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FAQs about Marine Crab Identification 4

Related Articles: Crabs, Hermit Crabs

Related FAQs: SW Crab Identification 1, SW Crab ID 2, SW Crab ID 3, SW Crab ID 5, SW Crab ID 6, SW Crab ID 7, SW Crab ID 8, SW 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 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,

Jet Black Hitchhiker Crab   10/1/06 Hi Bob, <Sheldon> I had seen this guy a couple of months ago and have not seen him again until this evening.  I would guess that he has more than doubled in size in that time. <Yikes...> It was very difficult to get a picture of him because he was at the very back of my aquarium.  I grabbed the rock he was on in hopes of retrieving him, but, he jumped.  The crab looked like a Mithrax except that he was completely jet black.  Also, I have not purchased any Mithrax as I am not a fan of crabs in reefs. <Me neither> His legs did appear to have the little hairs you would see on a Mithrax and many others.  I will assume he is a member of the Xanthid family and attempt to set a trap, but, I wanted to see if you had any ideas as to what it is.  I will send a better picture if I catch him.   Take Care, Sheldon Wiseman <Can't tell from the pic, description, but I'd be removing this animal. Bob Fenner>

Crab ID, Care  9/23/06 HI, i looked on the site to see if this was addressed and did not see it.  We caught some snails and hermits and a small crab at the beach. I have a 55 gal. w/ several inhab.s The crab I believe is a blue crab...he is growing and has molted once.  So far he is eating  bottom material and he has bothered some of the hermits but has not eaten them. I have an emerald green, and red leg and several varieties as well as fish and mushrooms.  question...is he going to get huge and eat everything?? Should I remove him and if so who would want him? <<Not knowing where you caught them, and the average temp of the water there (compared to the temp of your tank), it's hard to give you advice.  Since it is usually not legal to collect critters at the beach, if you are having second thoughts, the best thing would be to drive by the beach and put them back. If you took them out of the ocean, it's your responsibility to take care of them and/or bring them back.  If you ever decide to do it again, you should research what they are first to see if they are compatible with the rest of your critters.  The books within this set are helpful for the creatures you may find in the warmer waters of the US.   http://www.amazon.com/Reef-Set-Creature-Coral-Volumes/dp/1878348337/sr=8-1/qid=1159037030/ref=pd_bbs_1/102-6884237-3938568?ie=UTF8&s=books  Best of luck, Roy>>

Unidentified crab - 10/24/05 Dear WetWebMedia Crew: <Art> I recently picked up a pre-established 40 gallon system which included numerous different species of corals, live rock, hermits, Nassarius snails, three fish (coral beauty, Gold Stripe Maroon Clown, and a yellow-tail damsel), <... the Angel, Clown may be trouble, crowded here in the long/er run, if any other fish is added> and an unidentified crab. I first noticed the crab when I was breaking down the system at the persons home who sold me his tank.  <I see... nice pix> Unfortunately, the person whom I bought the system from was less than knowledgeable about the contents of his tank almost to the point of being somewhat humorous.  (I was informed that the fish included in the sale were a "Koran angel", yellow tail, and a clown fish... only to discover that there was no Koran, only a coral beauty.)  Given his lack of knowledge, I realized that he did not know what was in the tank and that it would be useless to bother him with questions. From what he said the tank had been operational for over a year with no new additions and the animals thriving...as such, I made a mental note of the crab and figured I would determine the threat it posed later. The first few times I saw the crab it was always near some zoo's but did not appear to be picking at them. However, an hour later I checked back on the tank and found that he was in fact attacking the zoos and immediately removed him from my system. <Good> The question is, what species of crab is it? <Looks to be a Portunid family member... can't tell species> Should I feed him to a Zebra Moray or other crustacean eater or just toss him in a FO tank. I'm inclined to make the Moray happy. Thanks. Art <The choice is up to you. I would not keep this crab with your other current/listed livestock. Bob Fenner> 

Candy Cane and Small White Crab 10/22/05 Hi, <<Hello Ed, Ted here>> I have a candy cane coral in which there are three polyps that have a small crab living within the polyp. The crab is white and about 1/8 of an inch long. The polyp still seems healthy but there is an indent where the polyp has reshaped and the crab is sitting in. I called the LFS but they have never heard of it. Do you know if these crabs will eventually kill the polyp or if they have some type of symbiotic relationship? <<From the description, your candy cane may have Gall Crabs. I have found conflicting information on them with some recommending removal if you can do so without hurting the coral and others suggesting that if the polyps seem normal and feed to leave it be. In my opinion, if you can remove the crab without harming the coral, do so otherwise observe and hope for the best.>> Thanks, Ed <<You're welcome and good luck - Ted>>   

