I have something similar, when I asked around I was told it’s a stomatella and everyone had nothing but good things to say about them. Apparently there really good CUC and can not be purchased. Only way to get them is by hitch hiking
When my one n only hitchhiked it’s shell was the size of a pinky nail now, it’s about the size of a thumbnail. It’s grown a lot and just grazes non-stop.