This isn't the first time I have seen this but I got some pictures this time. Basically the high grade CRS was dragging the Planaria around the sponge and then the lower grade came along and they both started pulling on it and then the highgrade grabbed it back for himself. I looked and from everything I could tell the shrimp was grabbing the Planaria and not the other way around, the planaria appeared to try to get away a few times also.