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FAQs about Marine Crab (Including some Anomurans) Identification 15

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, SW Crab ID 22, & 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,

Whoa big boy!

Crab Identification 9/11/09
I have been unable to identify these crabs; and was hoping you may be able to help. They were collected in the northeast US in approximately 30 feet of water. The largest of the three is a little larger than an inch. A similar crab I was able to find on the internet was Cryptolithodes typicus.
<If it were Cryptolithodes typicus, they would be a long way from home.
Butterfly crabs are generally found in East Pacific waters.
I have no idea what type crabs these are. There are hundreds/thousands of species of crabs
<<... No... there are about 5k described species of "crabs" of which about 500 are "false crabs", Anomurans, like the Hermits... RMF>>
and researching to accurately ID would be much too time consuming. As we are all volunteers with little time available,
our time is focused toward animals generally encountered in the tropical/sub-tropical
marine hobby. Now, if they were from tropical waters, an ID may be possible. Time spent Googling would be your best bet, is what we would need to do.>
Thank you for your time,
<You're welcome. James (Salty Dog)>
<<James, again, please don't respond to queries for which you don't have a qualified opinion. RMF who doesn't know what these are either. Am going to put in LynnZ's in-box>>

Re: Crab Identification
Good morning Bob,
Mmm, does the "hundreds/thousands" not fall into the "5k described species"?
<Mmm, perhaps I misread... as hundreds of thousands. Sorry re>
Not being a smarty pants here either, just thought I was in the ball park. You are correct Bob, I'm not qualified to ID crabs, especially species not related to the hobby. Was just trying to point out that we are not a research site as such, but a knowledge base for subjects associated with the tropical marine keeping hobby.
If I'm on the wrong track here, please do let me know.
<Thank you, BobF>

Re Crab Identification 9/15/09
Thanks for passing the pictures along for id. I don't know if it would help but the crabs were collected in Nantucket Sound (south of Cape Cod). The crabs are currently at The Cape Cod Museum of Natural History, they have yet to identify them.
They don't seem to want to feed, and I was wondering if you had any suggestions for what to give them.
<I haven't a clue, especially not knowing what they are. Likely specialized feeders.>
Also I thought you might have the name of a person or group I could contact who would specialize in crabs that are not tropical.
<I know of no one, Bob or other crewmembers may know. May want to ask the folks at Cape Cod Museum Of Natural History.>
Thanks again for your time,
<You're welcome. Sorry we could not be of more help. James (Salty Dog)>

Re: Crab Identification: Likely Elbow Crab -- 9/22/09
<Hello Cam, Lynn here today with a follow-up.>
I have been unable to identify these crabs; and was hoping you may be able to help.
<I'll sure try. As was noted in the previous response, there are an awful lot of crab species out there!>
They were collected in the northeast US in approximately 30 feet of water. The largest of the three is a little larger than an inch. A similar crab I was able to find on the internet was Cryptolithodes typicus.
<It is indeed similar, but I believe it's more than likely a Brachyuran/'true' crab (4 pairs of walking legs) in the family Parthenopidae. These are commonly known as 'elbow crabs'. Cryptolithodes species (family Lithodidae) are Anomurans/'false' crabs with 3 pairs of walking legs and comparatively short claw arms. From the looks of your little fellows, the term 'elbow crab' seems to fit rather nicely. There are quite a few Parthenopid species that have triangular (or near triangular) carapaces and fairly small/sometimes hidden walking legs. Here's an example (Heterocrypta lapidea): http://www.scielo.br/img/revistas/bn/v5n2/en_a03fig22.jpg . This specie's range is listed as the West Indies to Brazil so unfortunately, it's not a likely candidate. However, it appears similar enough to warrant more research in that direction (including other genera within this family) should you desire to pursue an ID. Unfortunately, I can't see quite enough detail to go any further. Here are more examples from the Central Pacific region. I know it's not the area your crabs are from but you can at least see the various attributes within multiple genera all in one location: http://decapoda.free.fr/search_result.php?faname=Parthenopidae
Parthenopidae classification including genera: http://animaldiversity.ummz.umich.edu/site/accounts/classification/Parthenopidae.html >
Thank you for your time,
<You're very welcome.>
<Take care, LynnZ>
Hi Lynn,
Went to the UofM Animal Diversity site as you list below and I did not see any pics???
Oops, I see now, one needs to click on Parent Taxa to locate the pics.

