I have never seen, or heard of, rads with plates and sutures. Is it a rad - is the shell made of opal? Do you have only this one specimen? If you have several, it would help to mount one for transmitted light so the internal structures can be seen.
Dave Lazarus (2003/02/26)
I agree with Dave. It should be made clear whether the test is made of opal
(or, at least, an opal-mix) or not.
In the latter case it might even be a dinoflagellate (although our local dino expert,
Jens Matthiessen, told me that he had never seen such a cyst, and the surface looks
too stable to be organic walled, suggesting an opal/carbonate composition).
If the shell is mostly made of opal, and radiolarian must it be, then the closest
I could come with is a Phaeodaria:
Circorrhegma (Haeckel 1887, Plate 117, Figure 2), with pentagonal plates, and simple spines,
but lacking the two bipolar spines Shyam's specimen has.
Giuseppe Cortese (2003/02/26)
Peppe and Dave do question if this is an opal microfossil. I will say it is. Assuming this should be a skeleton with an organic compound, we would not have observed the typical "opal dissolution pits" as seen on the main spine, especially on the right one, but they are also vaguely observed on the left main spine. A siliceous skeleton is therefore my guess. We have to await the answer from Shyam on this problem.
Siliceous dinoflagellate cysts are well known. I have no experience in this group, but the “pentagonal plate structure” do lead me to conclude that this is no radiolarian at all. Peppe do hint that it could be a phaeodarian, but I doubt that too. The phaeodarians as indicated in Haeckel do certainly have polygonal structures, but they are usually separated by silicified ridges, not by these “sipper-like” structures as in the figured specimen.
I would, as David, challenge Shyam to verify the skeletal material. Then the second challenge would be, as a SEM is available, to crush on specimen to observe the skeletal wall in cross section. A polycystine radiolarian wall is quite solid, a phaeodarian wall is spongy (bubble like), while I do not know the structure of a silicified dioflagellate skeleton.
Never the less, my present guess is: This is a silicified dinoflagellate cyst. Make other dinoflagellate people aware of this page.
Kjell R. Bjørklund (2003/02/26)
It's an acantharian. Dorataspis sp.
Stan Kling (2003/02/26)
Guess Stan is right
I have scanned two pictures from Reschetnayak 1981 (Right: Coleaspis sp.; Left: Dorataspis sp.), and the two genera represented here show the typical structures as depicted in Shyams "Mystery Rad". I guess the problem is solved.
Kjell R. Bjørklund (2003/02/27)
Here is somebody that knows the literature on radiolarians in the old sense. It was clear from the beginning that it was an acantharian because of the disposition of the spines according to the Muellerian law. And, secondly, only
some acantharians have plates. The image is very good and the position is perfect, better than in Reschetnjak.
Paulian Dumitrica (2003/02/28)