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FAQs about Galatheoids called Porcelain/Anemone Crabs, Family Porcellanidae

Related Articles: Squat Lobsters, Hermit Crabs, Crabs

Related FAQs: Hermit Crabs 1, Micro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating Shrimp,

Bubble tip and anemone crab compatibility    2/28/16
I had a Sebae anemone which had an anemone crab associated with it which were separated due to some issues with chemical war fare going on in my 220. The Sebae is improving in separate quarters and the bubble tips that
remain are clones and one has been unhappy since the anemone crab took up residence. At first I thought maybe the continuance of chemical ware fare was the reason one of the bubble tips was not looking healthy but the sister to it is fine and inches away. It occurred to me that since that has been going on it is about how long the anemone crab has taken up residence so can they be an irritant to a bubble tip and cause this?
<Yes; can be>
It look better at night than daytime but it has been secluded in the shadows out of the light for about 2 weeks now. I run a lighted sump with lots of macro algae 24/7 and the only thing shut down at night are the tank lights and Tunze wave box. I run a canister filter with carbon. Was running 24/7 but my stony corals seemed to not be as active at night so I only run it in the day during feeding cycle.
Thanks in advance.
Mike Murphy
<I would leave all as is for a few more weeks; in the hope that the Entacmaea and crab will become accustomed to one another. Bob Fenner>
Re: Bubble tip and anemone crab compatibility    2/28/16

Never occurred to me that the problem I described with the Sebae Anemone may have been caused by the crab also as that was his residence  prior to the bubble which now is posing the same symptoms but almost immediately within days of hosting. I may not have chemical war fare after all
<Possibly. B>

New additions... Crusty Menagerie 3/19/11
I have a 120gal reef tank with multiple residents. I have 3 emerald crabs, a reef lobster and a fire and coral banded shrimp. Do you think I can add a porcelain crab or 2 to the tank. I just love the look they have.
<Umm, you may well have problems with the compatibility of the current crustaceans... reef lobsters are quite predaceous... the Stenopid only a smaller version/bit less... and the Mithraculus w/ growth/size, opportunistic omnivores like most all Decapods. Do see/read on WWM re all these... the Anomuran I would leave out unless you have a well-established symbiont for it/them to hide out in (stay out of the claws of the others).
Bob Fenner>

Anemone crab, incomp. 3/18/11
Hi everyone
Hoping you can help, about a month ago I bought two anemone crabs
<What/which species are these? Neopetrolisthes?>
and a mini maxi anemone,
<Stichodactyla tapetum I take it>
they both hung around the anemone until about a week ago, when one decided to live instead in one of my Rics.
<The anemone was likely "too sticky">
This was fine, until two days ago, when I came back for lunch, to find this crab had lost both large claws and one leg! which were at the front of the tank in the sand, then today found he had lost another leg! He is still eating with my help. What could have caused this?
<Mmm, a few possibilities... "the other crab" most likely, or other tankmate... But a reaction from the host/s, a dearth of biomineral, out of balance alkalinity, a host of mis-supplementing issues, lack of iodide-ate...>
my tank has been running for nearly a year now, and since the beginning have heard clicking (can be once or up to three times in a row) Mantis???
Stock wise - I have two hermit crabs, three sexy shrimps, two cleaner shrimps, one pom pom crab and the two anemone crabs, they have all molted regularly with no problems.
<Then not likely a system issue>
Fish -three Chromis, two clowns, one Banggai and one Tailspot blenny.
I know I have also go a nasty looking black crab with big claws and brown stripped legs,
<Oh! This could be the culprit>
have tried to get it out, but so far failed (tried glass, coke bottle and baited line) Could this have attacked the crab or could it be a mantis in the tank?
I have never seen a mantis in there and watch regularly at night with a red torch, nothing!
<I'd bait/trap out the unwanted decapods>
The other thing I have noticed are my Chromis which I have had since November last year, are now hiding at the back behind the rock, only come to the front for food, where they used to always be at the front swimming about, another indicator of a predator?
<I do agree with you>
I am thinking about stripping the tank down, but the clicking and the black crab are both in the very bottom rock, and I would need to take all out to get at it, and because of this I am very hesitate to do so, in case I cause a new cycle in the tank and loose all the inhabitants.
Please can you advise?
<Do read here: http://wetwebmedia.com/swcrabcompfaq3.htm
and the linked files above in this series... till you're aware of your possibilities>
Thank you for all your help
Wonderful site very helpful, keep up the good work!
Benita Pullen
<Thank you, will do. Bob Fenner>

