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Extinct genus of Cambrian Arthropod From Wikipedia, the free encyclopedia
Mollisonia is an extinct genus of Cambrian arthropod. 4 species had been described from North America and China. Studies suggest it is a basal member of Chelicerata, a group which includes horseshoe crabs and arachnids.[1][2]
| Mollisonia Temporal range: | |
|---|---|
| |
| Reconstruction of Mollisonia plenovenatrix | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Order: | †Mollisoniida |
| Family: | †Mollisoniidae |
| Genus: | †Mollisonia Walcott, 1912 |
| Type species | |
| †Mollisonia symmetrica Walcott, 1912 | |
| Species | |
| |
| Synonyms | |
|
Houghtonites Raymond, 1931 | |
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. Below the cephalon was a pair of huge compound eyes, followed by a series of walking legs and gnathobasic (jaw-like) limbs, each have 3 pairs in total. 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. The gill-bearing trunk appendages may had been solely for breathing. This functional differentiation (head/prosomal appendages for feeding and walking, trunk/opisthosomal appendages for breathing) is closer to euchelicerates (crown-group chelicerates other than sea spiders) than the basal chelicerate genera of Habeliida (e.g. Habelia, Sanctacaris).[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. sinica).[4] Remains possibly attributable to the genus are also known from the Ordovician Fezouata Formation of Morocco and Bøggild Fjord Formation in Greenland.[5]
The taxonomic affinity of this genus was enigmatic until the discovery of its chelicerate features in 2019.[1] Subsequent studies suggest it is a basal chelicerate, closer to crown-group Euchelicerata than members of Habeliida. It is also suggested to be closely related to Corcorania, Urokodia (formerly[6]), and Thelxiope, which together form the order Mollisoniida.[1]
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