Please identify

[Jaws]

I was staring at my tank last night in the dark and saw something for the first time. Crawling out of one of the rocks was a long slug-like looking thing that appeared like a pyramid with a plateau for the peak. The part I could see was about 4" long and slowly disappeared into the rock. The design on the plateau looked like a snow pea when you break open the shell. No I was not drunk or under the influence of any kind of narcotic. I can't afford anything like that once i'm finished spending all my money on my tank. I'll take pics if I can find it again. Any ideas?