Porcelain Crab And Sinularia? comp. 11/4/10
To the great folks at WWM,
<Hello Phil>
First time e-mailing a question. I have a 29g BioCube with 3g hang-on refugium a pair of Firefish, a pair of Yasha Gobies and Pistol Shrimp with some button polyps and a centerpiece of Sinularia sp. I was considering purchasing a pair of porcelain anemone crabs (Neopetrolisthes ohshimai) but was concerned with compatibility. I've read that they are peaceful crabs and that they can thrive even without a host anemone. My question is, do you think the crabs will be likely to attempt hosting in the Sinularia spp.
and if so are they likely to be detrimental to the coral?
<The Anemone Crab or Anemone Porcelain Crabs are most always associated with anemones in the wild and feed on meaty bits of seafood and mucus from the anemone.
They will live among live rock if no anemone is present, and are relatively hardy provided you ensure they are getting enough food.
It is unlikely that they would host the Sinularia, and if they did, they would likely irritate the coral.
If larger crabs are present in your system, the Porcelain Crab may fall prey to them. They are aggressive to other similarly sized crabs including the popular Blue Leg Hermit Crab.>
I love my simple little system and don't want to make any of my critters upset.
Thank you in advance!
<You're welcome. James (Salty Dog)>
Phil J.

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>

Another 'Crab ID': Must Be Porcelain Crab Season! 3/2/10
Hello WWM Crew!!!!
<Hello Sandra, Lynn here with you today!>
This little guy fell out of a piece of live rock I was moving out of my fish only tank.
I'm going to put him in my refugium as I know there are no truly reef safe crabs except for the commensal crabs in SPS corals.
<They're one of the safer groups anyway. They're generally small and stay within/around their particular coral, feeding on coral mucus, a bit of tissue and whatever else they can find.>
I have several of those and wouldn't dream of removing one.
<Good, I'd leave and enjoy them.>
He appears to be a filter feeder maybe in the Porcelain Crab family,
<You hit the nail on the head. It's a classic Porcellanid (family Porcellanidae) showing the distinctive 3 pairs of walking legs, two large claws and long antennae just behind the eyes. If you look closely, towards the back of the carapace on either side you'll see another small pair of legs folded up and held against the body. These are used for grooming. Up front, you can see the large mouth parts that open up into the distinctive fan-like structures used to filter organic particulate matter and plankton from the water column. All in all, it's a neat little crab.>
..but, of course, I couldn't find a picture that looks exactly like this guy.
<That's understandable. There are many, many, crab species out there. Knowing where the crab originated would help, but even then, it can be a considerable challenge. Sometimes you get lucky with a very common, well-known species, but most of the time narrowing the ID to family level is about as good as it gets.>
I have 2 in my 300 gallon SPS tank that don't appear to be bothering anything in their vicinity so I wanted to ask while I happened to have this one out what kind he is
<Unfortunately, a Porcellanid is about as far as I can take this ID without having the little crab in front of me to see all the pertinent/distinguishing details.>
..and could get a decent picture of him. If I need to get out the trap then I will.
<Well, if you want to keep that particular tank a fish-only, I'd move the crab to the 300g display. Porcellanids are generally small and don't have much negative impact on a reef system. They do scavenge as well as filter feed though, so I'd recommend offering it the occasional pellet food or meaty bits (of marine origin). Sometimes these crabs aren't able to obtain enough food from filter-feeding alone.>
The pictures don't show the color as well as I would have liked but he does have some red and blue accents.
<Yes, they show up fairly well after enlarging the photos. It's actually a very pretty little crab.>
I didn't know I even had this one until I took the rock out of the water and he fell out. The ones in my 300 I've only seen at night and they are actively moving their antennae and look like they are filter feeding.
<Typical behavior>
I haven't seen them picking anything off the rocks. I have 6 separate refugiums I could put him in. 3 with a DSB, rubble and Chaeto. 2 with larger and smaller pieces of rubble and Chaeto. And 1 with just rubble and Chaeto. Which refugium should I put him in to give him the best environment? I want him to have the right home.
<Hmmm, I'd either put him in the 300g display as mentioned above, or put him in one of the fuges with a DSB. You might want to add a couple of larger rubble pieces though so he'll have a place to hide. Crabs and other crustaceans like to hole-up in a secure spot when they molt as they're particularly vulnerable until their shell hardens. One other issue with the fuge relates to the Chaeto. Just make sure there's enough room at the bottom for the crab to crawl around. I've seen Chaeto take off to the point where it's packed top to bottom. For more information on Porcelain crabs, please see WWM, starting with the FAQ's at this link: http://www.wetwebmedia.com/SWCrabIDF15.htm >
Thank you all so much for the volumes of information and advice over the years.
<On behalf of Bob and the crew, you're very welcome.>
The changes you have made to the site to make information easier to find in the last year is awesome. Maybe 1 day you could add an image search feature similar to Google image search so you could scan through "hitchhiker crabs" images and click on the picture to go directly to the referenced page. That would be really, REALLY awesome.
<That's a great idea!>
Thank you,
<You're very welcome.>
<Take care, LynnZ>

