Class - Calcarea
The calcareous sponges are characterized by spicules made out of calcium carbonate. All sponges in this class are strictly marine dwellers. The Calcarea are very small, measuring about 3-4 inches in height. Calcareans make up only 3% of all sponges. Species of Calcarea can have radial symmetry or some are asymmetrical. Calcareous sponges are generally sedentary filter feeders, lacking any real tissues. Calcareous sponges are most commonly found in shallow tropical waters. The different shapes of calcareous sponges are relatively simple, either purse, vase, pear or cylinder-shaped.