Bidder, 1898
Definition: Calcarea in which triactines and basal system of tetractines are regular (equiangular and equiradiate) or exceptionally parasagittal or sagittal. In ontogeny, the first spicules to be secreted are triactines. Choanocytes are basinucleate with spherical nuclei. The basal body of the flagellum is not adjacent to the nucleus. Calcinea have coeloblastula larvae.
Remarks: Two orders are recognized: Order Clathrinida (with only free spicules) and Murrayonida (with non-spicular calcareous basal skeletons or plate-like fortification of the surface). The latter is not represented in this file.
Source: Borojevic et al., 1990 (who proposed a scheme for Calcinean evolution)