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FAQs about Sea Spiders

Related Articles: Pycnogonids (Sea Spiders), Marine Invertebrates, Feeding Reef Invertebrates, Lighting Marine Invertebrates,

Related FAQs: Marine Invert.s, Marine Plankton,

Unidentified Pycnogonid on Halimeda, N. Sulawesi.

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>

Follow-up: Re: Aiptasia? Now, ID's: Sea Spiders and Crabs -- 7/15/09
<Hey there Pete!>
Thanks for the help!
<You're very welcome!>
These are four-legged so I guess they are true crabs.
<Uh-oh. I knew the chances were slim, but I had hopes that these would be of the safer Porcelain crab variety.>
After reading your article it looks like a Grapsid.
Not sure which I like better, the crabs or the gobies!
<Heeee! It's just unfortunate that crabs like to snack on gobies!>
But I think I will take your advice and maybe put these in my refugium.
<Well, just keep in mind that once you put them in there, it's no longer a 'refuge'. It'll be a nice little hunting ground for the crabs, but not such a safe haven for everything else! You could always set up a nano tank for the crabs. That way you'd be able to see more of them. It doesn't have to be anything fancy. Just make sure they have plenty of hiding spaces and that they're well fed so they won't get cranky and kill/eat each other!>
Thanks again,
<It was a pleasure.>
<Take care, LynnZ>

Sea Spiders 5/16/09
I'm new at the salt water tank my girlfriend does most of it. We have about 20 lbs of live rock great circulation and are having problems with what we have identified as sea spiders, they are attacking my anemone and my starfish.
<Doubtful, more likely they were failing anyhow. These two creatures need larger, stable tanks. What do your water tests tell you? Actual circulation, lighting?>
We have taken over 50 of these off the anemone thought we got them all but now there back how do I get rid of these.
<Do a quick google search on WWM and the net and you will find that if these are indeed Sea Spiders, they are
not the problem. Your anemone and possibly the starfish are failing for other reasons.>
Thank you SFC
Jeff Walker
<Welcome, Scott V.>

Zoanthid Spider (Pycnogonid sp.) bite!!! HELP   5/23/07 <Hi tasty human!  Mich here!> I got bit by one of these things on my finger.   <Ouch!> Am I in danger?   <Are you standing in front of a bus?  Holding a lit stick of dynamite?  Perhaps eating something with trans fat?>   Are they poisonous? <No.  They are not poisonous.   More here: http://www.wetwebmedia.com/pycnogonids.htm http://www.wetwebmedia.com/seaspiderfaqs.htm  > I got bit about 4 hours ago and it hurt a bit, but I am not in any pain right now.  It looks a bit swelled up and red but nothing major. <I would keep and eye on it.  If it gets worse consult a doctor.  I think your biggest issue is the possibility of infection.  If you see a red line going up your hand don't waste any time and seek medical attention, can be a sign of septicemia which can be quite serious.  Perhaps a little ice might help reduce the swelling.> [IMG] http://www.zoaid.com/gallery2/main.php?g2_view=core.DownloadItem&g2_itemI d=398&g2_serialNumber=2[/IMG] <Nice picture!> Please let me know any information you guys can. <Hope this helps and you are feeling better soon.  Mich>

Re: Zoanthid Spider (Pycnogonid sp.) bite!!! HELP   5/23/07<Hello again tasty human, Mich here!> Thanks for your help. <You're welcome!  Happy to help!> I am glad to hear I'm ok lol.   <Me too!  But do keep an eye on it.  There are a lot of nasty infections you can be exposed to in marine systems.> Have you ever heard of anyone getting bit by them before? <I personally have not, but I do not have much experience with these creatures either. Mich>   

Re: What Could This Be? A Pycnogonid...Maybe - 04/25/07 Eric and all, <<Hello Jan>> My husband and I looked, and it does not have the "emaciated" look of the sea spider. <<I see...I seem to recall there are some that do appear "robust".  Perhaps some further searching...>> Our rock nester has thick legs, very hairy fur like, thick body, pointy claws at the end, yuck.  Is there any other "look see" or what it might be?  Any thoughts and many thanks for even venturing out there with ideas? <<I still think it could be a Pycnogonid, but if not, maybe it is a species of crab.  There are some small reef dwelling species referred to as "spider" crabs for obvious reasons...including the fuzzy appearance.  A picture would help if you can provide a sharp close-up photo (no more than a few KB in size please).  Eric Russell>>