Crab Identification: Porcellanid -- 2/23/10
Hello WWM crew,
<Hello Adam, Lynn here today.>
I have a question about a crab I recently found in my reef tank.
<Fire away>
I noticed someone else asking about what I think may be a similar crab on 1/24/10. That post noted Porcellanid but I have searched and not found anything that resembles this crab.
<Unfortunately, you may not be able to. There are many species, not all of which are available as photos on the web or within readily available books. Beyond that, there are species that haven't yet been formally described. For example, your little fellow could be locally known as 'Bob's crab' in some corner of the tropics, but until it's studied, described, and presented to the rest of the world, the chances of us running across any information/photos range somewhere between slim and none. It's frustrating, I know, but for our purposes, it's often enough to know which family the crab in question belongs within.>
Unfortunately I do not have a picture as it is the smallest crab I personally have ever seen. Perhaps 1/2 cm across.
<It could be a juvenile or simply one of the smaller species. Typically, these crabs are fairly small, with carapaces no larger than 1/2" across.>
It is a tan color but instead of claws it has 2 filter fans.
<Yep, you've got a Porcelain crab, aka a "false" crab ("Anomuran") in the family Porcellanidae. These crabs have 3 pairs of walking legs (as opposed to 4 in "true"/"Brachyuran" crabs), two claws (usually large, used mostly for territorial disputes but can be quickly shed when crab feels threatened), one significantly smaller pair of legs used for grooming that are held up against the abdomen or posterior end of carapace, two long antennae just behind the eyes, and two specially adapted fan-shaped mouthparts used to filter organic particles/plankton out of the water. As for the missing claws in your individual, they could have been dropped due to a perceived threat/stress, or lost due to injury/predation.>
They look just like feather dusters but are clear. It sits in the same spot all the time and I only see it at night with the flashlight. It just sits there and filters away with these fans. Opening and closing them in the current.
<Terrific observations! This behavior is typical of Porcellanids. Thankfully, they're filter feeders and scavengers that don't normally pose too much risk in a mixed reef system. I would offer it the occasional sinking pellet or meaty bit (of marine origin) such as shrimp, clam, silverside, or Mysis to supplement its diet. Unless you have a fully mature reef system, the crab may not be able to acquire sufficient food from the water column alone. For more information, please use our Google search engine and the terms Porcellanid or Porcelain crab: http://www.wetwebmedia.com/Googlesearch.htm >
Any insight would be greatly appreciated!
<Hopefully the above information/Google search results will help. If not, please don't hesitate to contact me/us. In the meantime, enjoy your little Porcelain crab!>
Adam Thompson
<Take care, LynnZ>

