A new stiodermatid (Hexactinellida, Porifera) from the latest Ordovician of Anhui, South China and its significance for searching the missing link between the Cambrian and late Palaeozoic stiodermatid lineage

Abstract

ABSTRACT The new hexactinellid stiodermatid Turgidaspongia porosa gen. et sp. nov. is described from the Ordovician-Silurian boundary sequence in Beigong of Jingxian County, south Anhui Province, China. The spherical, thin-walled species possessed unique features including unusually large parietal gaps on the body wall, swollen hexactines as hypodermalia, and two different sizes of stauractines as dermalia and parenchymalia respectively. Based on the new material, the family Stiodermatidae is revised here, including five genera after reassessment, i.e., Rigbyella, Thoracospongia, Stioderma, Uralonema, and Turgidaspongia porosa gen. et sp. nov. The new species is well preserved with typical enlarged hypodermal hexactines with swollen rays and large, subcircular parietal gaps, giving an illuminating insight into the affinity between the new species and other taxa in Stiodermatidae. It also provides a link between the Cambrian stiodermatid lineage and late Palaeozoic stiodermatid lineage. The uneven distribution of the swollen dermalia in the new species may relate to the sloughing of the dermal spicules causing by the nutrient deficiency. The unique rigid skeleton structure and unusually large parietal gaps probably represent new attempts on the skeletal evolution of hexactinellids in the Palaeozoic.