Friend or Foe: another crab ID

[jayelblock]

Found this guy on a new box o' rocks I just received. Smaller than a dime...
Friend, or foe?

http://farm5.static.flickr.com/4110/5100357075_bc6cc3fae8_b.jpg

[VacavilleFC3S]

looks like some form of sally light foot crab, there pretty destructive and extremely fast. you can toss him in the sump for a bit, i've never liked them

[jayelblock]

Thanks. I did look through all the i.d. guides before I posted, but of course, there are a thousand different kinds of crabs.

I thought the elongated body looked like some kind of mithrax crab, but who knows...

[Basketstar]

Looks more like a mithrax to me. Are the claws pointed or spade shaped?

[jayelblock]

Claw tips are pointy, I think, but they are so teeny and light colored that I can't tell.

[BEASTIEPENDENT]

No similarity to Mithrax or Mithraculus, sorry. It does look like a Pachygrapsus sp., most probably it is Pachygrapsus minutus (Milne-Edwards, 1873). Can You determine where the live rocks came from?

Pachygrapsus are predators of everything that is smaller than themselves. It depends on what else You have in Your tank if it is "friend or foe". It probably won't harm corals. On the other hand it would be good if the crab had a possibility to get above the water, they like to get some air.

[jayelblock]

Can You determine where the live rocks came from?

The rock is Indonesian, purchased from Vivid. It makes sense that this crab likes some air--he was running around the bottom of the box when I unpacked the rock, and didn't seem too distressed by being out of water. I threw him back in with the rock, which is curing, so I could probably trap him again if necessary. The ammonia and nitrites were fairly high as of this morning, so it's not the most wholesome environment.

Definitely foe, since the rock is intended for a nano with a tiny red headed goby.

thanks for the info

[BEASTIEPENDENT]

That fits. This species has a very wide distribution but Indonesia fits perfectly. Though the picture has no great depth of field some small details are clearly identifiably (front, exorbital tooth, carapace shape, claw spines, setae). Together with the location I would say: we have him. ;)

These crabs live in the intertidal zone, where it is wet all the time but they don't have to be submerged all the time. Usually they search algae for small crustaceans and feed on some of the algae itself either. They are very (!) fast and have good sight. Their flat body is built to keep them on the rock in the surf and waves but helps them to hide in small crevices too.

[jayelblock]

Outstanding! Thanks so much for your authoritative i.d. I could have looked through taxonomy resources for a month and never found it.

I'll provide some rock which reaches the surface and see if he comes out to bask.

[BEASTIEPENDENT]

You're welcome. I'm glad You keep him and don't flush him away. :-)

You're free to share Your observations as user comment on http://www.reeflex.net/tiere/3009_Pachygrapsus_minutus%20(Milne-Edwards,%201873).htm