Crab Thievery - 10/19/2005 Could you help me ID this crab please? <I'll give it a go.>  It's about the size of a dime, maybe slightly larger.  He is smooth (not hairy at all).  At first I thought it was just holding on to the Zoa while eating it, but as it scooted off, he carried the Zoa with him.<Guess he liked it.> I would assume he is a bad crab, since he's ripping Zo's off the rock.<A nuisance indeed.> I wasn't able to catch him, but will continue to watch for it and try to remove it to the refugium. <Well Lies, I cant make out enough of the actual structure of the crab for a specific ID, but the behavior strikes me as some sort of decorator crab.  Look to see if he shows up with a new hat!  Will likely pick at and remove polyps as it pleases, and eat what ever is convenient.  If this does turn out to be a decorator you may be able to trade out to your LFS rather than place in you refugium. - Josh> Lies

Re: Crab ID Please  10/20/05 Dr. Ron identified the crab as a Gaudy Clown Crab.<He is much more capable at ID than I.> He didn't have any diet information for the species in his database, but said that since it is a xanthid,<Ahh, yes...the coral crabs.> it is suspect and could very well eat Zoas.<Yes.> OF course, I did see him carry a Zoa away with him! I was able to catch him and I did put him in the fuge; however, I'm not sure how long he'll live down there, not knowing what he eats. <Xanthids are commensal crabs (usually in association with Acroporids).  Omnivorous most likely.  Will likely not live long thrown into a 'fuge.  Truly meant to live in company of a coral host.> Besides, we keep our lights on in the fuge 24 hours a day, so he may never really venture out again. He really is a pretty crab.<Yes, and thank you for the beautiful picture.  I would suggest trying to trade him to the LFS rather than gamble with his "ability to survive in a 'fuge".  He does most likely desire "other" surroundings.> Here is a link to a much better picture of the species. My crab looked identical to this one. <Sorry but no link came through.> Thank you for your help! <Thank you for your question/proper ID follow-up.> Liesl <Josh>

Re: Crab ID Please - 10/19/2005 Sorry about leaving out the link. <No problem> http://www.dive-st-vincent-scuba-diving.com/PhotoGallery/Underwater_Photo_To ur_2002_Pictures/image016.htm I just thought you might enjoy the picture - it really is a beautiful crab.<Many Xanthids are.> He should be easy enough to catch, now that he's in the fuge, and take him to the LFS.<Never under estimate the resourcefulness of a crab.> I really hate to know I'm "killing" something - even if it does feed on corals.<Doesn't make it a bad guy, merely marine by nature. - Josh> Liesl

Tarantula Crab 10/16/05 Good day to you! <Yawnnnnn!> We have found a strange looking crab that resembles a Tarantula... he is brown with black spots and white hair all over his body. The insides of his claws are pearly white. I have attached a pic... he seems to be getting bigger FAST and am worried that it will soon be a nuisance or even a killer? <<Marina cannot find the message with the photo, but it was a very good shot.>><Sorry re Mar... must've deleted rather than moved... but did copy, will paste here... old habits... RMF> <Maybe... looks like a xanthid to me...> He must have been a hitch hiker that we did not see for a year or so until he got big enough to be confident enough to come out of the rocks... Just hoping you could assure me that his size (2-3 inch diameter). I also think maybe he has a small friend of a similar species living in another rock... only have seen the claws. Thank you, have a great day! Cora Fross in IL <Please peruse here: http://www.wetwebmedia.com/swcrabidfaqs.htm and the other Crab ID FAQs files linked above, and the cautionary remarks therein. Bob Fenner>

Crab id  10/5/05 Hello Bob. I have a reef aquarium and have recently spotted a small furry crab in it which seems to stay in the same spot at night when it comes out, it is approx 2 inches long, tan coloured and very furry, any help would be grateful. Jack. <Help? See WWM files on Crab Id's, Compatibility... Bob Fenner>

Acropora animal question  9/20/05 <Hi, Adam J responding to you this evening> I recently bought an Acropora sp. at one of my LFS.  I placed in my tank and found a small brown looking "bear" on the coral. <Even though your attached picture was a bit blurry you did a wonderful job at capturing the animal. It appears to be a common Acropora Crab, though identifying the exact species is much more difficult, but more than likely it is harmless.>   Is this safe to leave on the coral or should I try to remove it? <I would not remove it yet, though I would closely monitor it.  Most Acropora crabs are commensal, feeding off of the waist of the host coral. Furthermore they usually don't get very big. (Dime sized is the biggest I have observed) However a few have been known to pick off/feed on the polyps, so I would still keep an eye on him. 'If you are in doubt take him out.' By that I mean, if his behavior becomes suspicious (i.e. visible damage to polyps) I would remove the crab at earliest convenience.>   I'm including a picture of the animal; not the best quality picture. <The picture was fine, glad to have helped, Adam J>