Zoanthid spiders, Pycnogonids, MgCl2 dipping...  4/18/07 Hi,      I know you have talked about these before, but I couldn't find the answer to my question on the previous forum.      I am a newbie and did not know that I should QT corals (I know better now).  Somehow, somewhere, I have picked up Zoanthid spiders.   <Pycnogonids... some of which do feed on Zoanthids... some are "just" space commensals...>      So far, I have FW dipped the affected zoos, dipped them with coral dip   <... what is this? Oh, the Kent Product... mainly I2 cpd.s> and QT'ed them.  They have been in QT for about a month.  I didn't see anything for the last month, but recently began to notice that some of the zoos looked puny and were drooping.  Tonight about 2 hours after lights out, I turned on the lights and saw a baby spider.  I immediately FW dipped the zoo and got another.  I dipped all the zoos in the QT and got a couple more.  I have had about enough.  This is so disappointing.  I finally just tossed the affected zoos tonight. <?!>      I am writing because I am worried about the zoos that dipped clean on the first go round.  I left these guys in my DT and they seem to be doing fine.   I plan on doing another FW/coral dip tonight on the ones that are not attached to rocks and see what happens.        If I find more spiders, what should I do? <Remove, and dip (in a 1.024 or so spg MgCl2 (Magnesium Chloride) solution (made with clean freshwater...) for half a minute... place all in a new, non-infested system...> I have several colonies that are attached to base rocks in my tank.  If I find spiders in some of the colonies should I take out the base rock and dip/QT it too? <You could... but starving these Pycnogonids out will do the same... just leave them, the existing system w/o food for a month or more...>   I probably weighs about 20#.      I hope you all can help me decide what to do.  I love this hobby but am getting very close to bailing because of the disappointments.  I also received some flatworm infested Chaeto from my trusted LFS.  Now my refugium has a few of them.  What should I do?   <Read... on WWM re...>      Will a sixline wrasse help at all?  Will they eat these things?      Thanks,      Miri    <Read on my friend, read on. Bob Fenner>

Sea Spider? - 06/05/06 I have a quick ID question for you guys.<<and gals>> Let's see if I can give as much information as I can. <<Okay>> I'm not sure it will be enough because I can't get a good pic. <<Mmm...>> I found this thing on my zoas tonight after the lights in the tank went out.  I have 4 zoas colonies and I found two organisms on the same colony.  The rest seem to be clear of them.  These things are about 5mm in diameter, have 8 legs, are a brownish clear color and have radial symmetry.  I would normally say some kind of micro sea star, but I'm not sure.  One was wrapped around the stalk of the zoas, seeming to squeeze it - which makes me think some kind of parasite.  I pulled it off and it was NOT happy - all writhing around.  I found another of the same colony latched onto a rock.  They are not pretty, very insect looking. <<Possibly a sea spider (Anoplodactylus erectus), a carnivorous marine arthropod.  Try a Google search re and see what you think>> I was just wondering what it was, if it's harmful, and what I should do about it. <<If indeed a sea spider it is likely harmful/should be removed>> <Mmm... don't appear that deleterious in the wild... RMF> Thanks so much, Jennifer K. <<Hope that helps.  Regards, EricR>>

Sea Spider? II - 06/06/06 EricR, <<Hello Jenny>> That absolutely looks like what it is! <<Ah!  A successful ID then>> All I can say is yuck! <<Ha!...they are kinda creepy looking...>> I read around and it seems that they may feed on corals and other inverts. <<Is what I know of them as well...though must say, I believe Bob does not consider them as harmful as we might think>> I've had this tank established for almost two years and w/o additions for over 4 months.  Where the heck did it come from?   <<Mmm...likely been there all along, or were spawned from the live rock>> Should I just manually remove them if I see anymore? <<Tis up to you...maybe try observing their behavior...removing if you notice a deleterious effect on your corals>> I only found two that one night, no other time.....  I do not want anything detrimental in my tank!  Help! <<Time for some close observation>> Thanks so much, Jenny <<Happy to assist.  EricR>>

Hi Bob--long time, no see!! Sea Spiders and Euhirudineans Hi Bob, <Bonnie! Long time indeed> Just found your web site with some nice photos of pycnogonids. Check out our website for more info. on these critters! Bonnie <Neat! And a forum as well... will share, post. Bob Fenner> Dr. Bonnie A. Bain Pycnogonid Systematics and Evolution Department of Biological Sciences Northern Arizona University Flagstaff, AZ 86011

Pycnogonids - Sea spiders 5/7/04 Hello again crew, <howdy> Last night I was cleaning out my canister filter.  I usually go nuts about collecting all the little critters that are sucked up so they can be placed back into the system.  Normally they are limited to Amphipods, medusa worms, and the occasional bristle worm.  I came across this little critter, and became immediately intrigued.  He is about 1/8-1/4 inch in length, and can only be described as looking like a stick figure.   <clearly looks like a Pycnogonid sea spider. They are generally difficult to keep alive and tend to be carnivorous. If its living for any length of time in your system, its preying on something: sea spiders eating Aiptasia anemones and hydroids make regular appearances> He is quite active, and I am keeping him in isolation until I can get some sort of a positive ID.  I am attaching a few photos of him in various positions, and with various white balance settings.  I know the pictures may be a bit fuzzy, but it shouldn't turn out too bad.  Thanks in advance for all the help! Steve <fascinating creatures... do some keyword searches with this name and see what you can find. Best regards, Anthony>

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