Phylum Porifera Grant, 1836 - sponges Class Hexactinellida Schmidt, 1870 - hexactinellids Subclass Hexasterophora Schulze, 1886 Order Hexactinosa Schrammen, 1903 see Order Hexactinosida Schrammen, 1903 Family Tretodictyidae Schulze, 1886 Subfamily †Placotrematinae Reid, 2004 Genus †Placotrema Hinde, 1883