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FAQs about Marine Crab (Including some Anomurans) Identification 17

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 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 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,

Possible ID please? snail and crab 11/13/10
Greetings to you and the crew,
Once again I find myself relying on your expertise to sort out the miss-information I've gained through my research attempts.
The snail I have come to believe could be a whelk of some sort... but have also researched that since this shell does not display a body two times longer then the spire, so it isn't.
<Mmm, give a read here: http://reefkeeping.com/issues/2005-11/rs/index.php
Unfortunately, I can not confirm where the little guy is from. All the live rock is about a year or more old and was touted as a combo of Fiji and Florida, with any frag/coral spending 8 to 10 weeks in isolation minimum... so I actually have no idea how long it has been in there. I have him in a container with a small piece of krill mash hopeful to observe it eat as I have read that whelks can/do not eat algae - but apparently being captured has put off his appetite. Could you possibly confirm what he is please?
<Likely a Conch...
On a side note - could it be the reason for the die-off on the Monti?
<Mmm, not at all likely>
The crab was found on a piece of Haitian rock (still in isolation) and I am thinking Mithrax...
<The genus? Nah>
'cept I can't find any as fuzzy or grainy as he is. Of course, there isn't a wealth of 'identified' crab pics out there either:) Another description leans towards
a Black-Finger Crab, but they generally do not show/have fuzz. Presently he resides in a 3L Nano cube (no... not a typo) with chelto (spelling?) left in at all times, Nori, veg and meat flakes, and krill. I can't verify which he is eating. Again I ask... Can you ID please?
<Not from this pic, no. Bob Fenner>

little crab inside my rock 9/28/10
Dear Sirs,
I found this little look alike crab in one of my rocks (see the pic enclosed).
<Umm, this is a Stomatopod... A Mantis shrimp>
Could you please indicate my what is it exactly? and what does it feed on?
<Read here:
and the linked files above>
Thanks a lot
<Watch your hands. Bob Fenner>


Mystery Crab - Friend or Foe? 9/6/2010
Since transitioning to saltwater almost a year ago, I've spent countless hours reading articles and posts on WWM -- on dial-up, no less! I have found it to be a valuable resource in my saltwater tool chest.
<Ah good>
We have found/identified many critters that hitch-hiked on our Caribbean live rock -- some good (tunicates, corals, sponges, brittle stars, filter feeding cucumbers), some questionable (urchins), and some bad (mantis shrimp). However,
I haven't had much luck identifying this rather attractive little crab.
<Mmm, me neither... from the body shape, black tipped principal claws I'd state it's a Xanthid though...>
The shell is approximately ½' inch across, 'furry' legs (much like my Emerald crabs), 4 sets of walking legs, peach/orange in color -- with some darker spots, black tipped pinchers, nocturnal. No observations to report, since it only appears in pitch darkness -- and immediately hides when I try to spy on it with a flash light.
Attached pictures are of molt, not actual crab -- which I could not photograph.
Hopefully, it will be sufficient to assist with identification.
I have a mantis shrimp trap -- would this work for catching this crab, should that be deemed necessary?
<Should work, and I would remove it...>
Thanks in advance.
<Welcome. Bob Fenner>

Crab ID -- 8/21/10
<Hello Krystal, Lynn here today.>
Couldn't find a photo of this critter in the crab ID section. Any ideas?
<Heheeee - yes! Right now I'm wishing for the umpteenth time that either I was the leading expert on crabs and knew all six some-odd thousand species, including all the color variations, on sight, or that there were only a handful of species worldwide! If either were the case, you'd have your answer in a heartbeat. Unfortunately, we're not so lucky. At the moment, all I can really tell you with any certainty is that what you have is indeed a true crab (Brachyuran) and that it's a female. To take it any further, I'd need a bit more information. For instance, do you know what part of the world the crab came from? Did it hitchhike into your system on a particular coral frag and if so, what type of coral? Finally, what's the size of the crab? To be honest, most of the time, we're lucky to get crab ID's narrowed to the family level, much less to genus or specie. Just bear in mind that all crabs are opportunistic and none are strict vegetarians. They tend to be fairly innocuous when small, but can turn into real problems as their appetite, and body, grows.>
Krystal Wessels
<Take care, Lynn Z>
Re: Crab ID - Possible Liomera sp. - 8/21/10
Hi Krystal,
I did some research after replying to your initial email and may have gotten lucky. Your crab looks an awful lot like a Xanthid in the genus Liomera. Take a look at the photos within the following links:
Note the variations in color for Liomera tristis:
I can't guarantee that's it's the exact species, but it's close!
Take care,
Lynn Z

