Malevolent Crab? 4/2/13
Dear crew
<Hello, Lynn here today.>
I have a few of these crabs in my reef tank and don’t know if they are the kind I should have in there or not. 
<The short answer is no, since, at least the one photographed, is a “true” crab (brachyuran: two claws + 4 pairs of walking legs) as opposed to a porcelain/”false” crab (Anomuran, family Porcellanidae:  2 claws + 3 pairs of walking legs).  Brachyurans can have leanings towards various foods but they’re opportunistic omnivores that will eat just about anything when hungry and/or given half a chance. 
The longer answer involves examining the claws in order to get a better idea of a crab’s main diet.  Judging from what I see in the photo, your crab most likely has spoon/spatulate-shaped claw tips.  It’s believed that these are useful for scraping algae, etc., off hard surfaces, grasping filamentous algae, and/or scooping up soft materials (e.g. detritus and/or coral mucus).  It would be nice if these claw tips were indicative of a single family or genus, but they are found in many.  These crabs tend to be a bit better risk in reef tanks than say, a large, heavy-clawed Xanthid, or a more slender, sharp-clawed Portunid (swimming crab), but by no means does this make them “safe”.  They're still opportunistic omnivores that may be fairly well-behaved when small and well fed, but can be a problem later on as their bodies and appetites grow, and competition for food increases.>
I did not purchase them.  I guess they would be around 6 years old. 
<I can’t tell how large the one is in the photo, but even if the crabs you have are a smaller species, they are still capable of damaging livestock.>
They only come out at night.  I've lost a few small fish and can't seem to keep any shrimp around.  I figured maybe these crabs are the reason why. 
<That could be part of it, especially if the crabs are able to grab a shrimp when it's vulnerable during a molt.>
Any thoughts?
<Yes, if possible, I would trap/capture the crabs and find them a new home in a sump or elsewhere. Please see WWM regarding crab removal (3 pages, starting here: http://www.wetwebmedia.com/swcrabcomp.htm >  
Thank You
<You’re most welcome.>
L. Splitter
<Take care, Lynn Z>

What is this crab – 02/20/13   
We found this crab washed up on the beach on Ft Myers Beach Florida and would like to identify it. Also, as it has been sitting out in the sun for days, it is dry.  Is there a way to safely preserve this crab, such as incase in a plastic cube.  We would love to save it as a memory of our trip.  Thank you.
Any idea?
Re: What is this crab
Yep, I'm pretty sure I know what that is.  I'll get on it right away.
-Lynn
<Thank you. B>
What is this crab?  Persephona mediterranea – 2/20/13
We found this crab washed up on the beach on Ft Myers Beach Florida and would like to identify it.
<It’s a common species called Persephona mediterranea, aka the “Mottled Purse crab”, in the family Leucosiidae.  For more information, please see the FAQ titled “Crab: Persephona mediterranea - 3/22/11” at the following link: http://www.wetwebmedia.com/twafaqs2.htm?h= >
Also, as it has been sitting out in the sun for days, it is dry.  Is there a way to safely preserve this crab, such as encase in a plastic cube?  We would love to save it as a memory of our trip. 
<I’ve brought home many a small crab carapace, but never a whole crab (that I wasn’t going to eat!), so the best I can  do is recommend an internet search for (hopefully) more reliable results.  In the meantime, I’d do a sniff test.  Basically, if the crab smells to high heaven then you’ll definitely need to do something about the rotting flesh inside.  That is, either find a way to dissolve or desiccate/mummify it.  If there’s very little to no smell at all, I’d leave the crab out awhile longer in a dry, open area, just to be sure all moisture it gone, then encase it if you like.  In the meantime, here’s something from a taxidermy site: http://www.taxidermy.net/forums/BeginnersArticles/00e/0086A63B9C.html
Thank you.
<You’re very welcome and good luck with your project!  Take care, Lynn Z>

