Bidder, 1898
Definition: Calcarea with the triactines and the basal system of tetractines sagittal (i.e. the rays of the spicule make unequal angles with each other), exceptionally regular. In ontogeny the first spicules to be secreted are diactines. Choanocytes are apinucleate. Calcaronea have amphiblastula larvae.
Source: Borojevic et al., unpublished
Orders: There are two orders: Order Leucosolenida Hartman, 1958b and Lithonida Vacelet, 1967. The latter has no representatives in the area and will not be treated here.