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FAQs about Marine Crab Identification 10

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 6, Marine Crab ID 7, Marine Crab ID 8, Marine Crab ID 9Marine Crab ID 11, Marine Crab ID 12, SW Crab ID 13, 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 identificationMarine Crabs 1, Marine Crabs 2Marine 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,

Re: Another questions :) ATTN Mitch... crab ID, WWM Crewmember gender/name mis-ID    6/10/08 Hi Mitch, <Hi Patrick,> While I was pursuing the aiptasia tonight (got a good start) <Congrats.> I noticed a little green crab in my turtle grass, then I noticed there are 2... <perhaps a breeding pair.> I don't know how I missed these guys. <Easily done.> They aren't emeralds, <No they are not.> Looked all over WWM can't find any that look like these, although I did see a post about a crab a guy found in his turtle grass and you guys weren't sure what it was... <Sorry, I'm not too much help here. It is a very distinctive crab, and I thought I might be able to find more information for you. From the images it does appear to be a very pretty shade of green, which I thought would be most helpful in the identification. I also thought the turtle grass might be a clue as well but I didn't have any luck searching along that route either. I'm at a loss. Your crabs appear a little more refined and sort of remind me of some commensal crabs found in association with some corals, but most crabs are opportunistic omnivores and are not to be trusted. You might want to isolate these guys in a sump so they don't cause trouble. More info here: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm and related links in blue and here: http://www.chucksaddiction.com/hitchcrabs.html Michelle>

Re: Another questions :) ATTN Mitch... crab ID     6/23/08 Thanks Michelle, <Welcome Patrick, sorry for the long delay. I was hoping to come up with an ID for you, but didn't make much progress, sorry.> I was leaning towards some sort of porcelain crab but after watching them for a while last night I was able to see that they have 4 legs on each side in addition to their claws so they are true crabs. Also I noticed that the very tips of the claw has white on them. If you guys don't know what they are they must be very uncommon. <No, not necessarily, but not something I am familiar with.> Not sure what to do with them, they never seem to leave their turtle grass home and as I was watching them last night, they seem to be filter feeding, <It is possible.> they climb up the grass, push it apart and you can see their mouth parts going a mile a minute. <I would likely allow them to stay in place.> I had one of the turtle grasses in the sump for a while, it didn't like it there, probably because of the crappy light 4700K compact fluor bulb I have down there... It turned yellow, <Mmm, sounds like it wasn't getting enough nutrients, may have been more a sandbed issue than a lighting issue, Thalassia prefers a deep, enriched, substrate, 3-4 inches minimum, for optimum growth and development, thought the grass would prefer closer to daylight lighting, ie 10,000K.> I moved it to the main tank and it started growing like crazy! <Better conditions for it. Good luck with these little guys. I would just keep an eye on them. Cheers, Mich>

Please could you ID this crab: Likely Xanthid - 6/7/08 Hi, <Hi Ranjith, Lynn here today.> I found this fellow in my 5 month old tank. <Okay> Couple of observations in the tank (might be or not because of him). 1. Found empty shells of similar but small crab (maybe this one moulted?) <Either that, or there are multiple crabs present.> I observed this over last 2-3 months. From the last 2 weeks he is active and is seen around the tank. 2. Found a piece of my moon coral torn off. <Ouch!> I saw him trying to burrow under the moon coral once a week or so ago but he left the place in some time. He does not go there as far as I have observed but maybe when it's dark?? Yesterday night I found a small 2cm piece of the moon coral not far from the coral itself. <Mmmm, not good.> Other inhabitants are: 1. Flame angel 2. Bicolor blenny 3. Skunk clowns Tank is 120 gal bowfront Would you need more info to ID this crab? <Unfortunately, there are so many possibilities that without having the crab directly in front of me and knowing where it's from, the best I can do is ID it to one of two families. The first is Cancridae. These are also called 'Rock crabs' and often have fluted, toothed, or scalloped carapace edges. I can't quite tell in the photograph if your crab has this feature or not. It actually looks rather smooth to me, so if that's the case then it's more than likely something in the family Xanthidae. Xanthids, ('Mud' crabs) are common hitchhikers and are unfortunately some of the more notorious crabs as far as their potential for being destructive. Some are coral commensals, and relatively innocuous, but all are omnivorous with the potential to cause problems. That goes for crabs in the family Cancridae as well. I would recommend either trapping and relocating this crab, or keeping it well fed in hopes of discouraging it from sampling your desirable livestock. If it were me, I'd relocate it. For more information, please see the following links: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm http://www.chucksaddiction.com/hitchcrabs.html http://en.wikipedia.org/wiki/Cancridae Cheers and Thanks Again <You're very welcome! Take care, -Lynn>

