Recognizing sponge inSpongiostromaGürich, 1906 from the Mississippian of Belgium

SpongiostromaGürich, 1906 from the Mississippian of Belgium was initially provisionally placed in Foraminifera and subsequently compared with hydrozoans and microbial carbonates. For nearly 100 years, the term spongiostromate has been widely applied to clotted microbial fabrics in stromatolites and oncolites. Examination of the type material shows thatS. mæandrinumGürich, 1906, the type species ofSpongiostroma, consists of numerous juxtaposed millimetric pillow-like masses permeated by thin anastomose sparry microscopic fibers (vermiform fabric) in fine-grained groundmass, locally traversed by millimetric rounded to elongate partly sediment-filled openings. Here we interpretS. mæandrinumto be a lobate sponge composed of mammiform papillae formed by calcified spongin network and traversed by canals and spongocoel. These are typical features of calcified remains of keratosan demosponges. We redescribe and reviseS.mæandrinumand interpret it as a keratosan demosponge with papilliform morphology. This upholds Gürich's (1906) initial opinion thatSpongiostromacould be a sponge and supports suggestions that keratosan vermiform fabric has long been confused with microbial carbonate. SinceS.mæandrinumis not a stromatolite, it is inappropriate to use the term spongiostromate to describe microbial carbonate microfabric.