Distinguishing characters of include
- the length of the eye-lobe
- the thick base to the spine on the librigena or ‘free cheek’
- the character of the last thoracic segment and pygidium (tail-plate)
- There are 21 thoracic segments in the known examples
- whereas the very similar Bohemian species P. gracilis (which is known from a large number of complete examples) has only 20 segments.
In trilobites generally
- the mouth and stomach lay under the middle part of the cranidium (head-shield)
- underlying the front part of the head is the hypostome, a large plate which is, in P. paradoxissimus, fused to the rostral plate
- a structure is thought to be associated with a predatory mode of life.