Crab identification

[Lilah]

Hello all - I am new to all of this so am hoping that someone more experienced will be able to help me out!

We have a saltwater reef tank with some large chunks of live rock which have been doing very well. The fish are all fine, as is the hermit crab which we purchased along with the rock (there were two but sadly, one died).

My question is... three other crabs have now appeared. I will try to get photographs but it is quite difficult so I was hoping that a couple of descriptions might go some way to the identification!

One is about 3/4 inch across it's body, red eyes (not on stalks) and is covered in purple hair - looks almost like a tarantula - it has yellow/whiteish looking pincers at the end of his claws, very thin, almost like two fingers.

We then spotted another crab, slightly smaller than one mentioned above which is sort of grey speckled, red eyes (again not stalks). We asked at the garden centre we bought the rock from and they said it was the hermit crab which we thought had died and then he was just shedding - now this is clearly a load of rubbish; it is a totally different crab! The claws on this one look like proper crab claws - like a crab you see on the beach, not like the fingers on the hairy crab.

I do apologise - I am quite clearly more than a few steps down from novice!

So after spotting this little grey one, I peered in the tank yesterday at feeding time and there is another identical one hiding in the rock, this one though is about 1 1/2 inches across! Same red eyes, speckly grey body and paler pincers, just twice the size. They also have little yellow/white feelers at the front of their mouths (?).

So I am a bit miffed - the fish seem to be doing okay despite the invasion and the crabs have been content with eating the brine shrimp... so far!

Is it likely that more of these crabs will pop up?

The big one has not been noticed for around three months so I wonder if anymore are hiding in there?

Any advice greatly appreciated.

UPDATE - found a pic and this is def the critter. Can anyone identify? I don't just want to take them out, I would like to know what they are - do a bit of research etc.

I will have to keep looking for a pic of the furry one or persevere with trying to snap my own though is proving very difficult!

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[thincat]

Welcome to AA, Most crabs are unwanted hitchhikers to a reef tank and as they grow can become a real danger to your fish and inverts. They should be removed and if you have a sump you can put them there. Here is a Quote on how to get rid of them:
Originally Posted by Scubaman
there are easier ways to catch a crab - just find a glass and stand it up against the rockwork, then put something tasty in the bottom. Wait overnight and you should find a crab in the bottom and since the sides are smooth and they can't swim, it won't be able to get out. Way less of a headache than the methods you're all describing, plus the crab will be unharmed and can be put to good use in the sump or fuge.

[roka64]

I agree,
Most crabs that are hairy with pointed claws (black/brown/dark points) are usually not safe and will dine on fish and inverts if (when) they catch them.
Since your tank is new, here is a link that may help you to ID some of the critters that will start appearing:
Xtalreef

Oh yeah, welcome to the site!