You can't just place it on top of the ric and expect it to eat, although that works sometimes. What I do with mysis is wiggle the shrimp on the tentacles in one particular area of the ricordia. This way you're mimicking the prey wiggling in its tentacles as if it is struggling and then it should start to close up. However, my purple discosomas sp. have pretty much stopped taking mysis. Only my ricordias take mysis.