The enigmatic cnidarian Martsaphyton moxi gen. et sp. nov. from the Darriwilian (Middle Ordovician) of Estonia

On the basis of detailed SEM-EDS study and computer tomography scanning, the single specimen of the enigmatic Martsaphyton moxi from the Aseri Stage (Darriwilian; Middle Ordovician) of Estonia was identified as a member of the phylum Cnidaria and subphylum Medusozoa, with unspecified (incertae sedis) class placement. Our results confirm a number of similarities in the morphology and chemical composition with previously described Sphenothallus Hall 1847 and Torellella Holm 1893, also interpreted as cnidarians. All three show tubiculous morphology, lamellar skeleton structure and calcium phosphatic composition. The new species differs from the previously described members in its unique root-like appendages, widened apertural chamber and lack of a laterally thickened skeleton wall. The element analysis revealed an unexpected chemical composition - high content of silica, iron, aluminium, potassium and sodium - of the rock matrix surrounding the specimen, which suggests possible involvement of material of volcanic origin in the sediment.