Reef safe Crab friend or foe?

Crab friend or foe?

I started my reef just over six months ago. Part of the fun is looking for new creatures to emerge.

Well I found one and was hoping you could help me identify it. It is a very small crab{at least for now}. Black with white legs.

The body is wider at the face then tapers toward the back. It seems to be feeding off the live rock {algae & such}. I have another like this one that hitched a ride with a Trumpet Coral. They seem harmless but I thought I would check with someone with a bit more experience.

Incidently the tank is doing very well. I had fresh water before this and other than adding salt, maintainance has been about the same. Thanks

Without a picture its hard to say for sure, it sounds harmless. From my experience most of the crabs that can cause damage in the reef are either Large hermit crabs, I ve seen these open clams They have a voracious appitite. Shell dia 2.5" +
OR
Small "rock"crabs - These have the pointed body shape like the blue crabs we eat. Please see page 81 of Simplified Reefkeeping

This type of crab has the "points" on the right and left side of the body as well as posing on the front. From my experience if the crab does not have these points its not likely to be aggressive as crabs that do.

Blue crab with points

Non pointed crab (examples of non pointed shell design)

I know this is a very generalised statement but Ive found it to be true.