Identification problem... Small crab, SW 8/30/2009
I would like to ask your advice please.
Whilst carrying out my second 10% water change of the week, today and general cleaning routine, I noticed a tiny crab in my live rock, at first I thought it was a tiny tarantula, but then quickly realised when it
surfaced from the crevice in the rock, that it was in fact a crab. It is grazing on the live rock and is about 1 centimetre big. Taking a good picture has proved too difficult so I have tried to write a good description of it.
White/cream coloured claws, with brown equally sized pincers, with white tips to them. Pincers seem to have one serration on each pincer, half way up.
On the end of the other legs there are pink tips.
The body is cream/white in colour and there are two thick black vertical lines running through the shell of the body.
Eyes are black, not on stalks,
There are slight hairs on the legs and body. The legs are white/cream with black dots where there are joints.
It is not a hermit crab.
Could you please advise me about this crab, I have tried to catch it but it
is a fast mover, I am worried about my corals and fish:
<Mmm, at this size, not likely an issue. T'were this system mine, I'd just ignore this little Decapod>
Blue male Psychedelic Mandarin
Red female Psychedelic Mandarin
Yellow Tailed Blue Damsel
Pair of Mated True Percula Clowns
Royal Gramma
Thank you in advance.
<Innocent till evidence of guilt... Bob Fenner>

Crab Identification: Fiddler Crab -- 10/15/09
Hi :)
<Ah, bonjour Marie, Lynn here today!>
I received yesterday 2 little red crabs from the Philippines and I'm not sure what they are because of the eyes. I think they may be fiddler crabs...
<You're right. The overall shape/length of the stalked eyes and sharply pointed carapace seem to be fairly common within the semi-terrestrial fiddlers in the genus Uca, family Ocypodidae. The closest I can find is a photo of something alleged to be Uca arcuata (see this link: http://www.geocities.com/rainforest/canopy/5280/philip.htm ). Unfortunately, I can't confirm the ID. Either the color/pattern varies quite a bit (as shown at the above link) or they're different species entirely. Apparently, in the Philippines, these are mainly mangrove/shallow water/intertidal crabs that make their burrows in the mud and sand. Interestingly enough, I've seen a similar species being offered for sale on the internet, listed as a 'Red Burrowing' crab in the genus Uca. >
..even if they don't have the oversize claw... maybe they're female.
<Yes, my thought as well.>
I sent you a picture, maybe you can help me with this identification.
<I sure wish I could give you a solid ID to species level, but there are just too many possibilities and not enough available information on the 'net and within my research books.>
I don't want to give bad information to my customers.
<Good for you! I wish all merchants were this conscientious! Unfortunately, I have to add that these little crabs should not be kept in a fully submerged marine system. They'd do much better in an environment more closely resembling they're natural habitat (mixed land/water). For more information on this group of crabs, please enter the terms (Uca or fiddler) into our Google search engine (http://www.wetwebmedia.com/Googlesearch.htm). I've seen several posts regarding solid red fiddler crabs with reports of them being very reclusive. Apparently, once added, they tend to burrow/hide and not come out much. In Barnes' Invertebrate Zoology (sixth edition, pg. 717), it states that tropical species of this genus 'tend to be active only during diurnal low tides'. That's not a whole lot, even in the wild! Also, they're still crabs and basically opportunistic, so hobbyists will need to keep these well fed to discourage picking/killing of desirable livestock.>
Thank you
<It was a pleasure, Marie.>
<Take care, LynnZ>

Re: Anemone & Crab ID Query 10/9/09
Hi Bob and Crew,
I saw this query come in but unfortunately can't ID the anemone in question. As for the crab, it looks like a Xanthid of some sort but unfortunately, there's just not enough information for me to take it any
further. I don't know the crab's size, where it originated, or if it was associated with anything else. In addition, I can't quite see enough of the carapace or claws. It looks like a lot of detail (how hairy...where hairy, surface texture/bumps) is lost/obscured because the crab's out of water, with water clinging. Anyway, all I can really offer is that it's likely a Xanthid. Sorry about that...wish I could be of more help!
<Thank you Lynn... I can't tell much more myself. BobF>

I also didn't grab the query because of the crab ID, but I believe the anemone is a Long Tentacle/Corkscrew (Macrodactyla) Anemone. The picture quality is poor/dark so I'm not betting any money on it.
<Me neither. BobF>
Anemone & crab ID

Hi need an ID for this anemone. it's color is dark brown/maroon.
Thanks Siddharth
<Can't discern from this poor photograph. Bob Fenner>