Sexy shrimp, porcelain crab, Perc clowns, and rbta compatibility? 2/11/10
I have a large BioCube
<An oxymoron... jumbo shrimp, military intelligence...>
currently with a RBTA and 2 juvenile (est. 6-8 months old) onyx Percs hosting in it, running on DIY LEDs.
The BioCube has SteveT's fishguard installed, and plastic mesh (sewing grid guide for yarn projects, as per Karen's Rose Anemones site) tied completely around the powerhead intakes, as part of my efforts to anemone- and fish-proof the tank.
I'd like to introduce sexy shrimps and/or porcelain crabs to this system.
I did some quick Googling and reading WWM FAQs and noted from some forum posts that porcelain crabs may attempt to boot my clowns out of the rbta, which is why I'm considering adding another (r)bta.
<Mmm, I wouldn't do this... unless they're genetic clones, there's too much chance of trouble twixt>
I'd probably get one from a fellow area reefer whose rbtas regularly clone themselves (in fact my current one is from him, it's healthy, feeding, and very colorful, etc.).
Is there any compatibility information on sexy shrimp, porcelain crabs, and clowns in a tank with a limited number of host anemone?
<I can/will only offer my personal observations here. Have seen Porcellanids and Clowns together in Carpet Anemone species in the wild... and Sexy Shrimp in Anemones that had or lacked Amphiprionines, but have not
"run" (or swam) into a situation where all three were resident in one such Actinarian species, and have never seen two of them in an Entacmaea. I don't know, but don't think this will work. Bob Fenner>

ID Crab: Porcellanid -- 1/27/10
Hi Crew,
<Hello there, Lynn here this evening.>
Is this a porcelain crab?
<It certainly is. It appears to be Petrolisthes galathinus, or at least one of the species within this complex. Common names include the Purple Porcelain crab and Banded Porcelain crab (family: Porcellanidae). They're primarily filter feeders, but will scavenge as well. Bob has also noted that they're not to be trusted around other invertebrates so beware if you have any. See this link re: http://www.wetwebmedia.com/galatheids.htm >
I don't keep crabs not even hermits because I have a small tank with small fish.
<That's understandable. Fortunately, these shy, mostly nocturnal crabs stay fairly small (carapace width to ~1/2"). Those big claws are mainly for territorial squabbles and are sometimes shed if/when the animal feels threatened. See this link for a photo of P. galathinus feeding. http://www.animal-image.com/CoralReef/Crabs/Banded%20Porcelain%20Crab/slides/BandedPorcelainCrab_PetrolisthesGalathinusTRCr_Ap8R.php >
Got this by mistake in an order. Keep it or not?
<It's up to you. While these crabs pose less threat than say, a big Xanthid, they're still scavengers. I just can't tell you for certain that it won't go after sleeping fishes if it gets hungry enough or the opportunity presents itself. One way to lessen those chances further is to keep the crab well fed with meaty bits (of marine origin), sinking pellets, etc. Honestly, I think it's a neat little crab. As long as I didn't have a tank full of tiny fishes (gobies and the like) I'd be tempted to give it a chance. Take care and good luck, LynnZ>

Mystery Crab: Likely Anomuran: Porcelain Crab -- 10/17/09
<Hello Jan, Lynn here this morning.>
I have a new Red Sea Max 1250 tank set up just with live rock for the moment and have 3 crabs? These have a large claw, small order pincer thing and banded legs but the body is tiny, much smaller than the big claw. They seem to feed by two feeler things which go up and down to the mouth in sequence and these have two large fans attached. Look a bit like a Spanish dancing girl!
<Heee! Very observant! What you describe is typical of Porcelain crabs (family Porcellanidae). Those 'fans' are used to filter organics/plankton from the water. For more information on these neat little 'false' crabs, please see the FAQ titled 'Mystery Crab (actually an Anomuran) -- Likely Porcelain Crab -- 8/16/09' at the following link: http://www.wetwebmedia.com/squatlobfaqs.htm >
Any idea what they are and if dangerous,
<Luckily, they're not dangerous to humans (beyond the possibility of getting pinched), but like most crabs, they're opportunistic critters so do keep them well fed as noted at above link.>
I have not yet put anything in the tank just cleaning crew snails and a blued legged hermit.
<Oh, you're just getting started! Enjoy the process and all the critters that show up, including these neat little guys!>
Many thanks.
<You're very welcome, it was my pleasure.>
Jan Randall
<Take care, Lynn Zurik>

