[1][2] The genus is characterized by a capsule-like dorsal exoskeleton (tergites), which was divided into a subequal size of cephalon and pygidium with 7 thoracic segments in between.

As a Cambrian arthropod, the genus is significant by bearing several traits of now-surviving chelicerates, such as pincer-like mouthparts (chelicerae) and fused ring-like cephalic nerves (synganglion) within their head, as well as a series of multilayered book gills underneath their trunk appendages.

[1][2] Mollisonia may had been a benthic predator, using its anterior chelicerae and posterior gnathobasic limbs to devour prey items while using the 6 legs to walk around the sea floor.

[1] Three species (P. symmetrica, P. gracilis, P. plenovenatrix) are known from the Burgess Shale, with 21 specimens are known from the Greater Phyllopod bed, where they comprise less than 0.1% of the community as of 2006.

[3] The genus is also known from Langston Formation, and Wheeler Shale of North America, as well as Chengjiang Biota of China (P.