Table 1. Comparison of presence and absence of primary characteristics of siliceous sponges (Hexactinellida plus Demospongiae), Calcarea, and Eiffelia.

Characteristic	Silicispongea	Eiffelia	Calcarea
Axial organic filament	1	0?	0
Hexactine spicules	1	1	0
Opal-A in spicules	1	1?	0
Rhomboidal first-order grid	1*	1	1*
Multiple size orders	1*	1	1*
Axial symmetry	1*	1	1*
ACC/Mg-calcite in spicules	0	1?	1
Organic spicule sheath	0	1?	1
Hexaradiate spicules	0	1	1*

1, presence; 0, absence; 1^*, present in ancestral forms but subsequently lost in at least some extant taxa; ?, character state probably as given, based on our observations, but could not be categorically confirmed with the available material.