A Problematical Micro-Organism from the El Paso Group (Lower Ordovician) of West Texas

Mound structures in the Lower Ordovician El Paso Group [Subun B2a of Cloud & Barnes (1948)] contain abundant remains of a problematical micro-organism. Morphologically, this problematical form is a straight to slightly curved, tubular micro-organism that has a conspicuous dark central canal and a distinctive radial-hyaline wall structure. The wall is usually single-layered, but multilayered walled forms are alsoknown. A search of the literature has revealed that the micro-organism has previously bee as Nuia siberica Maslov, 1954, from Lower Ordovician rocks of Siberia. Subsequen Russian writers have reported Nuia from additional Lower Ordovician localities in Siberia and Kazakhstan. They consider Nuia to be an alga, although they do not agree on the major algal group to which Nuia should be assigned. The present writers review the arguments for placing Nuia within one of the present major algal groups and conclude that Nuia should be considered as a problematical micro-organism. The peculiarities of the internal structure of Nuia do not permit its assignment to one of the established groups of fossil algae. A review of all the North American occurrences of Nuia is given, and the genus is emended to include description of multilayered walled forms, a feature previously not considered.