All sponges in this class are strictly marine, and, while they are distributed worldwide, most are found in shallow tropical waters. Like all other sponges, they are sedentary filter feeders. All three sponge body plans are represented within class Calcarea : asconoid, syconoid, and leuconoid.
After the Cretaceous, hexactinellid diversity gradually declined towards its present level. Systematics and Phylogeny Hexactinellida is divided into two subclasses, the Amphidiscophora, which have safety-pin like microscleres (amphidiscs), and the Hexasterophora, which have microscleres resembling stars or snowflakes (hexasters).