Mystery Crab (actually an Anomuran) -- Likely Porcelain Crab -- 8/16/09
<Hi Sarah, Lynn here today.>
I hope you can help me identify this little guy.
<Me too!>
I've had my tank up and running a year and a half now. The last time I bought any new critters for my tank was about 3 months ago.
This morning, this little guy showed up.
<Neat! It looks like a little porcelain crab, family Porcellanidae, of which there are many genera and species. They're primarily filter feeders that rhythmically wave a pair of interesting feather/fan-like mouth parts through the water in order to gather organics, plankton, etc. Although these are referred to as crabs, they're not actually 'true' crabs (Brachyurans). They are instead Anomurans, a group that includes hermits, mole crabs, squat lobsters, etc. Both Brachyurans and Anomurans are decapod (ten-footed) crustaceans, however, crabs such as yours have 3 pairs of walking legs instead of 4. A much smaller fourth pair is folded and held either above or below the abdomen (not used for walking). They also have long antennae just distal to/behind the eyes, a mobile abdomen that can be used to propel the crab, and large claws that are used for territorial disputes and defense instead of feeding/predation. These crabs, although primarily filter feeders, are also opportunistic scavengers and detritivores. Luckily, they're generally small and don't pose anywhere near the risk that true crabs do (such as Xanthids -- family Xanthidae). I would keep this little fellow around and enjoy! As a scavenger, it'll likely take most foods -- pellet, flake, bits of meaty foods (of marine origin). For more information, please see the following links: http://www.wetwebmedia.com/galatheids.htm
Similar species, listed under 'A new porcellanid species from the Caribbean Sea': http://www.uni-giessen.de/porcellanidae/ >
Thanks again,
<It was a pleasure.>
<Take care, LynnZ>

