i'd love to upload a picture but unfortunately the little b*gger wont pose for me. he moves pretty quick hiding in all the crevices. i've tried using the books i have to identify him but nothing really looks like him (or her) to describe i would say it looks like a standard crab. claws are proportional as are legs and body. he is very dark, black almost, but the legs have a bit of a brown stripe in them, maybe two or three per leg, although the main claws seem to be a solid black. there are also hairs on the legs. hope that describes it well enough. i'm slightly concerned at the growth rate of this one though. i remember seeing one of it's claws sticking out of a hole in my live rock and it looked like a very small brown worm at the time. now maybe 4 or 5 weeks later the claw size (coz thats all i usually see) is nearly 5 or 6 times bigger. it's body size which i saw today briefly would be the size of a £1 coin or so, but a bit deeper.
now i've lost a starfish, 1 leg a night until basically a stump was left, which i'm certain is down to this crab. the rest of my tanks inhabitants are 2 x clown fish, a blue legged hermit crab, and just 1 cleaner shrimp (there were 2 and 1 x fire shrimp but these have died over the last10 days which i don't know if that is just coincidence or down to the crab)
any help or recommendations on what i should do with it would be greatly appreciated.