Abstract

CARRERA, Marcelo G  and  ORTEGA, Gladys. The hexactinellid sponge Cyathophycus from the Upper Ordovician of the Argentine Precordillera. Ameghiniana [online]. 2009, vol.46, n.3, pp.449-459. ISSN 1851-8044.

A nearly complete specimen of a hexactinellid sponge has been recovered from 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, C. extendis, is erected. The taxonomic position of the genus is still controversial. Their recent assignment to the family Dictyospongiidae is discussed; Cyathophycus has been considered as a transitional form between protospongiids with simple regular skeletons and dictyospongiids with more complex skeletons. Previous studies have stated that hexactinellid evolution through the Cambrian-Ordovician interval, like other sponge groups at this time, appears to have been based on strengthening the skeleton, and the 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- layered, with bundled spicule rays, and not as rigid as the typical dictyosponge skeletons. Lower and Middle Ordovician records are from black shale deposits, while younger occurrences show slightly different environmental settings (mudstone, shaly mudstone and dolomites), which indicate shallower but still quiet water deposits.

Keywords : Porifera; Hexactinellida; Ordovician; Argentina.