I had one for quite awhile, until I passed it along to my roommate. The Petsmart "marble" shrimp is indeed a wood shrimp. They can change color somewhat to blend in, and they spend most of their time on a rock or plant with water flowing near it. Still neat, even if they don't move much. $12 worth of neat? I don't know. My roommates old one was found on the floor, and at one point I found mine in my HOB filter.