The orange ones I beleive get about 1foot with a 2-3 inch disk. I would say mine is half grown. I had a micro brittle hitchhiker a few months ago. It only had 3 legs and came on a rock with an anemone I got for the nem. I watched it drop off and go into my rockwork. The other day I saw a bunch of thin little looking banded arms. So I hope I see so.e out of the rocks soon. Check out my build. I posted a big update yesterday.They look pretty cool, how big do they get. The little serpent star in one of my pics was a hitchhiker! I was excited to see him, very small at moment, maybe 3/4” tip to tip.