Teganium (Porifera, Hexactinellida) from the Middle Ordovician Castle Bank fauna of Avalonia (Wales, UK)

The hexactinellid sponges Teganium and Teganiella are widespread in Ordovi-cian, Devonian and Carboniferous strata in Laurentia, but have not previously been reported outside that palaeocontinent; some other members of the family Teganiidae are also restricted to Laurentia. The genus Teganiella in particular is considered to be a Laurentian endemic, with all species specialised for equatorial, shallow-water condi-tions. However, it is now clear that the diagnostic separation of Teganiella from Tega-nium was based on misunderstanding of the latter, and Teganiella should be considered a junior synonym. Based on this prior distribution, the discovery of two new species of Teganium (T. avalonensis sp. nov. and Teganium sp.) from the Middle Ordo-vician (Didymograptus murchisoni Biozone) of Castle Bank, Wales, is unexpected. These species are the oldest known and indicate diversification of the genus within a temperate microcontinent, prior to its appearance in Laurentia. The exceptional preser-vation of the new sponges also reveals detail of a complex body wall, supporting a more derived phylogenetic position within Hexactinellida (possibly affiliated to the Lys-sacinosida) than previously recognised. The palaeobiogeography may suggest a rela-tively deep-water origin for the group (as for modern hexactinellids), which then became secondarily specialised for shallow-water environments within a Laurentian diversification.