Paleonet: Unidentified microfossils?

Andrzej Pisera apis at
Fri Mar 31 09:21:47 GMT 2017

Dear Tim,

your are wrong. These spicules, as it was expalined already by Joseph, 
are typical Geodia sterasters and they have nothing to do with 
selenasters typical of Placospongia. By the way, selenaster are 
bean-shaped naturally, not due to etching.

Fossil Geodia sterrasters are common since Eocene at least, and 
described from different parts of the world, including the US (long time 
ago by Rigby, paper in Journal of Paleontology, if I remeber well) and 
myslef from the Miocene of Europe (Palaontol Z (2014) 88:263–277, DOI 
10.1007/s12542-013-0197-x, and Rivista Italiana de Paleontologia 2005, 
112, 287–299, for example) or Eocene od Australia by M. Lukowiak 
(Zootaxa 3917 (1): 001–065) and Europe by V. Frisone (Facies (2014) 

all the best

W dniu 2017-03-30 o 10:35, Timothy Palmer [tjp] pisze:
> ...and you might like to look at papers by Rutzler and Macintyre from 
> the late 1970s.  I recall work on the Belize reef, and one of the 
> papers was in Marine Biology.  The genus was Placospongia.  They 
> showed the gradual etching of these microscleres down to bean-shaped 
> selenasters.  I later encountered them in micropal samples picked by a 
> long-forgotten student
> Tim Palmer
> ------------------------------------------------------------------------
> *From:* paleonet-bounces at <paleonet-bounces at> 
> on behalf of Trenton J. Ryan <tr86 at>
> *Sent:* 30 March 2017 06:35
> *To:* Joseph Botting; paleonet at
> *Subject:* Re: Paleonet: Unidentified microfossils?
> Thank you for the suggestions everyone. Gwen got me pointed in the 
> right direction, and Joe confirmed my findings. Thanks Gwen and Joe!! 
> They are "adult" sponge sterrasters from the /Geodia/ genus of sea sponges
> On Wed, Mar 29, 2017 at 9:48 PM Joseph Botting 
> <acutipuerilis at <mailto:acutipuerilis at>> wrote:
>     Hi Trenton,
>     Yes, indeed it is a sponge - these are sterrasters from a geodiid
>     demosponge. Very distinctive microscere spicules!
>     See, e.g.,
>     All the best,
>     Joe
>     ------------------------------------------------------------------------
>     *From:* Trenton J. Ryan <tr86 at <mailto:tr86 at>>
>     *To:* paleonet at <mailto:paleonet at>
>     *Sent:* Thursday, 30 March 2017, 0:36
>     *Subject:* Paleonet: Unidentified microfossils?
>     Hello,
>     I am working on a masters thesis and have found numerous examples
>     of a thus far unidentified microfossil? and have taken some SEM
>     photomicrographs of them, found here:
>     <>
>     The specimens in question were found in Northern California in the
>     late Miocene Saint George Formation  (sandy mudstone). Occurrence
>     of them seems to be limited to the shelly deposits within the
>     formation, as they are not found in the strata between prominent
>     shell beds. The macrofossils in the shell beds are mostly made up
>     of /Macoma inquinata, //Macoma secta, /and less frequent /Solen
>     /sp./, Clinocardium /sp., and /Nassarius /sp.. The only forams
>     that I have found in the shell beds are /Elphidium/ sp., which are
>     rare.
>     Under a regular light microscope and when wet, the unidentified
>     specimens appear translucent with a more opaque, milky-white
>     central 'nucleus'. This 'nucleus' accounts for ~20% of the total
>     volume per specimen and is not apparent (visually) when dry. All
>     of them have an ovate form, and do not vary much in terms of size.
>     They are likely siliceous, as they do not react to HCL.  As you
>     can see in the SEM images, they also exhibit an intricate stellate
>     pattern.
>     Any ideas on what they could be? Some suggestions thus far are
>     octocoral sclerites, dinoflagellate cysts, or fossilized pollen.
>     Thanks,
>     Trenton Ryan
>     tr86 at <mailto:tr86 at>
>     Humboldt State University
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Andrzej Pisera
Instytut Paleobiologii PAN
ul. Twarda 51/55
00-818 Warszawa

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