Final answer:
Calcarea sponges have calcium carbonate spicules and are quite small compared to other sponge classes.
Step-by-step explanation:
The type of sponges that have calcium carbonate spicules and tend to be very small are the Calcarea. Calcarea sponges produce calcium carbonate spicules and do not contain spongin. These sponges are characterized by their small size and pointed spicules made of calcium carbonate. An example of a Calcarea sponge is Clathrina clathrus (common name: red-bearded sponge).
These sponges are distinguished by their calcium carbonate spicules and lack of spongin. Unlike the siliceous spicules found in both Demosponges and Hexactinellida, Calcarea exclusively produces calcium carbonate spicules, which provide structural support for their bodies.