I used to have two crocea. They did well for 5 years until something killed all of my clams last year... One of them would readily attach to any surface under it or push itself off it it wasn't happy. The other one which was slightly larger never attached to anything and never fell either. Here is the underside of the one that never bothered to attach. If yours looks significantly different there might be a problem. The other picture is a little devise I made out of PVC pipe to keep clumsy clams from falling over.
