Hundreds of fragments of P. paradoxissimus have been found at many localities in Scandinavia, but nearly all are isolated sclerites. Entire specimens are very rare. The type specimen is one of the complete examples and it is 12 cms long, but large fragments show that some P. paradoxissimus reached at least twice that size.
The isolated sclerites mostly originated from moulted exoskeletons, and sometimes accumulated in shallow water by wave and current action. The more complete exoskeletons are mostly found in off-shore muds that were deposited in deeper water.