FAQs about Marine Crab (Including some Anomurans)
Related Articles: Crabs, Hermit
Related FAQs: SW Crab Identification 1, SW Crab ID 2, SW Crab ID 3, SW Crab ID 4,
SW Crab ID 5,
Crab ID 6, Marine Crab ID 7,
Marine Crab ID 8, Marine Crab ID 9, Marine
Crab ID 10, Marine
Crab ID 11, Marine
Crab ID 12, SW Crab ID 13,
SW Crab ID 14, SW Crab ID 15, SW
Crab ID 16, SW Crab ID 17,
SW Crab ID 18, SW Crab ID 19,
SW Crab ID 20,
SW Crab ID 21,
& Marine Invertebrate
identification, Marine Crabs
1, Marine Crabs
2, Marine Crabs 3, Marine Crabs 4, & Crab Behavior, Marine Crab
Selection, Marine Crab
Compatibility, Marine Crab
Systems, Marine Crab
Feeding, Marine Crab
Reproduction, Marine Crab
Amphipods, Copepods, Mysids, Hermit
Banded Coral Shrimp,
Anemone Eating Shrimp,
Systems, Crustacean Feeding,
Hairy crab in my refugium 12/7/18
I found this little hitch hiker crab in my HOB refugium today. I'm assuming he's
a "bad" crab since he's hairy, but I wasn't sure how bad...
<Hmm... depends on how you define "bad." Just about all crabs have at least some
capacity to be destructive, even if just by virtue of roaming about, knocking
things over. There are many, many species of crab which appear "hairy" and they
are not all of the same genus or even of the same family.>
moment he's about the size of a nickel. Can you ID it?
<I can ball park it. It looks like something in the Pilumnidae family and within
the pilumnus genus.>
If it helps, the live rock was from Florida.
<Oh!! In that case, I think it must/might be pilumnus sayi or "spineback hairy
crab." See here:
One forum member said it was a Xanthidae crab but that seems to cover a pretty
broad category of crabs.
<Xanthoidea is a "superfamily." Thus, such a label does not narrow the ID down
The display tank is a FOWLR with no fish yet, just cucumbers, hermits, snails,
and one sea urchin that hitch hiked in. It sounds like there's a few mantis or
snapping shrimp of some sort that hitch hiked in as well but I haven't been able
to catch any yet with my pest trap (only caught one hermit crab 2x in one night
when the trap wasn't even baited).
<Haha! Good luck!>
How much damage would this guy do in the display tank?
<Hard to say - depends on how big s/he gets!>
Is it safe to leave him in my HOB refugium, or would I risk him making it into
<If he gets hungry/restless, he might it out and into the display.>
If I left him in my refugium (or maybe moved him down to my sump), would he
wreck my pod population?
<I don't think so, but these sorts of crabs tend to be opportunistic
predators/scavengers. So, if there isn't anything else to eat...maybe.>
He's such a cool little dude I'd hate to get rid of him...
<So keep him - feed him. Or, set up a separate system for him.>
But since I have a goby, a few wrasses, and a mandarin on my eventual stock list
I need all the pod generation capability I can get!
<Cheers! - Sara/Sihaya>
Crab ID please 3/19/18
Hi, I’ve been trying to catch this little crab for a few week now and last night
finally caught it and it now lives in my sump. Can any of you help ID it for me
please. It’s only small, about the size of my finger nail on my little finger.
<Umm; can't make out much here. Need a much better resolved pic. Let's have you
and the 22 linked files above in the series. Bob Fenner>
Thanks in advance
Tiny hitchhiker crab
I've been unable to find anything on this, so I'm hoping you can help. I had an
Acro frag that wasn't growing and coloring up as it should have. On closer
inspection I found a small area near the base where the skeleton was
exposed. Fearing AEFW I used a jewelry magnifying glass to look for worms and
eggs and found a VERY tiny little crab. It was probably 2-3mm including legs.
It had a black body and transparent legs. I don't have any photos.. I cut off
the tip and did a Bayer dip. I've inspected all my other frags and haven't found
anymore, but want a little peace of mind by knowing what that
guy was and if I should be worried about finding more.
<Mmm; would need a well-resolved pic to try to identify. I would leave this
little Decapod where it is. Not likely a mal-influence here. Bob Fenner>
Can you help me identify this crab like fellow
It was found in the bay area in Bonita Florida, by the gulf in Southwest
Florida, I have spent hours trying to research this to no avail. Thanks
much. Colleen Bolger
<... Might be a long/er range contaminant/recruit. I don't recognize this
decapod either. Am out dive traveling and back tomorrow where my in-print
references are. Will look for then. Bob Fenner>
<I do think this is Aratus pisonii. BobF>
Having trouble identifying this Acro hitchhiking crab
I recently bought a small Acro colony and it had 3 crabs.
