Synsphaeridium (along with Coniunctiophycus, Symplassosphaeridium and possibly Satka) is a relatively large, pluricellular aggregation fossil that I recently discovered in drill core of the Chamberlain Formation of the Belt Supergroup. It is relatively more abundant than these other taxa, and is described as an irregular, non-linear aggregate composed of contiguous spheroidal vesicles lacking compartmentalized walls within the fossil interior.

As is the case with Symplassosphaeridium, the utility and taxonomic status of Synsphaeridium are also subject to some debate. Both genera describe clusters of spheroidal cells, but Synsphaeridium is frequently recognized as being composed of larger cells that are less tightly packed than Symplassosphaeridium. An interesting feature of the Chamberlain Synsphaeridium, though, is that some specimens appear to have an additional characteristic of smaller, nested spheroidal vesicles (visible to the upper right side of the top two specimens shown here) within the wavy outline of the larger spheroidal vesicles that characterize this form genus. The paleobiological significance of these features, if any, is unclear, but certainly something that differentiates these specimens from others of comparable age.

You can read more about these specimens in my recent GSA Special Paper (Adam, 2016).

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