I have no experience whatsoever with crabs, but from running a quick search, red clawed sounds like it's the most likely, based on similarity in name, red claws in the pictures and "one of the most popular crustaceans". Fiddler crabs are what seem to be the most popular but the picture you've posted doesn't seem to look like anything that came from a search.
My concern is that nothing came up with that genus-species name. Not sure if you found it too, but a couple of PDF documents come up in a google search and I quickly skimmed through one that said Parathelphusidae is a family that is very little known about, however it is from Sri Lanka which runs true to the info given. But I checked the wikipedia page and there was no Enthropus identified
Red boxer crab definitely doesn't sound right either. Red box"ing" crab shows results for a saltwater crab - more commonly known as strawberry crab - and looks nothing like your picture. Is the store this photo was taken in usually reputable? I'd probably ask for more information from them about it.
Also from searching it appears that there are very few fully aquatic crabs, and they're a rarity. Seeing as these guys look really cheap from the photo it makes me think they're not rare. You'd be needing some dry land for them. Giving them some "shoreline" is obviously the best way, but I did find this which looks like it could work? I'm unsure about oxygen needs though.
http://m.instructables.com/id/Under-water-Dry-zone-for-fiddler-crabs
Again I have no experience other than my past 20 mins of reading, if someone comes along who knows what they're talking about has advice by all means take theirs. But good luck with it all, I found crabs to be some pretty interesting reading.
Edit: if they're your LFS/LPS could you get a picture of them in the tank to help? Also, more research shows the Perisesarma genus is a possibility, possibly P. samawati or P. guttatum