Please visit our Sponsors
FAQs about Marine Crab (Including some Anomurans) Identification 22

Related Articles: Crabs, Hermit Crabs,

Related FAQs: SW Crab Identification 1, SW Crab ID 2, SW Crab ID 3, SW Crab ID 4, SW Crab ID 5, SW 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 Disease, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating Shrimp, Crustacean Identification, Crustacean Selection, Crustacean Behavior, Crustacean Compatibility, Crustacean Systems, Crustacean Feeding, Crustacean Disease, Crustacean Reproduction,

Hairy crab in my refugium      12/7/18
<Hello Kim>
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:
https://www.sealifebase.ca/summary/Pilumnus-sayi.html >
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 much.>
[image: 20181206_154743.jpg]
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 the display?
<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 scan here:
and the 22 linked files above in the series. Bob Fenner>
Thanks in advance


Tiny hitchhiker crab       3/8/18
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     5/16/17
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     1/14/17
<Hey Daniel>
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 circumstances>
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>
Thank you!
<And you for sharing. Bob Fenner>


Crab ID        11/13/16
<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.
Bob Fenner>
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.

cropped, spiffed...

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>
Edwin Lee
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!
<Hey Suse!>
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 trust.
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 harm>
Thank you for all you do!
<Certainly welcome. Thank you for sharing. Bob Fenner>

Saltwater Crab ID    3/7/16
Hi there!
I purchased a Seriatopora coral, and this cool looking fella came with! Is he some sort of tetralia or not a good 'un?
<May be>
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>
Lewis McDonald

marine crabs; ID, HI       1/22/16
Aloha crew,
My name is Michelle Nason. I am a student at University of Hawaii Hilo. I might add the reason I am here is Mr. Fenner is my hero. Never hurts to ass kiss a bit hehe ( I have met him a couple times and he might like that statement.) In all reality  I really do look up to him and after meeting him I decided I wanted to become a marine Science major.
<With a minor in business I hope/trust>

My question is this I have four crabs I need to I.D and I am having a hard time finding them. All I have is the pictures I took wen we had our lab on osmoregulation. It is extra credit for me. I was wondering is you had any suggestions as to a good source to look.
<Where are these crabs from? Do you have good pix?>
I have look through all of the crab questions that I can find and do not see anything that looks like mine. Thank you very much for your help.
Michelle Nason
<Be chatting. Bob Fenner>
Re: marine crabs      1/23/16

They are all from the Hilo side I believe Hilo bay but not sure, definitely the Big Island.
<Ahh! Still own prop. there... had hoped to be living west-side long by now>
The last two are the same lil man, none of them had any noticeable hair on legs or body. And I am sure they change as they get older or maybe they are older I just really do not know. I have searched the schools data bank and nothing. I have done search of crabs, inverts, hitchhiker, crustaceans, true crab etc. the ones I can find that look similar have no names to them
(Google pics). Thank you so very much for your help
<Mmm; well; rather than listing, pointing you to various in-print ref.s; am looking at the Stender's fab website. Looks like numbers four and five are the Xanthid: Lophozozymus pulchellus
Three may be the Laysan Crab; Tweedieia laysani
Image 2.... def. a Xanthid; though the carapace overgrown w/ algae et al.... may be Etisus splendidus
Their site URL:
Bob Fenner>

2 3 4 5
Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: