Paleonet: Unidentified microfossils?

Joseph Botting acutipuerilis at
Thu Mar 30 04:48:08 GMT 2017

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_______________________________________________
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