Wow - I am so thrilled that so many of you already hopped on here to try and help - and so FAST, too! What a great forum!
Honestly I couldn't tell you what it feels like (yet). I've only had the tank and rock for about 3 weeks and didn't notice it at all for most of that time. Then the other day I reached in to just "rearrange the rock a little bit" and, well, you know how THAT goes. Before I knew it I was rearranging ALL the rock and starting the aquascape from scratch. When the cloud cleared and I was staring in the tank that night with magnifying glass and flashlight I noticed this thing - hadn't ever seen it before, probably because it was up against the rear wall of the tank. Now it's STILL not real easy to see or get to but I will reach down and touch it next time I'm putzing around in there. I don't know if this is good news or bad news but I just discovered what I think is another one at the other end of the rock. The yellow tip isn't as pronounced, not as yellow and not as protruded, but it looks like it's trying to grow one.
Thanks for responding so quickly - I'll try to get better pix somehow.
Sue