HEXACTINELLIDA Schmidt, 1870

Botting, Joseph P., Muir, Lucy A. & Ma, Junye, 2023, Teganium (Porifera, Hexactinellida) from the Middle Ordovician Castle Bank fauna of Avalonia (Wales, UK), Palaeontologia Electronica (a 21) 26 (2), pp. 1-17 : 3

Class HEXACTINELLIDA Schmidt, 1870

Remarks. Although any sponges with hexactins are traditionally assigned to the Hexactinellida, palaeontological evidence implies that these spicules pre-date the class (Botting and Muir, 2018). The majority of early hexactin-bearing taxa have simple, often single-layered skeletons in at least a semi-regular array, and are referred to generally as reticulosans; however, this is probably a paraphyletic grouping of early siliceans, at least. As a result, assignment of fossils to the hexactinellid crown or total group can only be confident when based on specific structures of the skeleton, or the existence of known microscleres (almost never preserved in situ). Crown-group lyssacine (lacking a fused skeleton) hexactinellids differ from most reticulosans in the complexity of that skeleton, with multiple distinct skeletal layers composed of different spicules in different arrangements. The complex wall structure of Teganiella (as seen with additional detail in the new material) supports at least a total-group hexactinellid assignment, and plausibly a crown-group affinity. Specific characters implying a relationship to particular hexactinellid groups are discussed below.