The hexactinellid sponge Cyathophycus from the Upper Ordovician of the Argentine Precordillera

Abstract

A nearly complete specimen of a hexactinellid sponge has been recovered from the Lower Ordovician siliciclastic rocks of the Argentine Precordillera. The material was collected in the upper member of the Los Azules Formation (Sandbian). A new species of the genus Cyathophycus Walcott is erected. The taxonomic position of the genus is still controversial; their recent assignment to the family Dictyospongiidae is discussed. Cyathophycus was considered as a transitional form between protospongiids with simple regular skeletons and dictyospongiids with quadruled, more complex skeletons. Previous studies stated that the hexactinellid record through the Cambrian–Ordovician interval, like other sponge groups at this time, appears to have been on strengthening the skeleton, and occupation of more turbulent, shallow-water environments while remaining dominant in deep-water settings. Cyathophycus is a typical representative of this transitional stage in which the skeleton is simple, but double layer with bundled spicule rays; and still not enough rigid as the typical dictyosponge skeletons. Lower and Middle Ordovician records came from black shale deposits, while younger occurrences show slightly different environmental settings (mudstone, shaly mudstone and dolomites), shallower but also quiet water deposits.