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No good guess from the photo but the way it is holding its arms makes me think it is very young. It looks to have long arms compared to the mantle with the second arm pair longer than the rest (this could also be from predation but since both L2 and R2 appear longer, I am guessing this may be a diagnostic trait). More pics if you can get them but, if I am correct in my age guess, you need to give it a place to hide most of the time and won't see it for awhile. You can keep it sequestered for feeding but make sure it can completely hide from you and the light.
thats the stock photo that ny aquitcs uses it's not what he curently has in stock, it's at least a year old. i got spider and cleatus from him and i'm prety shure they are bolth a .aculeatus but i have read of others geting nocturnal species from him, mabie it was the one in that pic. when i went to get mine he had 4 or 5 in stock all looked to be the same species and ranged in size from 4-5inch total spread(spider) up to 10inch total spread so i think the chances of geting an aculeatus are good but they are not all babbies.