Not sure what it is, but thought I should mention in case you don't know yet, but zoanthids contain a potent neurotoxin and to *some* folks, it can be a serious issue. Google "palytoxin zoanthids" and you find a bunch of articles.
While I've gotten a little more laid back with my use of gloves in my tank, whenever I handle zoanthids, latex gloves are a mandatory thing for me. Just figured I should mentioned that in case you didn't know it.
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