Small crab in brain coral 5/13/08 First off, let me say this is the greatest site I've ever stumbled upon and you've answered many of my questions about my reef tank. Now, here's my situation: I bought a colored brain coral this weekend. The coral has been inflating and deflating throughout the day, and it has eaten but today I noticed a spot that I thought was tissue recession. After observing it all day, I saw that it is a tiny (I mean really tiny) crab living inside it. It has eaten a tunnel out of the coral. <It is a coral-gall crab or gall crab... very interesting creatures.> I tried to remove it with tweezers and I thought I killed it, but it just backs up into the coral and I can't get it. I don't want to lose this coral, but I really don't want the crab to migrate to my pride and joy bubble coral, or any of my other LPS. Do you think this crab will eat the coral its in? <No worries, they are harmless and don't appear to reproduce in captivity (or, if they do, not enough that anyone has ever reported a problem with them). I myself have had both a male and a female in my tank. The female even had eggs at one point. But I never noticed any babies (nor any new crabs).> Is there any way I can flush it out? I really want it gone. <Aww, please consider letting the little guy live. They're not harmful and are actually quite interesting little creatures. Some people say they never leave their holes, but I have this picture I think "proves" otherwise. Please pay no mind to the state of the coral they're on... that was not at all their fault, I had accidently dropped the coral in a bucket of vinegar (actually, come to think of it maybe that's why the crab came out of the hole). lol That's NOT a suggestion!! ...certainly did more harm the coral than to the crab! ::sigh:: Sara M.>

Black Crab ID: Start With WWM Sources - 4/21/08 <Hello> Need help ID'ing a stowaway on a Tonga live rock. I haven't gotten a clear shot of it, he's pretty shy. It's a dime sized crab, all black, with a pattern of white lines on its back. It has not left the rock it lives in, and when I do see him, he quickly hides. <Typical> I'll send a pic as soon as I catch him. <Sounds good. Best case scenario would include detailed photos from above, beneath, and face-on. Even then, identifying crabs to the species level can be very difficult indeed. However, with enough information we should be able to narrow it to a basic group. In the meantime, please read through the information and compare the photos at WWM regarding crabs. Start at this link, and be sure to go through the associated links at the top as well: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm Take care, -Lynn>

Tiny White Crab on Montipora capricornis: Gall crab - 4/8/08 Hey all. <Hi Andy> I have a Montipora capricornis on which I found a tiny white crab (I think). When I noticed it this morning, I thought it was simply a piece of debris hanging off the coral, but tonight with the lights out and a focused flashlight I was able to see that it was in fact some type of animal. I was able to suck it off with a turkey baster. It is very tiny, so without a magnifying glass I can't make out its features very well, but it does have at least 4 legs on each side. <Thanks, that's an important bit to know when identifying crabs!> The best way I can describe it is to tell you it looks like a white deer tick. <Oh man, do I ever despise ticks! They're creepy little bloodsuckers!> I have attached pictures--I hope you can make it out. <Unfortunately, I can't see enough to differentiate between the two crab families I have in mind. However, I'm hoping that the photo links I'll list below will help you determine which one it really is.> I searched around on WWM to see if anything popped up on this subject that might give me an ID, but I came up empty handed. I note that the flesh of the coral at which this crab was attached all day is totally undamaged, so I'm thinking (and hoping) that it is not a threat <Not likely, no. Most are small commensals.> (although I disposed of the crab anyway). However, there is a tiny, round hole in the structure of the coral that is under the place this crab was attached and that looks like it has been there a while (see pic--maybe the crab was living in this hole?). <Very likely, yes.> Any thoughts on what this crab might be? <It looks like something either in the family Cryptochiridae (coral pit/gall crabs -- many genera) or the family Xanthidae (genus Cymo - gall crabs). I've never heard of these crabs inhabiting Montipora corals before, but considering how little I really know and how much I still need to learn about them, that doesn't mean a whole lot! One thing that's going to help that I can't see in the photos relates to the claws. If those on your crab were easily seen and fairly robust, possibly dark tipped, then it's likely a Cymo sp (xanthid). If, however, your crab had barely noticeable, slender claws, then it's likely a Cryptochirid. The crabs in this last family look more like ticks to me, but take a look and see what you think (the first two are Cryptochirids): Hapalocarcinus: http://cookislands.bishopmuseum.org/species.asp?id=7372 Cryptochirus: http://cookislands.bishopmuseum.org/species.asp?id=7200 Cymo: http://decapoda.free.fr/illustration.php?n=3&sp=212 > As always, thanks for your help/time. Andy <You're most welcome. Take care, -Lynn>

Re: Tiny White Crab on Montipora capricornis: Gall crab - 4/8/08 Lynn, <Hi Andy> Thank you for the response. <You're most welcome.> Hmmm, hard to tell. The claws definitely were NOT noticeable. In fact, I couldn't see them at all--the only things I could see were the 4 legs on each side. It resembles the Cryptochirid, but doesn't look like an exact match. <It may be something else within the Cryptochiridae family. Unfortunately, those were the only two online examples I could find of the different genera within that family. Depending on where you look, there are anywhere between 6 to 20 different genera and beyond that, a whole slew of species so there are lots of possibilities.> I'm just glad it likely was not harmful to the coral. <Me too!> The marine world is a strange and fascinating one. <It is indeed! Take care, -Lynn>

Sea Apple Hitchhiker: Pea Crab - 3/21/08 Hi, <Hi there Joe> I am researching this for someone and I haven't been able to get an answer as of yet, I was hoping someone here could help me. <Hope so!> This particular issue is with a Sea Apple <Uh-oh> it showed signs of not doing so well for a few days. There was a white portion of it looking like it was deteriorating and expelling its insides. <Not good> Since then and further observation the owner noticed that there was something inside the sea apple, it was a small crab or what looks like a crab. <Yep> Do you know or have heard of this happening, <Not specifically with Sea Apples/Pseudocolochirus spp., but I've heard of it in relation to other Cukes/Holothuroids. Sea cucumbers can be hosts to many different organisms, including Pearlfishes/Carapidae, Polynoid Polychaete worms, Periclimenes shrimps, as well as crabs (Pinnotherids, Portunids/Lissocarcinus orbicularis, Eumedonids/Hapalonotus reticulatus, etc.).> and what type of crab this is. <Looks to be a Pea Crab, family Pinnotheridae. These are small crabs that live in Cukes, tunicates, bivalves, etc., with varying degrees of commensalism to downright parasitism. While some live and do only low key, if any damage to its host, others can cause more threatening damage, such as atrophy of the respiratory organs/'trees'. Here are some examples of this family of crabs: http://www.unige.ch/sciences/biologie/biani/msg/teaching/photos%20liste/Pinnotheres%20pisum.JPG http://outdoors.webshots.com/photo/2762668420086890761xKfyFR > I attached a pic for reference, <Thanks, good photo!> up until the white deterioration of the portion of the apple it was healthy and doing well. Tank is a 150gal, 0 nitrates, salinity 1.024 and pH 8.4. <I'm guessing that the crab has been removed permanently from the Sea Apple. If not, I would do so. I would also recommend keeping a close eye on the Sea Apple for further decline. They can do significant damage to a system when they die! Please see this link for more information re: http://www.wetwebmedia.com/seacukes.htm > Joe Brillon <Take care, -Lynn>

Re: Sea Apple Hitchhiker: Pea Crab -- Now, Sea Apple in Trouble - 3/24/08 <Hi Joe> Thank you very much for your response as I have passed the info on. <You're very welcome.> It appears now that the area of concern has worsened. <I'm so sorry.> And the cause is unknown...any idea's what could of caused deterioration in the body of this animal? <No, I'm sorry to say that I don't. There are many possible causes including predation/picking/rough handling at some point. It could have gotten too close to a heater, pump intake etc, or it could be starving and deteriorating. These are notoriously difficult animals to keep. They need pristine/stable water conditions, a good supply of food, and lack of predation to survive - and in this case, to have a shot at recovery. Also, unless the Sea Apple is in a species tank/kept alone, I would move it to a quarantine tank to avoid the possibility of its poisoning the other tank's inhabitants. At the very least, I'd run carbon/PolyFilter, and have a large amount of prepared water on hand for a major water change should the Cuke decline further/die. Signs of decline would include deflation, expelling of insides, and losing color. Either way, I'd have a QT set up for either the Cuke to go into immediately, or the fish/shrimps, etc, to be moved into should the worst happen. Please see this link for more information regarding Sea Apples/tank poisonings. http://www.wetwebmedia.com/cukeselfaqs.htm > Joe Brillon <Sure hope everything works out for your friend and the Sea Apple. Take care, -Lynn>

Crab soup du jour?

LR Hitchhiking Crab ID Please: Xanthid and Possible Lissocarcinus sp. -- 3/20/08 Hi Crew, <Hi there Tracy!> I'm hoping you can help me id these two little guys that have been living in my Fiji live rock. They're crabs, but definitely not the ones I bought! Both very shy but have made a few appearances. They've doubled in size since we noticed them in our setup (now almost an inch across). They don't seem to bother any of our hermits or snails, however, 3 hermit crabs have gone missing, one of our newest has lost an arm, and our Skunk Cleaner Shrimp has just finished growing one of his arms back (we initially thought due to one very territorial yellowtail blue damsel). <Feisty little fellas!> Could these guys be the culprits instead? <If the two crabs are about an inch across the carapace (not including the legs), then yep, it's entirely possible. It could instead, though, be another larger hermit, crab, or even another shrimp depending on what species. There are lots of possibilities.> I've managed to narrow the first one down: <Good for you, I'm truly impressed! I know how time consuming and challenging this process can be!> ..it wouldn't be Hoplophrys oatesii b/c they're too spiny; it wouldn't be Mithrax cinctimanus b/c they're too fuzzy looking; could it be a variant of Lissocarcinus laevis or Lissocarcinus orbicularis??? The last seems most likely to me. <Yep, it could be that or something else in the same genus. Check the last/rear pair of walking legs for paddle-like structures on the tips. Lissocarcinus is in a family of swimming crabs, Portunidae, so the presence/absence of these should help confirm/exclude.> The second photo shows only the exoskeleton of the white-armed crab (his eyes are missing). I haven't been able to figure him out at all. <Looks like one of many possible Xanthid species (sorry I can't be more specific). Some are commensals, others just hang out in the rockwork/substrate. All are opportunistic scavengers (same goes for Lissocarcinus). As neat looking as both of these crabs are, they unfortunately have the potential to become destructive, particularly as they grow larger. You could try to deter predation by keeping them well fed, or instead place them in a sump or the like where they can't get into any trouble!> Thanks for your time and the great work you all do! Tracy <On behalf of Bob, the crew, and myself you're very welcome! Take care, -Lynn>

