Cyclestherioides wyomingensis

Close-up of clam shrimp cluster on the center right of specimen.

Clam shrimp (also known as conchostracans) are bivalved arthropods that look like tiny clams, with a carapace (shell) between 2-40 mm in size. They live in fresh water today, but some fossils are found in marine deposits. Inside the clam-like carapace is a tiny shrimp-like creature that filters particles and plankton from the water. Carapaces of clam shrimp from the Green River Formation were the first to be described from the Paleogene of North America (Yan-Bin et al., 2006). This sample comes from a locality in the Lake Gosiute basin and contains several carapaces that can be attributed, on the basis of their size, shape, and growth bands, to the species Cyclestherioides wyomingensis (Yan-Bin et al., 2006).

Close-up of clam shrimp cluster on the top right.

Detail from the back of the specimen (not shown above).

Reference:

Yan-Bin, S., Gallego, O.F., Buchheim, H.P. and Biaggi, R.E., 2006. Eocene conchostracans from the Laney member of the Green River Formation, Wyoming, USA. Journal of Paleontology, 80(3), pp. 447-454. doi:10.1666/0022-3360(2006)80[447:ECFTLM]2.0.CO;2.