PZ Myers. 2004 Nov 11. Haliestes dasos, a sea spider. <http://pharyngula.org/index/weblog/haliestes_dasos_a_sea_spider/>. Accessed 2008 Dec 01.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Thursday, November 11, 2004

Haliestes dasos, a sea spider

Here's a pretty arachnid—it's phylogenetically rather distant from the more familiar spiders, belonging to its own order, the Pycnogonida, and it's a marine organism, and this particular one has been dead for 425 million years, so I don't think I'm treading on Mrs Tilton's turf. Pycnogonids are primitive chelicerates related to ticks and mites, and they make their living as predators and scavengers. This one, Haliestes dasos, is the oldest sea spider known.

Haliestes dasos and the extant pycnogonid Nymphon gracile. a–j, OUM C.29571, holotype of Haliestes dasos. a, b, d–j, 'Virtual' reconstructions. a, Left anterior oblique stereo pair; b, right lateral view; c, horizontal section number 67 from serial grinding, with inset of proboscis; d, dorsal stereo pair; e, cephalosoma and anterior part of trunk, ventral stereo pair, walking legs largely removed; f, ovigers, antero-ventral view (scale as in i); g, palps, antero-dorsal view (scale as in i); h, chelicerae, dorsal view (scale as in i); i, proboscis, anterior view (ventral up); j, left posterior oblique stereo pair; k, dorsal view, Nymphon gracile, Recent, Galway Bay, Ireland (Oxford University Museum of Natural History, Zoological Collections 2003-13-0015). All scale bars 500 µm. ce, cephalosoma; ch, chelicera; e1–e3, elements of trunk end; et, eye tubercle; lp, lateral process; mo, mouth; ov, oviger; pa, palp; pb, proboscis; s1–s9, segments of appendages; se, setae; te, trunk end; tr, trunk; w1–w4, first to fourth walking legs. Note: w4 distally, on both sides, is not preserved, and the incompleteness, distally, of w2 and w3, right side, and w2, left side, represents data lost in processing. The point of colour change shown here between different structures, such as cephalosoma and chelicerae, is somewhat arbitrary.

920K Quicktime movie

This little guy was discovered in Silurian deposits in England, and one interesting feature is that it was preserved in three-dimensions. That means the fossil itself isn't particularly pretty, unfortunately—it's a stack of thin slices through a block of stone, as can be seen in the frame from a movie at right, illustrating a scan through the whole series. Click on the movie if you want to see the actual fossil itself: it's a shifting pattern of dots and blobs.

In these days of wondrous technology, though, the individual sections can be scanned and stacked and manipulated by computer to produced 3-D images of the animal, as shown in the picture above. The pictures on the left side are all stereo pairs, and if your eyes have the knack of being able to fuse pairs, you'll bee able to see Haliestes dasos pop up out of the screen at you. (Hint: click on the image to get a slightly larger picture. Stick your face up close to the screen and defocus your eyes while looking between two members of a pair, and move your head back slowly. It helped me to cover the other images with a piece of paper to reduce visual distractions.)

Siveter DJ, Sutton MD, Briggs DE, Siveter DJ (2004) A Silurian sea spider. Nature 431:978-980.

1. That's a very strange critter. I couldn't get the movie to work though.
   #: Posted by DarkSyde  on  11/11  at  04:29 PM
2. What and incredibly thin, small creature, that's that first thought that comes to mind. Thanks for the cool stereographic pic, too. Makes it even more interesting. The researchers have got themselves a good hook.
   #: Posted by mattH  on  11/11  at  04:53 PM
3. Oh, it's hardly 'my' turf. I think the world would be a much better place if everybody blogged about spiders. And anyway, I've been lazy about the spiderblogging lately. However, I'm pretty certain that I've determined the large salticid that I inadvertently froze to death as Phidippus sp.</em>, so shall soon post a photo of her, with her gorgeous copper-and-green metallic chelicerae.
   
   Though I have never seen one, I am fascinated by the pycnogonids. Creatures from Mars, if ever an Earth-creature were. Some systematists are uncomfortable classifying them as arachnids, seeing them as a sister-group instead. I think the majority, though, are content to call them arachnids.
   
   It's things like this that make me regret having let my subscription to <i>Nature lapse. It seems like they started publishing all sorts of things I'd have liked to read directly I stopped getting it. But it is terrifyingly expensive, and for an amateur like me the signal-to-noise ratio was too low. I'll stick with Cladistics and the journals of the AAS and BAS. And, if Nature comes out with something really cool, I can always get a précis here.
   #: Posted by Mrs Tilton  on  11/12  at  05:10 AM
4. Oops; sorry about the screwed-up tag...
   #: Posted by Mrs Tilton  on  11/12  at  05:11 AM