Crab ID: Family Menippidae - Predator! 3/18/08 Hi, <Hi there!> I was wondering if you could identify this hitchhiker for me. <I'll sure try!> At the moment he is about 1cm so very small. <Good> He only appears to come out when I feed the tank and is quite happy waiting for a piece of flake to drift into his home (I cannot of course be sure what he is doing overnight - probably terrorizing the tank!) <Yep, these guys are nocturnal predators. During the day, they seem to be mild mannered, snatching tidbits here and there, but at night it's another story! The shape and red eyes are very characteristic of crabs in the family Menippidae, Superfamily Xanthoidea, otherwise known as 'Reef' or 'Stone' crabs. I've seen similar (if not the same) crabs tentatively identified as belonging to the highly toxic if ingested(!) genus Eriphia (within the family Menippidae), but I can't confirm it. Although these claims could well be correct, a slight unseen/unrecognized physical characteristic could easily place the crab's classification elsewhere. Aside from taxonomic issues, these fairly common hitchhikers can unfortunately be very aggressive towards other crabs/invertebrates, as well as small fishes. At this size, it's not likely to do too much damage, but unless you've got a large fish, FO system, I'd think about moving it to a sump/elsewhere. Please see this link for an example of several crabs in the family Menippidae: http://www.geocities.com/ericdemuylder/menippid.htm. You can also see several photos of very similar crabs at WWM. Use the Google search engine with the terms 'Eriphia' and/or 'crab + red eyes': http://www.wetwebmedia.com/WWMAdminSubWebIndex/question_page.htm.> Many thanks in advance <You're very welcome! Take care, -Lynn>

Crab identity... no use of WWM, rudeness   03/15/2008 Help! I bought a small crab with light blue color on the top of the shell from my LFS. The store did not have another name for it and did not have any culture information. I am also wondering what I should feed the crab? Thanks Art <... Uhh... a terrestrial hermit? Saltwater, fresh? Try using the indices, search tool on WWM. B>

Re: Worm ID Please, Now Crab ID - 3/3/08 Hi! <Hi Cath, this is Lynn filling in for Bob this evening!> Thanks for the answer. <On his behalf, you're very welcome!> I've got now another ID for you. That was a little hairy crab who host a Monti colony of another reefer of my area. <Okay> Look at the joined pieces please and tell me if it is reef safe or not and if you can ID this crab. <Hmm, it's hard to figure out what's what in the photo, but it's likely a little (coral) commensal xanthid crab. As far as whether it's reef safe - likely so, as long as it stays small and doesn't irritate the coral too much. That is, if it's still alive. Judging from the use of past tense and referral to "pieces", I'm not so sure! If it is indeed still alive, I'd keep an eye on things, offer it small meaty bits (of marine origin) to deter predation and remove if necessary.> Thank you! Regards. Cath <You're very welcome! Take care, -Lynn>

Follow-up: RE: Worm ID Please, Now Crab ID - 3/3/08 <Hi Cath!> Thanks for the answer Lynn! <You're very welcome!> Sorry for my bad English, <Your English is just fine, so much so that I didn't realize it wasn't your first language!> I usually speak French and I have little difficulties with verb tenses!;-) <Well, I can sympathize as I have the same problems now and then myself and it *is* my first language!> Have a nice day!;-) <Merci bien et vous aussi! -Lynn>

Two Crabs and a White Nudibranch? 2/24/08 Hello crew! <Hi there!> I've attached a few pics of life (and former life) that I cannot identify. Whilst my intent was not malicious, the two crabs did not survive the extraction. <Unfortunate, but understandable - can be difficult to remove!> As you can see, one is missing several appendages. <Yep> I would've left them alone if my scarlet hermits were not being ripped to pieces at night <Yikes!> and if I hadn't read Calfo's opinion that crabs should be removed. <They can indeed be very destructive.> So, right or wrong, they are out and no longer alive. For the sake of learning and not repeating a mistake if they were harmless, can these be identified from the pictures I've provided? <They appear to be in the superfamily Xanthoidea. The hairy crab looks like it might be in the family Pilumnidae while the other could be in one of several different families. No matter, this group of crabs can be very destructive and I would have recommended their removal. Please see these links (and those within at WWM) for more information and photos for comparison: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm http://www.nhm.org/guana/bvi-invt/bvi-surv/crab-g06.htm> Also, there is a small interesting white (Nudibranch?) life form in my tank. Pictures also attached. Ideas about ID? <Unfortunately there are just too many possibilities. I can tell you, however, that due to their specialized diets, these little guys do not usually survive long term in most systems. Please see the following links, especially the section at the bottom of the first regarding issues associated with Nudibranchs: http://www.wetwebmedia.com/nudispt3.htm http://www.seaslugforum.net/ > Thanks so much. <You're very welcome! Take care, -Lynn>

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