Re: Mystery Crab: Likely Anomuran: Porcelain Crab -- 10/17/09
Hi Lynn
<Hi Jan!>
Many thanks for the fast reply.
<All due to your terrific description!>
I think the animal is an Anomuran although mine don't look like any picture so far, so is probably Anomuran randallis!
<Heeee! There are many genera and species in the family Porcellanidae so identification to species level can be a real challenge. If you can get together some good photos though, and tell me where the crabs/rock originated, I'd be glad to give it a try. I may not get it to species level but I might be able to narrow it to genus. Even that can be an accomplishment! If you do get a chance to take some photos, try to get a good one from above showing the carapace, all the legs, and the claw arms. Also, if you can get a good close-up of both claws/arms, that would be terrific. The more detail you can capture, the better chance we have of success! Oh, and one last thing, if you remove the crab to a bowl of tank water to take photos (keep crab submerged), don't be too surprised if the little fellow loses a claw or two. These guys sometimes drop them when feeling threatened/stressed, but with good health/husbandry, they should be back within a few molts.>
Great to know I can ask the experts when I get stuck.
<Heeee! I'm no expert, but I'm happy to help anyway!>
Best wishes, Jan.
<Same to you, Jan. Take care, LynnZ>

Re: Mystery Crab: Likely Anomuran: Porcelain Crab -- 10/18/09
<Hi Jan>
Right, will have a go when I can.
<Sounds great. I look forward to seeing the little fellows!>
Best wishes, Jan.
<Thanks, Jan. Take care, LynnZ>
Me too.

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 decapods (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>

Pls forgive me 6/30/09
Lynn... have placed yet another very generic "whatizit" invert. query in your in-folder...
Hi Bob!
Heheee! No worries, I'm working on it right now. One looks like a sea spider...the other crab(s) I can't quite tell. Right now I'm manipulating the photos every way I can think of trying to determine whether there are 3 walking legs on each side or four and whether there are antennae just distal to the eyes. It's not going too well so I'm about to call it a day - or at least a crab!
Take care,
<Mmmm, yumm, I wish we were having spicy crabs in Bali right now... Oh, the mess! Worse than any/all Olde Bay incidents! BobF>
<<Heeee - now that's something! Just eating blue crabs with all the Olde Bay seasonings, etc on them is a gigantic mess - I can't imagine trying to eat crab covered with a thick spicy sauce! What a mess indeed, but I bet it's well worth it! -Lynn>>
<Oh yesssss! Then you can eat the juice et al. as a sort of soup/compote at the end! BobF>