Follow-up Re: Crab ID - Possible Liomera sp. with a Taste for Corals! 8/24/10
<Hello Krystal, Lynn here again.>
The Liomera definitely eats coral.
I gave her the option overnight of Mysis shrimp or Pocillopora, and the Pocillopora is nearly half eaten with no missing Mysid shrimps. Just an FYI :-)
<Yowza, thank you so much for the update! The next time I come across this little crab in an ID query, I'll be sure to let the person know that it has a taste for coral!>
Krystal Wessels
<Take care, Lynn Z>

Hitchhiker (Xeniid) crab ID 8/11/10
Hello there!
I found this tiny hitchhiker crawling out from one of the stem of my newly acquired Xenia colony!
It seems to be called Xenia crab but I could not find any further information about it other than a few pictures from the web (and on your wonderful site).
I was hoping you could help ID this crab for me?
Many thanks!
<Have seen this in the wild... believe it's a Lissocarcinus species...
search this with the term Xenia commensal. Am putting in LynnZ's in-folder as well. Bob Fenner>

Hitchhiker Crab ID: Porcellanid Xenia Crab -- 8/11/10
Hello there!
<Hello Jason, Lynn here this afternoon!>
I found this tiny hitchhiker crawling out from one of the stem of my newly acquired Xenia colony!
<It's a pretty little thing isn't it!>
It seems to be called Xenia crab
<Yep. There are photos of them all over the web, in various BB's, and within WWM.>
..but I could not find any further information about it other than a few pictures from the web (and on your wonderful site). I was hoping you could help ID this crab for me?
<Hmmm, well I can tell you that it's not a true crab (Brachyuran), but instead a false crab (Anomuran -- hermits, mole crabs, squat lobsters, etc.). More specifically, it's a Porcellanid (Porcelain crab) of some sort. If you take a good close look at the photos, you can see that the last (almost transparent -- very hard to discern) pair of legs is folded up and held against the body. Of note is that although these legs are mobile, they're not used for routine locomotion. Instead, they're apparently used mainly for grooming. True crabs, by comparison, use that last pair of legs for walking, burrowing, or in some cases, swimming. Now, as to species, unfortunately, I can't tell you with any certainty exactly what you have. I can tell you that I found a photo of what appears to be a color variant of the same crab in Poppe Images, and they ID it as Porcellanella triloba: http://www.poppe-images.com/?t=17&photoid=909792 . It has the same dome-like carapace and serrations on the outer edge, the same gracile, slightly curved claws, same claw arm proportions, and the same general color pattern. What's important to note is that the two also share a rather flattened/straight area between the eyes. There are no apparent projections of the carapace. The problem I have with this ID is that every other individual that I've seen with the same species name, has a distinct series of 3 projections between the eyes. You can see them at this link (note species name): http://www.poppe-images.com/?t=17&photoid=942351
That's completely different than what we see in the first photo. Am I saying they got the ID wrong? It occurred to me, yes, but for all I know, the crab in the first photo could be a juvenile; who knows? I'm not exactly the authority on crabs. Given the choice, I'd go with their judgment over mine. Now, as far as more information on these guys, I can tell you that they're mostly nocturnal and are usually found in pairs so bear that in mind if you decide on removal. As far as whether to keep it/them, it's up to you. The general consensus seems to be that they're better kept within a large Xenia colony than a small one, mainly because any potential predation has less overall impact and is less noticeable. Unfortunately, I can't tell you one way or the other whether your crab will devastate your colony or simply take a nip here and there but otherwise be fairly innocuous. If it were me, I'd leave the little crab as is, but keep a sharp eye on the Xenia. At the first sign of trouble, I'd remove the crab and place it elsewhere. Please see the following link for more photos of the crab similar to yours (also see Porcellanella picta) and other examples of Porcellanids on subsequent pages: http://www.poppe-images.com/?t=11&family=porcellanidae&p=1 >
Many thanks!
<You're welcome!
<Take care, Lynn Z>

