Sponges consist of cells which are only poorly organized into tissues. Water is drawn through many small inlets on the surface of the sponge and ejected through fewer exits. Benthic, mostly in shallow marine environments, but some in deep water and a few in fresh water. The marine stromatoporoids (Cambrian to Cretaceous), commonly thought to be coelenterates, might be included in the Porifera (Hartman and Goreau, 1970). Many so-called tabulate corals (e.g. Chaetetes) may also be sponges.
class DEMOSPONGEA (Cambrian to Present)
Sponges with complex canal systems. Skeleton of spongin and/or siliceous spicules; some groups, including the lithistids, have the spicules fused to form a rigid frame. Shapes very variable. Mostly epifaunal, but some are borers, e.g. Cliona.
class HYALOSPONGEA (Cambrian to Present)
Sponges with a siliceous skeleton; usually with a large exhalent cavity. Formerly called Hexactinellida, but this class does still include the family Hexactinellidae.
class CALCISPONGEA (Cambrian to Present)
Sponges with a skeleton of small calcite spicules. Degree of fusion of the spicules variable. Shape of individuals and complexity of canal systems very variable.
PHYLUM ARCHAEOCYATHA (Cambrian)
Confined to the Lower Cambrian and early Middle Cambrian. Skeleton in the form of a calcareous cup, usually solitary. The walls and some internal plates are porous, like sponges, but other non-porous structures may be present (like corals). Shallow marine, benthic.
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