Re: Aiptasia? Now, ID's: Sea Spiders and Crabs -- 6/30/09
Hi Bob,
<Hi Peter, Lynn here today>
Thanks for the help ID'ing those.
<On behalf of Bob, you're very welcome!>
Since my peppermint shrimp isn't going for them, I may try some Joe's Juice or something of that sort.
<Aiptasia-X reportedly works well along with the standard Kalk/water method (Google for more info at WWM: http://www.wetwebmedia.com/Googlesearch.htm).>
Wondering if you could help me out with ID'ing these things and crabs from my new 46 gallon tank.
<I'll sure try.>
The tank is about three months old and I have some new hitchers I haven't seen before. There are some tiny spider-like animals. I have at least three of these. They are about 1/4 inch across. Not sure if they are small arrow crabs?
<I don't think so. I can't quite see the body, but overall they look more like Pycnogonids/sea spiders to me (carnivorous marine arthropods). Please see the following links for more information: http://www.wetwebmedia.com/pycnogonids.htm
http://en.wikipedia.org/wiki/Sea_spider >
There are also some larger crabs, at least three, all with the same coloration. The largest of these is an inch across.
<Gotcha. Unfortunately, I can't quite see enough detail to ID but with your help I think we can narrow down the field of possibilities. First of all, do the crabs have 3 walking legs on each side or four (not including claws)? Also, do you see any long antennae just behind the eyes (they may be fairly clear so look closely)? Those two factors alone can help us determine how safe these crabs will likely be around your fish. Generally speaking, if it looks like a crab but has three pairs of walking legs + long antennae positioned behind the eyes, it's a false/'porcelain' crab (Family Porcellanidae). These are primarily filter feeders but they also scavenge. The good news is that they don't pose nearly the risk to fishes that true crabs do. True crabs have four pairs of legs (most adapted for walking, some species' for swimming) and fairly short antennae placed in front of (between) the eyes. These are opportunistic creatures that will, if given the chance, make a nice meal of any fish, fellow crustaceans, etc. This risk increases with size, competition/lack of sufficient food, and ease of access (especially small bottom dwelling or sleeping fish, crustaceans in molt, other benthic invert's). For more information on porcelain crabs and true crabs, please see the following links (as well as associated links at the top of each page):
http://www.wetwebmedia.com/galatheids.htm >
I guess I was wondering if they will be hazardous to my 1-inch ring-eyed goby or yellow clown goby. There are the only fish in there so far.
<See above. If those crabs have 4 legs on either side, I'd get them out and find them a new home. Small Gobies and crabs are not a good combo!>
Thanks again for the previous early response!
<Again, on behalf of Bob, you're most welcome!>
<Take care, LynnZ>

Porcelain Crab vs. Mantis Shrimp. No Contest 11/23/06 Hi crew <Hi Kerryn> I've found your site very helpful with a lot of my questions on marine tanks, just a new comer to the marine world now having my tank running for a year, have made all the mistakes but I've learned by them as well, but one problem I can't solve is a with an anemone porcelain crab, I have searched the net for hours trying to find the answer. I have two anemone porcelain crabs that live very happy in an anemone each, one had a green algae forming on the top of its body, I thought this was a normal process maybe the crabs shell was getting old and was ready to shed, but obviously not, I woke up this morning to find him on his back in the middle of the tank, I did find some information about a disease that forms on a porcelain crab but didn't mention what it looked like? I do have a mantis shrimp cutting about in the tank, I can see a nip out of the crabs claw its black around the wound, I don't know how long the wound has been there, it's known that they will shed a claw or leg if threatened, everything is running brilliant in the tank, temp is 24 to 25 degrees, would really like to know what happened to it I've only had them two and half months-ish. <I'm surprised they lasted that long with that "Hit Man" you have in the tank with them. Mantis Shrimp belong by themselves and will kill, dismember, and eat crabs, shrimp, etc. along with smaller fish that it can sneak up on during the night. He is going to have to go or the other crab or a fish will be next.> Cheers <And to you, James (Salty Dog)> Kerryn.

Funny Trigger Story - 09/23/06 I just moved my three-inch male Blue Throat Trigger from quarantine to the display tank 24 hours ago, and he has remained hidden in a nook in the rockwork of my 90 gallon tank ever since. <<Not unusual...can be rather shy/timid as triggers go>> I'm not worried about him. He acted the same way in quarantine for the first three or four days only to come out and be friendly for the following month. <<Indeed>> I have two RBTA (a recent split), a B/W Ocellaris Clown pair, a Twin-spot Hogfish and a small Wheeler's shrimp goby that hasn't found his pistol shrimp yet. I have probably twenty snails, two large cleaner shrimp, one hermit crab and one small porcelain crab that came with some live rock, all running well and getting along for the past seven or eight months. <<Excellent>> Anyway, the trigger has taken up residence in the same cave as the porcelain crab. <<The porcelain crab hasn't taken up residence in one of the anemones?>> Now here is the odd thing. The crab, which can't even be an inch long, seems to be trying to bully the trigger out of its hiding spot. <<Amazing creatures we keep, eh!>> They seem to have come to an arrangement and aren't bothering each other at the moment. <<Ah, yes...and will likely cohabitate just fine>> I just thought y'all would like to hear about a tiny crab picking on a trigger that is probably twenty times his size. Thanks y'all for the wonderful work you do. My fish and I owe you for all of your great advice. Jonathan <<Were pleased to be of service...and thank you for sharing. EricR>>

