Campanian (Late Cretaceous) hexactinellid sponges from the white chalk of Mielnik (Eastern Poland)

The taxonomic description of the Campanian (Upper Cretaceous) hexactinellid sponges from the white chalk of Mielnik, eastern Poland, is presented. The fauna comprises 19 species belonging to 15 genera, representing by the Hexactinosida and Lychniscosida. The species Polyopesia macropora is described as new. They represent a typical sponge assemblage of the North European Province. Most of the specimens are strongly phosphatized (85% of the material), less common are grey-beige, slightly phosphatized specimens (11%), and distinctly rarer are specimens infilled with white chalk (3%) and silicified specimens (1%). Phosphatization was the dominant fossilization process of the hexactinellid sponges in the white chalk of Mielnik.