Crab ID: Possible Xanthid or Pilumnid, Brachyuran Identification Issues -- 7/20/09
Hello Incredibly Helpful WetWeb Crew,
<Hello incredibly nice Lianne, Lynn here today.>
If possible, is there someone who might identify this crab for me? (I checked your ID pages first.)
<I sure wish I could but for me to even begin to narrow things down, I'd need some additional photos such as close-up shots of the claws (showing the tips, and inside edges), a good shot from above showing the carapace detail and all legs, as well as a shot of the underneath/ventral surface. Unfortunately, even with excellent photos, we'd be doing well to narrow it to the family level. Identifying Brachyurans/true crabs can be quite a challenge. According to an excellent study last year (See this link: http://rmbr.nus.edu.sg/rbz/biblio/s17/s17rbz.pdf ), there are 38 superfamilies, 93 families, 1271 genera and subgenera, and a whopping 6,793 valid species! That's a lot of crabs! Some are easy enough to narrow to family or genus because they have such obvious and unique features, but unfortunately there are way too many crabs left out there that look similar enough in available photos to be easily misidentified. If it were only as easy as 'hairy crab = X' or 'spatulate/spoon-tipped claws = Y'! Wouldn't that be great? As it is, the most dependable way of getting a definite crab ID is to have the fellow right there in front of you, along with a really good identification key or better yet, preserved specimens of similar crabs. That way you're able see all the pertinent little details that separate one family, one genus, one species from another -- and believe me, those details can be small. Barring that, we have to depend on photos and unfortunately not all species are available online or (at least within my) reference books. In a perfect world, we'd have online sites with up-to-date lists, dichotomous keys, and detailed photos of all the indigenous crabs from each ecosystem/locale around the world. I think we're headed that way, but for right now, it's just not out there.
By the way, please don't construe what I wrote above as some sort of dressing-down because you asked for a crab ID. Believe me, that's not my intention at all. I love seeing all the neat little crabs that people find in their tanks and enjoy the challenge of ID work. The fact is, we get crab related ID queries fairly regularly and it's frustrating to only be able to give general, instead of specific, information on most. I just wish I were an expert and could offer swift/solid ID's, along with species summaries! Anyway, enough of that - let's get back to your crab! From what I see in the photo, I'm guessing that it's likely either some sort of Xanthid (Family: Xanthidae) or a Pilumnid (Family Pilumnidae). I've seen a number of Xanthids that have one or both claws spatulate/spoon-tipped (genera: Leptodius, Phymodius/Cyclodius, Chlorodiella, Etisus, Pilodius, etc). Unfortunately though, they tend to have hairy legs but not hairy carapaces. Pilumnus spp. crabs (Family: Pilumnidae) are notoriously 'hairy' crabs (all over), but I've never seen one with spoon/spatulate claw tips. Also, they tend to have deeper bodies than what I'm seeing in your photo. That doesn't necessarily rule this family out it's just that I couldn't find any like yours. Please see the links below for examples:
Leptodius : http://www.wildsingapore.com/wildfacts/crustacea/crab/xanthidae/leptodius.htm
Cyclodius: http://decapoda.free.fr/illustration.php?n=2&sp=628
Pilumnus hirtellus: http://www.klissurov.dir.bg/black_sea/crustaceans/big/PilumnusHirtellus04.jpg
Pilumnus spinosissimus: http://www.scielo.br/img/revistas/bn/v5n2/en_a03fig44.jpg >
He is dead, as you can see here,
<Well, based on the fact that the eyes look empty behind a thin shell/covering, I'm wondering if that isn't just a shed from a recent molt? If you still have the 'body', flip it over and take a look underneath. Is the abdomen opened up? If so, can you see any of the crab's 'innards' or is the shell empty? If it's empty, then the crab has recently molted and will be in hiding until his shell hardens.>
..but I still have a tiny one (1/3") in residence, who also hitchhiked into my reef tank on Vanuatu live rock. His carapace measures 5/8" across and his total width is about 1.25." His pincer claws are the forceps style of a Mithrax forceps crab, with only the tip of the pincer flattened, but he is hairy on all but the pincer itself and looks quite different to my eye.
<Heee! Don't get me started again! The good news is that in lieu of us knowing which species you have, we can at least derive some information from the claws. It's one of those 'form follows function' issues. Flattened or spoon-like tips are excellent for scraping algae, etc., off hard surfaces, grasping filamentous algae, and for scooping up soft materials. These crabs tend to be a bit better risk in reef tanks, but they're still omnivores and opportunists. They're generally pretty well-behaved when small, but can be a problem later on as their bodies and appetites grow.>
I observed him shyly clipping and consuming the algae on my live rock over several months.
<Yep, that fits.>
I attempted to get him interested in meaty stuff to be able to trap him, but no go. Then found him dead this morning.
<He may be in hiding. If it was just a molt, he should be back out in a couple of days.>
His body appears to be completely unscathed, but perhaps he duked it out with my newly-out-of-quarantine Leopard Wrasse?
<Probably not. Any attack resulting in death would have been pretty obvious - dismemberment and/or nipped/missing appendages and parts(like the eyes)>
(The only other tank occupants: two young percula clowns, a young yellow-tail Damsel, two cleaner, two ghost, and one fire shrimp).
<Doubt any of those could have done it -- unless the crab was in a molt and exposed/not hidden. If that had happened, there would have been obvious damage to the body as mentioned above. I'm thinking that unless you can actually see tissue inside that shell, there's a good possibility that what you have is just a shed.>
Thank you for your thoughts
<You're welcome! Bet you weren't thinking you'd get quite so many of my thoughts though, huh?>
..and your phenomenally helpful web column.
<On behalf of Bob and the crew past and present, you're very welcome!>
<Take care, LynnZ>
PS. He has 4 legs on each side in addition to his pincers.

Re: Crab ID: Possible Xanthid or Pilumnid, Brachyuran Identification Issues -- 7/21/09
<Hi Lianne!>
Thank you so very much, Lynn, for your thoughtful and informative answer.
<You're very welcome.>
I simply had no idea of the complexity of the species
<It's easy to see how someone could devote a good portion of their life towards identifying and classifying these guys!>
...(or would it be family: I get confused with the names for different levels of scientific differentiation between animals?).
<I know what you mean. Here's the order (from least to most specific): kingdom > phylum > class > order > family > genus > species. Frequently, prefixes like super, sub, infra, etc., are added to create sub or superior categories. In the case of true crabs, it's order: Decapoda, infraorder: Brachyura, then on to superfamily, family, genus, and finally: species.>
It's wonderful to have you open that door; I will begin doing some research and will let you know if I discover similarities.
<Please do!>
It was great to be pointed in a direction!
<I'm glad I was able to help. Hopefully you'll enjoy the subject as much as I have. I just find crabs to be fascinating little creatures. Just the variation in appearance alone is amazing. They range from the truly bizarre and outlandish to the most simplistic - almost generic, to the near comical or cartoon-like. All are wonderful!>
<Take care, LynnZ>