Porcelain Crab Concerns 8/22/06 Hello All, <Hi there> You guys get a lot of question from folks that have real problems, and you provide excellent, thorough answers. My question will seem rather silly. But, I have a need to know. I have a white Porcelain crab with brown spots. I recently purchased a BTA in which my crab has taken up residency. Totally expected. What I didn't expect is for my pretty crab to turn all brown and yuck. Is this normal? Thanks, Jacqueline <Not unusual... may well change back over time. The adjustment of these Squat Lobsters to new hosts can result in such changes. Bob Fenner>

Peppermint shrimp and porcelain crabs... and Mantis and Clowns 7/18/06 Hi.. <Hello there> I have a 55 gallon display tank that is being left fallow while my fish reside in a QT tank. I am well aware of the dangers that mantis shrimps pose, and I know that one lived in my tank because I often saw him and he killed my coral banded shrimps. Now, I have not seen the mantis shrimp for over a month and I no longer hear the clicking noises they make. <... may be nothing to "click" about (live food items) present> As an extra precaution I added some feeder ghost shrimps into my tank and they show no signs of being attacked. <Oh! Good move> Is it safe now to add 2 peppermint shrimps? My tank has plenty of live rock and hiding places. <Only trying can/will tell> Also, I had an anemone crab that was kicked out of the anemone by my pair of very aggressive tomato clowns. He lost about 6 of his legs and disappeared. <Yikes, hopefully the legs will regenerate in a molt or three...> Now that my tank is devoid of fish, I was thinking of adding a pair of porcelain crabs. If I let them live in the anemone for 3 weeks before I put the pair of clowns back in, will they co exist within the same large anemone? <Again, only experience can tell...> Or should I get another anemone so they have one each? <If this system is "large enough" this might work... It is not altogether improbable that the Clowns will "hog" all anemones...> Thanks for your help. A <Welcome. Bob Fenner>

Buying from the internet and Neopetrolisthes maculata "Anemone Crab" Dear Wet Web Crew, <Zach> I have a 60 gallon reef tank is in dire need of snails and crabs, to pick up some detritus and unwanted algae. <Maybe> I have tried to find articles about buying from the internet. I would like to know what you guys think about buying crabs and snails from the internet... <Can work> ...and if you guys think it is safe then what are some reputable sites to buy from. <Best to query the BB's re... ReefCentral, WetWebFotos...> I have done some research and pricing and the internet is much cheaper than the local fish stores. <Depends on your definition of "cheap"... worth the sight-unseen risks? Hassles?> I also have a few quick questions about Neopetrolisthes maculata crabs. I interested in them and wonder how many are recommended for a sixty gallon tank, do they need an anemone or will they live happily under similar coral? Thank you for your time and help. <Do best in the presence of cnidarians... either anemone or soft corals... Are you ready for such? Bob Fenner>

Re: Establishing my live stock plan... Hi Mr. Fenner! Thanks for your help! <Welcome> I didn't see what you wrote about the flame scallop on WWM, but I did look at it after I received your reply. So I am definitively removing the flame scallop and the Dascyllus trimaculatus from my list. <Good> I appreciate these advices. It's interesting how some dealers make it sound much more simple http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=1525 I'm also giving up the Jawfish as it won't be completely satisfied anyway with a 4" DSB (and I don't want deeper for aesthetic reasons). Regarding the hermits, I will limit to three specimens (among these two smallest species: Dwarf Red Tip Hermit and Dwarf Blue Leg Hermit). <Okay> Now about the pair of Porcelain Crabs (Petrolisthes sp.), I didn't intend to keep an extra anemone for them. I am aware that keeping an anemone in a peaceful coral reef system is not without risks and planned to limit it to a single Entacmaea quadricolor (as per a previous advice you gave me :) to match with a clownfish. I thought this species of crab didn't need an anemone. At least that's what I understood from what I read on Foster and Smith http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=1963 <Mmm, a bunch to say... the genus Petrolisthes is generally not utilized in the trade, but often they are mis-labeled Neopetrolisthes (see here: http://www.wetwebmedia.com/galatheids.htm ). If you take a look on the Net re Petrolisthes... you will see this is a large, diverse genus of Porcellanids... My real point/intent is to encourage you to contact Drs.F&S and verify the species they are handling... > Couldn't find the species in Baensch. Also don't want them to fight with the clownfish for the anemone. Will continue investigations about all that (but if you have some hints...). <Please follow-up... look in B. V.1 under Neopetrolisthes> What are the risks involved with a generous use of "cleaner uppers"? My first guess would be that a heavy cleaning crew will ironically mean some more "pollution" because of the heavier bio-load, or is it something else? <Mainly that these animals aren't simply "cleaner uppers", but "eater uppers"... if there are too many of them, they will consume a good deal of things you might want to keep... including each other> Lastly, can you name a couple of your favorite smaller/est most useful non-sifting brittle stars (may want to add one or two of these)? <Oh, look through Baensch Marine Inverts V. 3... though it is difficult to actually order Ophiuroids by species in most cases. Bob Fenner>

