A highly diverse siliceous sponge fauna (Porifera: Hexactinellida, Demospongiae) from the Eocene of north-eastern Italy: systematics and palaeoecology

A siliceous sponge fauna, consisting of more than 900 specimens, is described from an early Lutetian tuffite horizon in the Chiampo Valley, Lessini Mountains, north-eastern Italy. Thirty-two taxa (15 Hexactinellida, 17 Demospongiae) are determined and illustrated, belonging to 24 genera, two of which are new (Rigonia gen. nov. and Coronispongia gen. nov.). Among these, 10 new species are proposed: Stauractinella eocenica sp. nov., Rigonia plicata gen. et sp. nov., Hexactinella clampensis sp. nov., Camerospongia visentinae sp. nov., C. tuberculata sp. nov., Toulminia italica sp. nov., Coronispongia confossa gen. et sp. nov., Cavispongia scarpai sp. nov., Corallistes multiosculata sp. nov. and Bolidium bertii sp. nov. Of the genera identified at Chiampo, 14 range back to the Cretaceous, three to the Jurassic and one to the Triassic, while six are still extant. The studied fauna shows affinities with sponges from the Eocene of Spain and the Cretaceous of Germany. The sponge fossils are uncompressed and bodily preserved, but the original siliceous skeleton is dissolved and substituted by calcite. Delicate attachments can be nevertheless documented: some sponges attached to a hard substrate by encrustation, while others were anchored on soft sediments by root-like structures. The presence of different modes of attachment suggests heterogeneous substrate conditions. Small, possibly young, sponges are recorded too. The sponge fauna is essentially autochthonous and lived in the middle-outer part of a carbonate ramp, where it formed clusters. This study extends the geographical and stratigraphical range of many sponge taxa, including Camerospongia, Toulminia, Ozotrachelus and Bolidium, previously documented only from the Cretaceous. The Recent calcified demosponge genus Astrosclera is reported here in the Cenozoic for the first time, having been reported previously in the Triassic only. Additionally, this study documents the second worldwide occurrence of the Recent sphinctozoan genus Vaceletia in the Palaeogene, formerly recorded exclusively in Australia.

http://zoobank.org/urn:lsid:zoobank.org:pub:B3466955-8E20-429A-89BE-42BAEB4002E8