Crab ID and Anatomical Question: Probable Xanthid   /LynnZ – 12/12/12
Hi wonderful experts! 
<Hello there, Tim and thanks! I’m not sure that I fit into the expert category but there are certainly those here that do!>
This crab arrived on my live rock about a year ago, not much bigger than a pistachio. 
<It’s a neat-looking little crab.>
Now he's about 2 1/2 inches wide and still growing.  He's in a tank with just one fish, a flame Hawkfish.  I worry that the fish may be in danger. 
<I can certainly understand that.  Crabs are opportunistic omnivores that pose an increasing risk to fish, snails, etc., as their size and appetite grow.>
I've looked closely at his claws. 
<Excellent, you can tell a lot about a crab by studying the shape of its claws and legs.>
They are strong but short and cannot open wider than about 1/4 inch, maybe not even that far.  Also, they are blunt and knobby, not sharp at all.  I suspect that he normally eats small snails. 
<I can’t quite see the claws all that well, but in general, robust versions with large, knobby/blunt “teeth” (referred to as “molariform” = molar-like) are typically used to break through shells, (e.g. Mollusks, other crabs, etc.).  Sometimes these crabs will have one large claw for crushing and another, smaller one, for picking and/or cutting.> 
I feed him krill, and I've got him trained to come out and beg for food that I give using long tweezers.
<Good, those claws can put some serious hurt on you so keep the tweezers/tongs handy!>
Anyhow, I have three questions, if I may:
1) Given that his claws are short and blunt, do you think he'd be apt to kill my Hawkfish?
<It’s possible if the fish was unhealthy/compromised in some way, or maybe at night, if the fish was at rest, and cornered.  Even with blunt claws, a crab can still grasp something, hang onto it and kill it.  Again, the risk factor increases with the crab’s size and appetite so be sure to keep it well-fed.>
2) Can you perhaps ID him from these two pictures?
<Hmmm well, I suspect that it’s a Xanthid of some sort, but that’s as far as I can take it.  Even if I knew exactly where the crab came from originally, and had it right in front of me, it would still be a daunting task to get a concrete ID.  There are just too many genera and species out there and each can vary to a surprising degree.  Suffice it to say that it’s a pretty little crab, but do keep an eye on it because it could get very big and very hungry!>
3) I can't figure out where his eyes are. 
<They’re large, white, with small pupils, located at the front edge of the carapace.  The arrow on the right side is aimed directly at one. >
He has a pair of central 'antennae' that are long, thin, very flexible, and constantly flit about.  Are those tiny eyestalks? 
<If you’re referring to the thick(-ish) appendage where the left arrow points, no, that looks like either one of the crab’s antennules (small antennae) or one of the many mouthparts.  The front end of a crab is a mixture of many moving parts, including the eyes (sometimes on long stalks), one pair each of antennae and antennules, and a host of mouthparts including three pairs of specialized feeding appendages known as maxillipeds, two pairs of maxillae, and one pair of mandibles.  Please see the following link for diagrams and more information regarding crab anatomy:  http://lanwebs.lander.edu/faculty/rsfox/invertebrates/callinectes.html 
He also has a further apart pair of eyelike things on his shell.  I marked one of each of these on the first photo.  Thoughts?
<Heheee, yep, the eye-like things are eyes!  The object at the left arrow is mentioned above.>
Thank you very much!
<You’re very welcome!>
Tim
<Take care, Lynn Z>
Crab ID and anatomical question    /BobF        12/12/12
Hi wonderful experts!  This crab arrived on my live rock about a year ago, not much bigger than a pistachio.  Now he's about 2 1/2 inches wide and still growing.  He's in a tank with just one fish, a flame Hawkfish.  I worry that the fish may be in danger.  I've looked closely at his claws. 
They are strong but short and cannot open wider than about 1/4 inch, maybe not even that far.  Also, they are blunt and knobby, not sharp at all.  I suspect that he normally eats small snails.  I feed him krill, and I've got him trained to come out and beg for food that I give using long tweezers.
Anyhow, I have three questions, if I may:
1) Given that his claws are short and blunt, do you think he'd be apt to kill my Hawkfish?
<Not unless the crab gets, is much larger, no>
2) Can you perhaps ID him from these two pictures?
<Due to overall shape, coloration/marking, am guessing this is a member of the genus Lissocarcinus>
3) I can't figure out where his eyes are.
<The one on the right you have labeled...>
  He has a pair of central 'antennae' that are long, thin, very flexible, and constantly flit about.  Are those tiny eyestalks?
<Not; these are antennae: http://library.thinkquest.org/26153/marine/arthro.htm >
  He also has a further apart pair of eyelike things on his shell.  I marked one of each of these on the first photo.  Thoughts?
<As stated, one of the eyes>
Thank you very much!
Tim
<Welcome! Bob Fenner>

Marine Crab Identification     11/12/12
Hello Wet Web Crew,
I'm trying to identify a Crab that's in my 30gal Saltwater Tank. I attached three pictures of it (below). It's very small, with a white body, orange legs, and orange eyes. I think its nocturnal as it does not come out much during the day. I've spent hours searching forums trying to ID this little guy and have come up blank. Any idea what he is? 
I'm trying to start a reef tank and would like to know if he'll be safe to keep or not. 
Thanks so much,
Roberta
<Roberta; your pix didn't "come over". Please re-send as attachments... and try sending to yourself as well...
Cheers Bob Fenner>

Mystery Crab ID? 6th November 2012
Good Morning Crew!
<Hi Paul>
Last night, I finally managed to catch a hitchhiker who has been bugging me for a while! The culprit is a crab with red eyes (picture attached).
<I see this>
I know it has been responsible for the consumption of a biscuit starfish in the past couple of months and possibly the loss of a small female mandarin.
<Could well be>
I've searched your ID pages a couple of times and I am 99% sure that it matches the crab on page 2, topic 'Crab ID? 12/5/03'. That was a while ago and there didn't seem to be any definitive ID, so I thought I would ask again.
Those red eyes.... So glad to have them out of the display and in the sump!!
<Mmm, well; my first guess was that this might be a member of the genus Calappa; perhaps Calappa hepatica (Linnaeus 1758). I do agree w/ the linked image/response you cite here: http://wetwebmedia.com/swcrabidfaq2.htm
I would isolate this animal/Decapod in any case; it's likely to consume other life in your system>
Many thanks in advance for any help you can provide in the ID!
Kindest regards,
Paul.
<Welcome. Bob Fenner>