My poor button polys... help please

[depeche]

Hello, I have had what I think are 'button polys' for well over a year now and they've been fine. To be honest, I'm not possitive that they're 'button polys', but that seems to be the closest thing I can find via pictures on the net. Here are some images that look fairly close to mine:

http://www.exoticfish.com/img.cfm?s=full&id=43225
http://ayreef.tripod.com/pictures/0319/green_button.jpg

Mine have a very deep, cup shaped 'head', and a fairly long 'body' (or tube). They are brown, with a small bit of green in the middle. They close up very quickly if the aquarium is bumped, or if they get some food. And they grow in a colony as in the pictures above.

The problem is this... over the last few months, the tentacles they have around their perimeter have all but disappeared. They now look like little 'nubs' around the perimeter. Sort of like how zoo's have little nubs. Here's an image that looks similar to how mine have changed:

http://photos.thedocwat.com/albums/fish/Button_Polyp.jpg

Note the different in the length of the tentacles in this image and the first images in this post.

Does anyone have any ideas what's going on here? Is this natural? Is it something that happens as a result of changing water chemistry? Could shrimp be eating the tentacles? Or maybe fish?

During the time period in which the tentacles have disappeared, I can't really think of anything changes. No new fish, inverts, corals... nothing. I don't monitor chemistry religiously, so the chemistry might be changing a bit, but I've kept up my normal routine so I'd be surprised if it has changed all that much.

Any help would be greatly appreciated.

Thanks!

 

[thekingfish]

I've heard that they get longer frills with more flow.
How much flow are they getting?

 

[Juanfer]

do you have any peppermint shrimp???
sometimes they eat the tentacles.

 

[ronj]

have you changed the lighting or bought new bulbs???

 

[Ashlar]

I agree with thekingfish. I've seen it in action. I had a colony in the direct flow from a powerhead, that had long tentacles. I split the colony and moved it to a calmer spot, and eventually the tentacles shortened.

 

[depeche]

Well, lighting hasn't really changed (130 watts of power compacts over 30g). The flow *might* have changed a bit. I'll up the flow and give it some time and see what happens. And yes, I do have a peppermint shrimp. Maybe I'll see if I can catch him nibbling on anything at night... but that's sort of like finding a needle in a haystack... can't stay up staring at it all night.

Well thanks you guys, this gives me something to go on!

 

[aquarookie]

Yeah, I agree with "upping" the flow. It might take a while to see change, though... Good luck