Protista:
In the Kingdom: Protista lies the multicellular lifeforms. An example of such organisms are the sponge, seaweed and marine algae.

Calcarea:
These are found in marine, deep water enviroments. These organisms are smaller than the other classes and contain spicules made out of calcium carbonate.

Hexactinellida:
They have spicules made up of silica and are six rayed, all members of this class are found in marine, deep water environments. Demospongia:
Also found in marine and deep water environments. They have spicules made up of silica, but these spicules are not six rayed like the Hexactinellida. They may have up to four rays or none at all. Some others within the class are replaced with protein spongin.

Sclerospongia:
It is known to be more alike with the Demospongia, the class has spicules made up of silica, yet they possess a massive basal skeleton made of calcium carbonate.