Help Identify: Two Florida Crabs -- 4/4/10
Dear Wet Web Media
<Hello Dominick, Lynn here this evening.>
Hello once again I would like to express what a wonderful website you have.
<Thank you!>
I am attaching two pictures of two different crabs, can you please inform what species..
<Unfortunately no, I can't. There are an awful lot of crab species out there and I can't see enough pertinent details in either photo to be able to offer a species ID. When it comes to identifying crabs, it's all in the details. These include shape/texture/color of the overall carapace, whether it's smooth or 'hairy', the number of spines/shape of the carapace edge, eye placement/color, length of eye-stalks, how many legs, the shape/length/color of legs and claws and whether there are any 'teeth', spines, bumps, etc, on them, the shape of the tips of the claws (are they pointed, blunt, or spatulate), the depth of the body, etc, etc, and that's just the basics. The list of criteria goes on and on! The best way to ID these guys is to have them directly in front of you so that you can pick out all the little details. Most of the time, we're doing well to narrow things to the family level. I'd recommend looking through Bob's crab article (see link below), as well as any online sources offering photos of crabs from Florida. You might want to perform a search using the genus Mithraculus or Mithrax in Google's Image search engine for help identifying the olive green crab: http://images.google.com/imghp?hl=en&rlz=1T4GGIH_enUS263US264&tab=wi
Regarding the white crab, does it have dark claw tips? If so, it could be some sort of Xanthid (family Xanthidae). Here's some very basic info on the family: http://en.wikipedia.org/wiki/Xanthidae
Here's page one of Bob's article: http://www.wetwebmedia.com/marine/inverts/arthropoda/crabs/swcrabs.htm >
... and if they are reef safe
<It depends on what you consider reef-safe. Crabs are opportunistic omnivores that if hungry enough will eat anything they can get their claws on, including snails, other crustaceans, sleeping fishes, etc. There are no vegan crabs. I personally don't trust them, keep them, or recommend them but if you do want to keep these, I'd recommend offering them the occasional meaty bits of marine origin.>
I live in Tampa and my son and I went snorkeling and found these two crabs and put them in our reef tank.
<That's generally not a good idea. It may or may not be legal, but even if it is, you risk introducing disease, unwanted parasites, etc., into your system.>
I have never seen the white crab species before.
<I've only seen one all white crab from Florida: Dissodactylus primitivus, a tiny 'pea' crab that lives on Meoma ventricosa, aka the Red Heart Urchin. Here's a photo: http://www.cryptosula.nl/photos/Dissodactylusprimitivusweb.jpg
Your crab appears to be mostly white but possibly has some sort of pattern on the shell/carapace? If so, that could help you in your efforts to find an ID.
Thank you.
<You're very welcome.>
Dominick Perrone Jr.
Culinary Arts Teacher
East Bay High School
"Condiments are like old friends - highly thought of, but often taken for granted." Marilyn Kaytor
<Take care, LynnZ>