Help Identify a Crab: Possible Xanthid: Paractaea monodi - 8/22/09
<Hello Susan, Lynn here today.>
Have you ever seen this crab before?
<Oh yes. I've seen this little crab before - or at least those like it. My best guess is that it's most likely a Xanthid in the genus Paractaea, possibly a fairly cosmopolitan species: Paractaea monodi (Monod's round crab). Please see the following links for comparison:
See several photos half-way down the following page and another good one at the bottom: http://www.ivanov.ch/redseaMax/crabes.html . By the way, there are also some 'red-eyed reef crabs' in the genus Eriphia (family Menippidae) that look similar, but the carapace is not quite right (spiny/serrated edges instead of smooth, different overall shape and surface anatomy, etc.). See examples here: http://www.wildsingapore.com/wildfacts/crustacea/crab/eriphiidae/ferox.htm >
I have looked at many pages of crab pictures today and I cannot find one like it.
<Well, there are an awful lot of crab species out there!>
This crab was not purchased on purpose- it was apparently living in a piece of live rock that was added to the tank!
<Yep, that's usually how they're introduced!>
The shell is a very deep purple/black color under the lights and its eyes are dark orange/red.
<It's actually a very attractive little crab, but an opportunistic omnivore and scavenger as well, with an unfortunate potential to destroy livestock.>
Any leads to identifying it would be appreciated.
<Hope the above information helps!>
<You're very welcome.>
<Take care, LynnZ>

Hitchhiker Crab/ID 8/13/09
Can you tell me what type of crab this is and whether or not I should keep it in my reef tank? I have looked all over and can't identify it.
<I did a quick check with a 100 or so photos I have and cannot come up with an ID. Let see, that leaves about 749,900 crabs I have not saw:)
The crab does appear to be a specie of a swimming crab (last pair of legs appear to be swim paddles), and most are very predatorial. To be on the safe side, I would remove.>
<You're welcome. James (Salty Dog)>

Crab ID -- 7/24/09
<Hello there!>
I am hoping you can assist with the identification of a crab I have had in my tank for approximately a year. It started out about ½" across but now has grown to well over 1". I have not seen him in over 6 months and then there he was tonight. I looked through all the available photos but did not see anything that I could be sure about. I can speculate that he came in on some rock from Florida.
<Unfortunately, I can't see enough of the little fellow to be able to give you much in the way of an ID. All I can say is that it looks a bit like a Pilumnid (superfamily Xanthoidea, family Pilumnidae). Please see the following links for examples of crabs in this family for comparison: http://www.scielo.br/img/revistas/bn/v5n2/en_a03fig44.jpg
Pilumnus sayi: http://www.dnr.sc.gov/marine/sertc/images/photo%20gallery/Pilumnus%20sayi.jpg
Just bear in mind that all crabs are opportunistic omnivores that are usually okay when small, but can be a problem as their bodies and appetites grow. If (and that's a really big if) what you have is indeed something in the genus Pilumnus, those usually stay fairly small. The same rules still apply though -- if the crab gets hungry enough, it can cause problems.>
I am wondering if I should (attempt) to remove him from the tank.
<If the opportunity comes along (he's out where you can net him) I'd remove him and find him another home. I wouldn't go so far as tearing the tank apart to find him though. If you're unable to get him out, I'd make sure he's got enough food to discourage him from sampling something he shouldn't and keep an eye on him (and your livestock). He may be getting a bit more bold because he's hungry. You could try feeding him meaty bits of marine origin (shrimp/fish/clam etc), sinking pellets or the like. Obviously, if you're noticing any damage to your livestock, I'd recommend getting him out of there sooner rather than later. You can always try to trap the little guy. There are some commercially available versions on the market or you could try the tipped jar method. Once you figure out where he hangs out within the rock, take a clean jar and lean/wedge it up against the area. Put a piece of stinky shrimp or bait in the bottom and wait. You might have to leave it in place overnight. The idea is that the crab smells the bait, falls into the jar and can't climb back out. Sometimes this works, sometimes you end up with everything but the crab in there! Hopefully your little crab will be bold enough to come out in the open where you can net him without any fuss!>
I have noticed that starfish that I have added will get injuries that appear as if the insides are exploding out from them and I wonder if he might be causing them.
<Yikes. It could be but it could also be that the star is dying/reacting to adverse water conditions, rough treatment prior to (recent) purchase or any number of things. If it happens again, do write us with all pertinent info -- water parameters, what species it is, what other livestock you have, how long you've had it, etc.>
Thank you!
<You're very welcome! Take care, LynnZ>

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