Highly spherical Radiolaria; does this image accurately depict the organism?
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.