[6] All sponges in this class are strictly marine, and, while they are distributed worldwide, most are found in shallow tropical waters.

All three sponge body plans (asconoid, syconoid, and leuconoid) can be found within the class Calcarea.

[7] Calcareous sponges vary from radially symmetrical vase-shaped body types to colonies made up of a meshwork of thin tubes, or irregular massive forms.

Some older studies applied the name Calcispongiae to the class, though "Calcarea" is much more common in modern nomenclature.

Some molecular analyses suggest the class Calcarea is not exclusively related to other sponges, and should thus be designated as a phylum.

Borchiellini et al. (2001) argued that calcareans were more closely related to Eumetazoa (non-sponge animals) than to other sponges.