Xenia in trouble?

[Cyclura]

My pulsating xenia has developed some brownish/blackish spots on the undersides of the some of it's polyps. I guess you could call them the "flower petals" but anyways, the xenia is open and pulsating like mad and seems extremely healthy. Yes i know it would be better to have a picture but my camera just wont capture it. Maybe im being a little too observative? any ideas as to what this is?

[fat walrus]

Keep an eye out for nudibranchs.

[Cyclura]

Now that you mention it...i have always noticed the odd "slug-like" critter here and there in my tank but lately i havent seen any at all (within the last few weeks). Could these be nudibranchs and is that whats causing my xenia to do that it's doing? and if so...how to i get rid of them?

or could it be the "peppermint shrimp" that i have munching on my xenia? It turns out i was tricked..again and the store sold me a camel shrimp and not a peppermint. I hear that they will eat corals...but there arent any huge abrasions or anything, just a few black spots...kinda like there would be if the "petals" got burned and are charred a bit.

[CarmieJo]

Every once in a while my xenia encroaches upon my BTA's space and gets stung. The "petals" get black and shrivel up but seem to recover in a few days.

[fat walrus]

Get rid of the camel shrimp. Keep your eyes out for that slug-like thing that you saw, many predatory nudibranchs tend to look like their prey.

[Cyclura]

how do i get rid of them if they come back? could it possibly be aiptasia stings?