Acro Crab? Possible Trapeziid or Juvenile of Undetermined Family -- 3/28/10
<Hi Mike, Lynn here today.>
Just found this little crab on a new shipment I just received.
<Neat! What kind of shipment -- coral (Acropora, Pocillopora, Stylophora, etc.?), rock, or something else? Where was the shipment from? What's the size of the crab (carapace width)?>
Hoping you can confirm whether of not it's an Acro crab?
<That's a tall order! Did it hitchhike in on an Acropora colony? It could be a coral crab, or it could simply be a juvenile of some other variety. It has the same large eyes, roughly triangular carapace, and claw length/shape that you see in many Trapeziid crabs (family Trapeziidae -- aka 'coral crabs' or 'coral guard crabs'), but the color/pattern of the carapace is atypical. That is, it doesn't fit with what photos I've seen of Trapeziid crabs. The problem is that there are an awful lot of crab species out there, not all of which are available as photos on the web or in my research books. What you have may be a coral crab that in its juvenile phase has a completely different, more cryptic coloration, than its adult counterpart. This is not at all unusual in crabs, or other animals for that matter. Unfortunately, I haven't been able to find any photos of juvenile Trapeziid crabs for comparison. Again, there's the distinct possibility that this little crab could simply be a juvenile from any number of other families. Juvenile crabs typically have the same large eyes that you see in Trapeziids. The bottom line here is that unfortunately, all I can offer are a whole lot of maybes and no concrete answers. Time and behavior will tell with this little fellow. I can tell you one thing though. Trapeziids are generally found in the Pacific, either the Indo-West or tropical Eastern regions. If this little crab came in on a shipment from say Florida or the Caribbean, chances are it's not a Trapeziid. Please see the following link for an example of a juvenile Callinectes sapidus, aka 'blue crab' (see last photo). This is definitely not what you have (and not a variety of coral crab), but you can see the similarities: http://www.serc.si.edu/education/resources/bluecrab/lifecycle.aspx
Here are some examples of coral crabs, along with more info (see bottom of page): http://www.chucksaddiction.com/hitchcrabs.html
More info at WWM: http://www.wetwebmedia.com/Arthropoda/CrustaceanPIX/SWCrabs/Crab%20IDs/SWCrabs3.htm >
And good/bad?
<Time will tell. This could be a relatively harmless coral crab, or something else entirely. Since I can't confirm either way, I'll offer the standard crab warning. That is, crabs are omnivorous opportunists and scavengers that, if hungry enough, can and will eat pretty much anything they can grab with their claws. You have the choice of keeping, observing, and removing if/when the crab becomes a problem or playing it safe and putting it elsewhere until you have a better idea what it is and how much risk it poses to other livestock. Either way, do be sure to keep it well-fed with meaty scraps of marine origin (shrimp, clam, squid, fish, etc.) or perhaps sinking pellets.>
Attached a pic for ID.
<Thanks, he/she certainly appears to be an itty-bitty thing!>
<You're welcome!>
<Take care, LynnZ>
Re: Acro Crab? Possible Trapeziid or Juvenile of Undetermined Family -- 3/28/10
<Hi Mike>
Thank you for the response.
<You're very welcome.>
He was attached to a "purple monster Acro" from either the Solomon Islands or Fiji, my supplier only specified vaguely where all our corals came from, one or the other.
<Thanks, that helps. I just wish that it was enough to be able to offer you a positive ID! As it stands right now, I'm not sure what type of crab this is. As was evident in the photo of the blue crab (see link in previous response), appearance can change significantly from juvenile to adult. We should know more as this little fellow matures. Honestly, it could be one of many different genera (not just in the family Trapeziidae) that are associated with Acroporids. It could also be an accidental hitchhiker; that is, not a coral crab at all. Perhaps it was ousted from its normal habitat during collection and simply took refuge within the coral's branches.>
I've attached a not so macro pic for a naked eye view as well. He is tiny, maybe 3-4 mm.
<Yep, that is one small crab!>
Thanks again!
<It was a pleasure! I'm just sorry that I couldn't give you a more definitive answer.>
<Take care, LynnZ>

Crab ID, Please: Likely Decorator Crab -- 3/6/10
Good evening,
<Good evening Laura, Lynn here tonight.>
Thanks once again for providing such a wonderful resource.
<It's always a pleasure.>
I looked through your crab ID photos, but I didn't see anyone who looks like the critter that I saw tonight for the first time. We haven't purchased any live rock (or anything else) for months, so I was very surprised to see someone new.
<It happens, especially with little crabs like this one.>
The picture is a bit blurry, but if you have any ideas about who this is, I would love to hear them.
<Judging by the amount of 'stuff' it appears to be carrying around on its body, it's most likely some sort of decorator crab, family Majidae. These crabs collect bits and pieces of algae, detritus, sponges, hydroids, corals, etc., and attach them to their carapace and legs in order to blend in with the environment and avoid predation.>
Please let us know if he looks untrustworthy.
<All crabs look untrustworthy to me! They're opportunistic omnivores that scavenge and eat pretty much anything they can grab and hang on to. This little fellow appears to be fairly small so his diet most likely consists of bits of algae, detritus, and small invertebrates such as worms, feather dusters, etc., that it picks from the rocks thanks to a pair of slender claws. When/if this individual grows larger, it may add snails, hermits and other crustaceans to the menu. Unfortunately, there's no way I can positively ID the crab to species level, or specify its maximum potential size. If you do decide to leave the crab in place, be sure to offer it the occasional meal of pellet food or meaty bits (of marine origin) such as shrimp, fish, clam, etc., to help deter unwanted predation. For more information, please see the following links:
http://www.wetwebmedia.com/Arthropoda/CrustaceanPIX/SWCrabs/Crab%20IDs/SWCrabs2.htm >
Thanks again!
<You're very welcome!>
<Take care, LynnZ>

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