Crabs dying Just a quick question for you. I have a problem with my hitchhiker crabs dying. I've found 3 dead crabs so far all of them flat bodied large flat clawed crabs, they do look like a porcelain or anemone crab which I believe are squat lobsters. Anyways my hermits and snails are fine but not the hitchhikers, any reason why? I also purchased an anemone crab a few days ago and haven't seen him since (or his body). I do have an anemone that came attached to some live rock as a bonus. Thanks a lot, sorry if I wasted your time, you don't have to answer if you feel it's trivial question. <Sharon, it is possible they may be members of the Porcelain species. In that light, all porcelains actively feed on particulate organic matter drifting in the water. If that is the case, the food requirement probably wasn't met. You are sure the dead crabs are not molt skeletons, correct? I've also posted a link here on the squat lobsters you may enjoy reading. http://www.wetwebmedia.com/squatlobfaqs.htm James (Salty Dog)>

Question on porcelain crab Hello Robert, regarding the crab I suggested you to be a porcelain crab (under Calappa sp. in your webpage), I wanted to ask you if you know where this crab comes from, since we found a similar one in the southern Caribbean. Does it come from the coasts of the United States? This information would be very useful for our research! Thank you in advance, Alexandra <Unfortunately, this specimen was "simply" on sale at a Los Angeles, California marine livestock wholesalers facility when/where I photographed it... labeled as a "Calappa sp. Crab". I am unaware of its origins. Could you provide a reference on the Net re this identification to family? Bob Fenner> Alexandra Hiller Institute for Animal Ecology and Systematic Zoology Justus-Liebig-University Heinrich-Buff-Ring 29 (Tierhaus) 35392 Giessen Germany
Porcellanidae key
Hi Bob, these is a site where you can find some identification patterns to the family Porcellanidae. I could not find one with a real key, but if you need one, I could send you one or send you some references (papers or books) where you could find one. We think the species you show in your web is a member of the Petrolisthes galathinus-species complex (Werding, 1982), that is, many species (about 5 or 6)that are very similar to the species Petrolisthes galathinus. We do not think this species (the one you show) occurs in the East Pacific (you mentioned in a former email that you photographed it in L.A?). Do you know where it could come from or maybe someone who could give us a hint? <Thank you much for this continuing input. No need for references, the key below will suffice. As stated previously, it is unfortunate that almost all wholesalers do not label the origin, other environmental information on tanks, shipping invoices... Perhaps in the future. Bob Fenner> Key to Porcellanidae http://www.nhm.org/guana/bvi-invt/bvi-surv/anom-inf.htm This is a program you can download from the internet (maybe you know it already) and it is very didactic. It only identifies an organism to the category suborder (this case Anomura), but it includes good information on all taxa this group includes. http://www.crustacea.net Best regards, Alexandra Alexandra Hiller Institute for Animal Ecology and Systematic Zoology Justus-Liebig-University Heinrich-Buff-Ring 29 (Tierhaus) 35392 Giessen Germany Tel: +49-641-9935648 Fax: +49-641-9935639 <Again, thank you for your input. Bob Fenner>

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