<Neat! Evidence of good handling>
I knew there was one in the colony, it's part of why I chose it. But I
didn't expect 3! This album contains the pictures I'm referencing, feel free
to host them on your site though https://imgur.com/a/5b3LK I was able to
identify the small one (3rd & 4th pictures) as a Hairy blue-eyed Acro crab
(Cymo andreossyi) which as I understand it will pick on
<All will/do to extents. I'd keep them all... not that damaging in most
On large colonies they're supposedly symbiotic, but dangerous to small
colonies, so I tossed him in with my P. ciliata mantis shrimp. I was able to
identify the other (last picture) as a Tetralia crab, safe and symbiotic,
and put it in the tank with the coral. But I'm stuck on the one pictured in
the 1st and 3rd pictures. The color matches the coral closely, and the body
shape reminds me of a Trapezia which makes me think that it's commensal.
<I agree on both counts>
It's legs are a little bit fuzzy though. One claw is slightly larger and a
little bit sharper, the other is smaller and has flat tips, clearly intended
for gripping and scraping. I've been Googling for a couple hours now and
haven't been able to get a good ID on him. In the meantime he's in a critter
keeper with an airstone. So, should I put him with the colony
or would it be wiser to let him test his fate with the mantis?
<As stated, I'd keep all>
<And you for sharing. Bob Fenner>
<Your uncropped pix are too poorly resolved for use. See, and in READ on WWM
re our image requirements, AND review the many FAQs files on Crab Id.
Hi need help on identifying a crab I found from a live rock. currently in my
sump but if it's reef safe I will put it into the main tank.
Re: Crab ID 11/14/16
Apologies hope these 2 cropped pix help .
<Nope; still poorly resolved, don't show diagnostic characters. READ where
you were referred to on WWM. B>
Re: Crab ID 11/14/16
Did my reading and I am leaning 30% its a Xanthid
<I tentatively agree... are the tips of the claws darkened?>
(stays in sump) and 70% its a Ruby Red Crab (could be added to tank) ?
<I'd leave it out of the main/display... Yes to keeping it in the sump.
Re: Crab ID 11/15/16
No the claw tips are white. been in my sump for 2 weeks and survived ?
<As long as dissimilar... a Xanthid trait>
Could it be a box crab - they are reef safe aren't they. I have a full soft
coral tank so the risk of a Xanthid causing destruction is lower ?
<Oh yes; SEE/READ on WWM. Don't write: read. B>
Possible Xanthid Crab? 5/22/16
Good evening Bob and Company!
Thank you so much for your fabulous website; you are an amazing resource.
<Glad to share>
I keep a 60 gallon seahorse and soft coral reef (primarily sun corals and
assorted sea fans) and always acquire all of my livestock (aside from the
seahorses, which come directly from the breeder) from a single local shop that I
Tonight I brought home a piece of live rock with mixed colonies of clove and
daisy polyps (it’s lovely) - but about an hour after introducing it to the tank,
I noticed it “breathing” - which, of course, neither of these species do. A
brief investigation with a flashlight and a pair of long tweezers revealed this
little guy hiding beneath the polyps. (Photos attached.)
<I see this Decapod>
His legs are much hairier than they appear in the photos - like the legs of a
Mithrax crab (but his pincers are clearly wrong for Mithrax).
I pulled the rock from the tank at once, nudged the crab into a bowl, and shot
these photos. After spending about an hour on your site, I suspect he’s a
Xanthid - and that it’s a good thing I removed him before he could cause any
havoc. Can you confirm his species, or at least let me know if I should keep him
away from the seahorse reef?
<It is a member of this family; and I would keep it out of your seahorse system>
(My husband thinks he’s cute, but I don’t think my softies and seahorses will
appreciate this particular variety of cuteness.)
<Mmm; if you have a live sump; I might place this crab there; where it can do no
Thank you for all you do!
<Certainly welcome. Thank you for sharing. Bob Fenner>
Saltwater Crab ID 3/7/16
I purchased a Seriatopora coral, and this cool looking fella came with! Is he
some sort of tetralia or not a good 'un?
I have looked all over but Tetralia matches him.
<Am out dive-adventuring in Roatan; away from my ref. materials. Looks to be a
Xanthid. Use your search tools to look up pix of this family from the geog. area
your coral was collected. Bob Fenner>