Paleonet: Unidentified microfossils?

Trenton J. Ryan tr86 at
Thu Mar 30 05:35:06 GMT 2017

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>

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,

*From:* Trenton J. Ryan <tr86 at>
*To:* paleonet at
*Sent:* Thursday, 30 March 2017, 0:36
*Subject:* Paleonet: Unidentified microfossils?


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.

Trenton Ryan
tr86 at
Humboldt State University
Paleonet mailing list
Paleonet at
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <>

More information about the Paleonet mailing list