It's about 3". Kinda round. These things don't have arms that protrude like normal star fish. I found it in the bucket of rock I got from Living Sea when he was closing. This thing survived quite a trip. I put 140 lbs of rock in buckets,dry,in the back of my pick up, raining, about 50 degrees all the way from Living sea to Weare, uncovered, with a pit stop at AquaAddicts. Then I left the buckets outside for a couple hours. Brought them in. Mixed up some saltwater real quick and threw everything into that rubbermaid with a powerhead and heater, covered it and left it alone until today I decided to look at it. I was picking through the rock when I found a SQUISHY rock....