Crab ID 9/19/05 To make a long story short, I work in the aquatics dept at a pet store. To make a short story even shorter, some girl brought a crab in to me tonight to give away, but I quickly learned that this girl (and me) know nothing about the crab, even remotely an idea of what species it is, since it was "rescued" from a sushi restaurant about a week ago.  <Mmmmm...  Crab hand rolls!  Most crabs are far better suited for food (human or fish/invert) than aquarium specimens unless you have a secure place to keep them.> I now have this crab set up in a small tank right here next to my computer until it either offs itself from my ignorance about it or until I can decide what it is and how to keep this nifty little guy alive. I was hoping you could help me with this. I'm sorry, I won't be able to supply a picture, but I'll try and make my description as complete as I can.  <An ID without a picture will be nearly impossible, especially since you don't have any idea where it came from.  It might not even be tropical.> The crab is rather small. It's maybe 2- 2.25 inches in circumference with the legs not outstretched, the main carapace alone is around 1 inch or so.  It's legs are rather long, about as long per leg as the carapace is wide, thin, and of a very bright reddish orange color from the tips clear up to the joints on the ventral side of the carapace. The ventral side is a solid white color for the most part, with only very faint traces of the reddish orange color around joints. The dorsal surface of the carapace is very dark, almost black at the anterior end around the eyestalks and abruptly fading to the same reddish color at the posterior end (about the last 1/8 inch posterior margin of the carapace) the color of which continues on to the legs as described. The two claws are quite large and prominent, with the right claw of the crab being noticeably (but not overtly, as with most fiddlers) larger than the left. Both are the same white color as the ventral side of the carapace and are quite striking. <This doesn't ring any bells.  I searched the internet, and there is no crab version of www.fishbase.org.  Unfortunately, size and the claw mismatch aren't diagnostic.  There is no way to know if the animal is full grow and if the claw size is due to previous injury.>   I tossed the bit about it being rescued from the sushi restaurant in there if that would maybe help at all. The crab has, apparently for the past week, lived in a small bowl of tap water and been fed bologna. I have upgraded his accommodations and food drastically, but have kept him in 100% fresh for the time being. He has been doing fine by all appearances for now, but I know as well as anyone should that could change literally within an hour... If you have any ideas, let me know as soon as you can! Thanks! <Hmmm... I didn't even think about the fact that this animal might not even be marine!  My only suggestion is that since it has survived this long in FW, to keep it there.  Feed it just about any kind of fish foods since crabs are omnivores.  There isn't much else you can do but feed it to some hungry puffers!  Best Regards.  AdamC.>

Crab ID Part 2 9/26/05 Thanks for the reply about the crab, and thanks for trying your best to help. I apologize for not being able to supply a picture, I know it probably would have helped drastically. But I be a poor college kid and money and neat useful toys like digi cams elude me... <Best save that money for fish stuff, pizza and beer! (if you are 21yrs, of course!)> I have settled on the fact that it must be some form of fiddler or another, and my roommate, with a few years of marine experience under his belt, seems to agree. He's largely active on land for most of the night and retreats to a little burrow he dug out of his substrate near the waterline during the day. Prodding him causes him to flare both claws, but wave his largest and snap it in warning.  <It is sounding more and more like a fiddler.  They can be maintained... do research their needs.  They are generally brackish and require an intertidal habitat as you have described.> I had heard from another source that marine crabs are able to live in FW for up to a month, but will slowly decline over that time. Deciding to try an experiment, I made his water slightly brackish, and discovered that he is suddenly spending more time underwater than previously. I am unsure however if this is a positive reaction or not. Any thoughts?  <SOME marine crabs can survive FW, however most will be harmed.  Those that can tolerate FW are intertidal, brackish or estuary species like fiddlers.> He appears to have been feeding, not filtering sand, but laboriously picking up little bits of food (crushed sun dried shrimp for now) one by one...As for feeding him to puffers, I'm sure Dot (my roomie's Leopard) would be more than happy to oblige, but this darn little thing has grown on me... Once again, thanks for the reply, it came rather sooner than I expected=) JB <Sorry for the slow reply this time.  Was away at MACNA and then awash in personal obligations.  In any case, this little fella will be a great pet!  Enjoy!  AdamC.>

Another Crab ID 9/19/05 I found last night what appears to be a mix between an arrow crab and a decorator crab.  He is about 2 1/2 " wide. Was tightly hanging onto my anthelia (and has been there for a few days without moving) It has what appears to be a total of 8 legs.  <Such large crabs are almost always at least minor pests if not down right destructive.> He sits upright on the four lower legs. Literally sits down on them as if that is there only purpose. The other four legs are fanned out in the water. These have like a Velcro texture to them. He attaches loose particles to them to completely conceal himself. (I though it was just algae hanging on. I had a little out break of Cyano algae and he covered himself completely with it.  His body looks very similar to an arrow crab with it being almost transparent. Doesn't seem to move at all.  Thanks for looking. Please let me know if you have any idea what this might be! Rebecca  <It is impossible to guess beyond saying that it is some kind of decorator crab.  An exact ID is really not necessary.  For the safety of your

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