sea atlanta]

kstyle13;942474 wrote: I bought a large colony of Vietnamese zoanthids that came in today at my lfs. I mean 200 plus polyps. And viola there is a clam on mine as well!!!!! He's about 1.5 inches. Very exciting

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There are a HUGE number of bivalves that hitchhike in on wild colonies. Typically, only tridacnid clams expose their mantles like we want and typically see.