LOL Yep, I know what you mean. Now the trick for me is to remember where I saw the blasted thing! Take care, -Lynn <Know whatcha mean... Hey, where are my pants!? Will do. B> Critter ID: Bivalve Mystery - 6/24/08 Hi there, <Hi Carl, Lynn here this afternoon!> Firstly congratulations on the great site! <On behalf of Bob and the crew, thank you very much!> This is my first marine aquarium and your site has provided me with a great amount of information to help me on my way. <Excellent> I was wondering if you could help me identify this little chap which seems to have hitched a lift on my last batch of live rock. <Will sure try.> He's only a few millimeters in size and brown in colour, the main part of the (shell?) looks like a split seed casing out of which comes a small white worm. <Okay> It moves by basically attaching the (head?) end of the worm <The shape is reminiscent of a clam siphon.> ..to a rock or the glass and then dragging itself along. It seems to be around day and night and doesn't seem to be causing any problems in the tank. <That's always a plus!> Just curious as I've not been able to ID it. http://h7lwpw.blu.livefilestore.com/y1p4IDr1MtfX0zR2RucSIySuNcmVaXc7KuxbCiaLHGLht
FTkVWWLqzE8IFbeJTW3-OK_HeGwiouZZhJjzRoDIj7KA/Untitled-1.jpg?download <Okie doke. Is there any way you can get a higher resolution/more detailed photo of this little guy? If not, that's okay. Hopefully, together we can solve this mystery! When it comes to bivalved critters, the choices that come to mind are mollusks in the Class Pelecypoda/Bivalvia (clams and such), Ostracods ('seed shrimps'/Crustaceans), Brachiopods (aka 'lamp shells'), and Opisthobranch sea slugs in the Family Juliidae. Of these possibilities, the most mobile are the Ostracods and sea slugs. I think we can rule out Ostracods because they have multiple long hair-like antennae protruding from their shells instead of a single, thicker stalk/siphon (whatever that thing is in the photo). See this example of an Ostracod for comparison: http://www.friendsofwarnhamlnr.org.uk/images/pondlife/crustacea/ostracoda/cypris05.jpg Sea slugs in the genus Juliidae are also out because all have two obvious rhinophores/antennae on their heads. I don't see any on your creature and I think you would have noticed them had they been there. By the way, let me know if you take another look at your little guy and do indeed see rhinophores! In the meantime, please see these links for sea slug examples: http://www.seaslugforum.net/display.cfm?id=19650 http://www.seaslugforum.net/factsheet.cfm?base=julizebr . Now we're left with mollusks/bivalves and Brachiopods. Most live either attached to hard surfaces or buried in sediments. Although they're mostly sessile, they can and do move about when very young (before settling) and, if possible as an adult, when necessary. Brachiopods attach themselves to hard surfaces and anchor themselves in the sand by way of what's called a "pedicle" or stalk. Bivalve mollusks (except for scallops and such) use a muscular foot to move about/bury themselves in the substrate, while those that attach themselves to hard surfaces secrete byssal threads as holdfasts. Now that you have some of the general terms, please see the criteria listed below. Hopefully it will help narrow things down. By the way, if you have a magnifying glass somewhere, dig that puppy out and take a close look at your little critter. 1. Pedicle that emerges from a single hole on one side of the shell = Brachiopod. 2. Long, slender pedicle that emerges from what appears to be a hinged area (where the two shell halves meet) = Brachiopod. 3. A Muscular foot that emerges from the open side of two shell halves (not at the hinge) = bivalve/mollusk. 4. Shell with no pedicle hole + foot/siphon that can completely retract into shell = bivalve/Mollusc. 5. Once attached to a surface, the creature is able to pivot about on the stalk/holdfast = Brachiopod. Hopefully this helps! One thing I'd like to mention is that there may easily be other possibilities as well that I'm totally unfamiliar with! As is, I'm inclined to think that what you have is likely a very young bivalve (mollusk) of some sort trying to find a place to settle, rather than a Brachiopod. The reasoning behind this is mainly because the latter is less common. That and the fact that I can't come up with any other possibilities! Please see the following links for photos: Brachiopod (see pedicle): http://www.dse.vic.gov.au/CA25677D007DC87D/LUbyDesc/WPB-lamp_il/$File/lampshell_il.jpg Ostracods as well as a photo of a juvenile bivalve (bottom left): http://www.chucksaddiction.com/hitchpods.html > Many Thanks, Carl. <You're very welcome. Keep in touch --Lynn> Bob- I doubt that that is the animal's foot in the pic of the "bivalve." Could you and Lynn be thinking of "Lamp shells" (Brachiopoda)?  Best, Sara M.
<Dat's a right>

Oh, yeah. B.

Re: Bivalve mystery . 6/25/08 "Bob- I doubt that that is the animal's foot in the pic of the "bivalve." Could you and Lynn be thinking of "Lamp shells" (Brachiopoda)? Best, Sara M.<Dat's a right>" Hi Sara and Bob, Yes, a Brachiopod was most definitely one of the possibilities that came up. I'm hoping that Carl will be able to determine whether he has a mollusk or a Brachiopod by the placement, etc, of that slender appendage. It does indeed look more like a clam siphon or a Brachiopod pedicle to me than it does a mollusk foot, but after seeing Charles' photo of a juvenile clam/scallop at the link provided, I had to admit that the possibility was there (see the photo on the bottom left: http://www.chucksaddiction.com/hitchpods.html ) . That still looks like a foot to me because it's a bit broader at the base, but given the possibility of odd positioning with Carl's creature and a bit of a blurry photo?? I just don't know. I'd actually love for it to be a Brachiopod. Anyway, I'm hoping to hear back from Carl so that we can have this answered! Take care,
-Lynn