The siliceous sponges form a major clade of the phylum Porifera, consisting of classes Demospongiae (common sponges) and Hexactinellida (glass sponges). They are characterized by spicules made out of silicon dioxide, unlike calcareous sponges.
Individual siliachoates (silica skeleton scaffolding) can be arranged tightly within the sponginocyte or crosshatched and fused together. Siliceous spicules come in two sizes called megascleres and microscleres.