Help ID my crab, sorry no pictures

I definitely didn't put him in, he is large enough to drag around a huge turbo snail shell with ease. He he has a light green body, long yellow antennae, the two feelers between the eyes are neon blue, large round pitchers, and purple tips on the legs. If I had to guess he would be larger than a quarter out of the shell.
 
generally crabs with sharp tipped pincers are predatory and not good for reefs, but without pictures it would be difficult to say for sure what it is. For instance, porcelain crabs have sharp tipped claws but are not predatory, rather filter feeders. As I said, we would really need to see a pic to give a more more solid ID.
 
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