a class of extinct animals conventionally assigned to the phylum Porifera. The Sphinctozoa lived from the Carboniferous to the end of the Cretaceous. They included both solitary and colonial forms measuring about 20 cm in height. The calcareous, porous skeleton is in the form of a cube or cylinder. The internal cavity is divided into separate chambers by horizontal septa. Some species have a tube that isolates the central cavity. Vesicular tissue may be found in the chambers and central cavity. The Sphinctozoa included about 30 genera.