To be honest, G. platysoma are not the thoughest stomatopods. I have kept many and rarely to they last more than a year in captivity. I don't know why. I just had one molt about three weeks ago. It looked fine although it did not eat for a couple of weeks - and then died. Given its habitat, I would expect them to be a bit more robust in captivity. On the other hand, I think they are one of the most dramatically colored of all stomatopods. They are also great fun to chase down on a reef flat!
Roy