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If I understand correctly, Cenosphaera spp. is a type of Radiolaria, which is a type of zooplankton. The following is an image of Cenosphaera spp. is from the supplementary material (Figure S2) of the following paper:

F. Lejzerowicz et al., Ancient DNA complements microfossil record in deep-sea subsurface sediments, Biol. Lett. (9) 2013.

Cenosphaera

Question: Does this image accurately depict the organism?

More specifically, in other images of this organism, there are numerous thorns pointing outwards. Is this thorn-less version a natural variation (or e.g. the result of the process of imaging the organism)? Also, is it largely a sphere with a hollow inside?

The authors give the following description of the process involved in obtaining these images.

Eighteen sediment samples were wet washed over 63 μm and 20 μm sieves. The >63 μm residua were dried and picked for radiolaria and foraminifera. From most samples all specimens were picked. Rich samples were divided with a dry microsplitter into fractions, from which at least 100 specimens were picked for each group. Specimens were arranged by taxa on micropaleontological slides. Radiolaria are classified on the generic level, according to the classification utilized by [8]. Foraminifera above the species level are classified according to [9]. In addition, for radiolaria, the 20-63 μm fractions were soaked in peroxide, then washed with tap water and propanol. For each sample, a few drops of suspended material was left on a glass to dry, covered with Durcupan ACM resin and a cover glass. The micropaleontological slides were analyzed under Olympus BX50 light microscope (electronic supplementary material, figures S2 and S3).

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In terms of their hollowness, they all (at least, when they're alive) will have the actual cytoplasmic mass (the organic bits) inside. What we see in the picture, and classify them by, is the mineral exoskeleton. –  Oreotrephes Jul 10 '13 at 23:55
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1 Answer

According to the Marine Species Identification portal, the presence of these thorns is variable. They also vary in size, shape, and the presence of polygonal frames. I don't think there is anything about the imaging process described that would result in the uniform loss of spines (unless the sieve/microsplitter broke them all, but I think that would be a non-uniform loss).

Re: whether it's hollow or not, that appears to be variable too. One species is filled with oil, while another appears to be hollow.

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